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We have found the following classroom demos to be very useful. None of these demos should be attempted without appropriate safety precautions which includes, in all cases, safety glasses for both the demonstrator and the audience. Some of the materials listed should only be used by appropriately trained personnel. These materials include all vacuum pumps, acids, bases, and dry ice.
Acid-Base Indicators
Indicators are substances used in chemistry to determine whether a solution is acidic or basic. They have different colors in acidic or basic solution. Litmus is one of the most common indicators. It is red in acid and blue in base. Indicators can be made from a whole host of plant materials.
The indicators are prepared by boiling the plant material in water for about 30 minutes, cooled, and then filtered (or decanted) to give the indicator solution. The best flowers are deep purple or red such as carnations, sweet peas, roses, snapdragons, tulips, etc. Other excellent indicators can be made from red cabbage, beets, tomatoes, blackberries, plums, and even blackberry jam. Red is the common color in acidic solution while green, yellow, or purple are common for basic solutions. Tomato skins give an indicator which is colorless in acid solution but yellow in basic solution.
The students can test their indicator solutions on a water solution of baking soda (sodium bicarbonate) which is basic or pure vinegar (5% acetic acid) which is acidic. Once they know the color change of their indicator then they can test water solutions of a whole host of household items such as soap, alum, detergent, lemon juice, baking powder, ammonia, washing soda, etc.
An interesting variant on this experiment is to change the color of flowers by introducing a cotton ball soaked in ammonia solution to a small jar containing a red colored flower. This will change the water in the flower petals from an acidic environment to a basic one and thus after a few minutes bring about the same color change observed above with the indicator solutions. Perhaps your students may even be aware of the Hydrangea shrub that changes the color of its blossoms depending upon whether the soil is acidic or basic.
Cloud Chamber
Add a cup of warm water to a large flask or bottle. Turn the bottle on its side and insert a burning match in the bottle using a tweezers (or you can use a long fireplace match). Allow the match to burn for about 20 seconds and then extinguish the match and allow the smoke to stay in the bottle. Attach a bicycle pump to the flask by pushing a sports ball needle through a tight fitting rubber stopper. Pump about 5 or 6 times and then release the pressure. The expanding gas will cool and thus condense water vapor to cause clouds to appear. The water will condense on the smoke particles making a dense fog. If you then pump up the pressure again the clouds will disappear. Compressing gas causes it to heat which will vaporize the water droplets and the clouds disappear. This cycle can be repeated many times.
This experiment illustrates the fact that a low pressure front will mean cloudy skies and possibly rain, while a high pressure front will mean clear skies. There needs to be dust particles in the air in order to have cloud formation. The smoke particles serve this purpose in the demonstration.
Heat Conduction -
a) Water can be boiled in a paper cup filled with water and the cup will not be burned or charred. The cup must have a flat bottom without a lip or the lip will burn. The cup should be filled nearly to the top so that the top of the cut does not burn.
b) Place ice water in one glass and room temperature water in a second glass. Shortly water droplets will appear on the ice water glass. Place ice water in an insulated glass or vacuum bottle and no water droplets will appear.
c) Have a student grasp a 6" steel pipe in one hane and a 6" plastic pipe in the other hand. The metal pipe feels very cool while the plastic pipe feels normal. The metal is a much better heat conduxctor than the plastic and thus heat readily flows from the students hand to the metal pipe causing the student's hand to feel cold.
Disappearing Sign - Paint a message on a sheet of absorbant paper using dilute solution of phenolphthalene indicator (50 mg in 100 mL of water). Spray the message with dilute ammonia solution (available in the household cleaner section of any food store). The message will appear in bright pink letters. Phenolphthalene is an acid/base indicator which turns pink with basic solutions. When ammonia dissolves in water forms ammonium hydroxide which is a strong base. The message rapidly fades as the ammonia evaporates. The ammonium hydroxide is in equilibrium with ammonia and water. As the ammonia evaporates the equilibrium generates more ammonia until all of the ammonia has evaporated and the solution no longer contains any ammonium hydroxide. . The pH will again be below 8 and the message will disappear. The sign can be repeatedly sprayed to bring back the message.
Effect of Temperature on Mixing - Place one drop of food coloring in each of three 1 L beakers containing cold water, room temperature water, and hot water. Note that the mixing is more rapid the hotter the liquid. Warmer molecules move faster.
Air Pressure Experiments
a) Place a thin wooden ruler (or other similar wooden material) on a table with about one half of the ruler sticking over the edge. Lay a sheet of newspaper over the ruler so that the part on the table is completely covered. Carefully press all of the air from under the newspaper by spreading your hands from the center of the newspaper to the edges. Then strike the ruler very sharply with a stick on the part extending over the table. The ruler will easily be snapped off.
b) Wet the rims of two plumbers plungers and then press them tightly together. It is quite difficult to pull them apart as long as you pull in a straight line. This is a simple example of the famous Magdeburg experiment carried out in 1654. Otto von Guericke showed that it took 16 horses (two teams of eight) to pull apart two iron hemispheres which had been placed together and evacuated. Small replica spheres are available from Carolina Biological Supply Co. They work very well.
c) Partially blow up a balloon; then place a coffee cup on each side of the balloon; and then blow the balloon up some more. You can now lift the two cups with the balloon.
d) Place about a half cup of water in a one gallon can with a screw cap. Place the can on a flame and boil the water with the cap removed. When the water has boiled vigorously for a few minutes remove the can from the heat source and quickly screw on the cap. The can is slowly crushed. Heating the can gently will return the can to its original shape. The reheating should be done in front of a safety shield. The same effect can be demonstrated by pouring some hot water into a plastic Coke bottle and sealing the top. The plastic bottle will be slowly crushed. As an alternative experiment boil a few mLs of water in an aluminum soda pop can and then rapidly invert the can into a dish of ice water. The can collapses with a loud popping sound. The inverting is easily done using a pair of tongs (kitchen tongs work very well) or gloves (garden or work gloves work well).
e) Stuff a cloth into a small bottle, invert the bottle and place the inverted bottle under water. Remove the bottle and demonstrate that the cloth has remained dry.
f) Attach a balloon to the end of a piece of glass tubing which protrudes through a rubber stopper. Place the stopper into a vacuum filtration flask so that the balloon is inside the flask and the other end of the glass tubing is open to the air. Pull a vacuum on the flask. The balloon inflates.
g) Build a Cartesian Diver demonstration by floating a one-half dram inverted vial (about 1/3 to 1/2 full of water) in a two liter plastic pop bottle filled about two thirds with water. A small perfume bottle will also work well. Add enough water to the vial so that it just floats on the surface of the water in the large bottle. Screw the cap on the plastic bottle and squeeze the plastic bottle to make the diver sink to different levels. Upon releasing the plastic bottle, the diver returns to the surface.
h) Fit a round-bottom flask with a tightly fitting cork or rubber stopper through which passes a piece of glass tubing about 12 inches long. The demonstration works better if the glass tubing is drawn into a small opening at the end in the flask. Place 10-15 mL of water in the flask so that the water does not cover the tip of the glass tubing. Heat the flask over a flame so that the water boils for a minute or two. Quickly invert the flask and put the protruding glass tubing into a beaker of colored water. The colored water will rise up the glass tubing and form a fountain inside the inverted flask.
i) Tightly close a small bottle with a cork or rubber stopper. Place the bottle inside a bell jar or vacuum flask. Attach the vacuum pump and remove the air from the flask. The cork pops out of the flask.
j) Place two small bottles in a bell jar or vacuum flask. Fill one bottle about half full with water and attach a rubber stopper with a piece of glass tubing reaching almost to the bottom. Run a piece of rubber tubing from the end of the glass tubing into the second bottle. Remove the air from the vacuum flask. The water is rapidly transferred from one bottle to the other.
k) Place a weighted upright candle (with a reasonably long wick) in a shallow Petri dish (or bowl) filled about half full of water dyed with food coloring. Light the candle and slowly place the open end of a cylinder (sealed at the other end) over the candle, finally standing the cylinder upright in the Petri dish with the candle in the center of the cylinder. The colored water will rise up in the cylinder. (The correct explanation for this phenomenon is not as simple as you might think.)
l) Boil 10 mL of water in a round-bottom flask, remove the heat source and immediately place balloon over the end of the flask. The balloon is slowly pushed into the flask by the outside air pressure until it is pressed completely against the inner wall of the flask. Heating the flask will push balloon out of the flask and blow it up. (Be careful not to melt the balloon while reheating the flask).
m) Fill a small crystallizing dish with fresh marshmallows and place in a bell jar. When the jar is evacuated the marshmallows swell to many times their original volume. If the air is suddenly let back into the jar, the enlarged marshmallows shrink to about one quarter of their original size. With younger children you can make a marshmallow person with toothpicks. Mentioning the Sta-Puft marshmellow man from Ghost Busters I works well. You can also make a Marshmallow person with toothpicks and watch the person enlarge and shrink as you plly and release thre vacuum.
n) Fill a water glass to the top with water. Place a plate with four pieces of paper toweling on top of the glass and then turn the assemblage over. After about one minute you can lift the glass and the plate will remain attached to the toweling and glass because a partial vacuum has been established in the glass when the toweling absorbed water.
o) A small water balloon on top of a flask can't be pushed into the flask. Boil some water in the flask and then set the water balloon on top of the flask and the balloon rapidly drops through. Turn the flask upside down and heat the flask which will force the water balloon out of the flask.
p) Heat water in a beaker to about 80 °C, well below the bp of water. Using a large (50 mL) glass or plastic syringe with a short piece of rubber tubing attached, draw about 40-50 mL of hot water in the syringe. Holding the syringe upright, push in the plunger to dispel any air in the syringe. Clamp the rubber tubing tightly with a screw type clamp. Holding the syringe with the plunger up, slowly pull on the plunger. As the plunger is pulled the water in the plunger will boil. When the plunger is pushed back in the water will stop boiling . This can be repeated many times.
q) Cool a vacuum erlenmeyer flask in a large open mouth Dewar flask of liquid nitrogen. Then pour some liquid nitrogen into the erlenmeyer flask and place a balloon over the mouth of the flask. Plug the side arm with a small cork and remove the erlenmeyer flask from the liquid nitrogen. The balloon expands to enormous size and breaks. Alternatively, a chunk of dry ice can be used instead of liquid nitrogen.
r) Lightly grease the inside of the neck of 1-liter erlenmeyer flask with Vaseline or stopcock grease. Clamp the flask in a ring stand and gently heat the bottom of the flask for about one minute. While the flask is warm, seat a peeled, hard-boiled egg, narrow end down, in the mouth of the flask. Unclamp the flask and immerse it in ice water and the egg will pop into the flask. Grasp the flask by the neck and invert it so that the egg lodges in the neck. Gently heat the side of the flask with the burner and rotate the flask to avoid scorching the egg. The egg will be forced out of the flask.
s) Instead of heating the flask as in (18) and then cooling it in ice water, the erlenmeyer flask can be placed in the crystallizing dish and then the egg placed in the neck and liquid nitrogen added to the crystallizing dish. The egg will pop into the flask.
t) Blow up three balloons, not fully, to the same size and tie them securely. Leave one balloon for reference and place one balloon on the surface of a bowl full of ice water and a second balloon on the surface of a bowl of hot water. This is an illustration of Charles Law which states that the volume of a gas is proportional to its absolute temperature.
u) Heat about 125 mL of water in a 250 mL round bottom flask until the water boils. Remove the flask from the heat and when the water stops boiling insert a stopper in the flask. Invert the flask and place a closed baggie full of crushed ice on top of the flask. The water in the flask boils.
v) Place a small beaker or flask of water containing a boiling chip in a bell jar. Remove the air from the jar and the water will rapidly boil at room temperature.
w) Put a balloon inside a glass flask or jar and try to blow up the balloon. You can't blow it up unless you place a straw in the flask for the air to escape as the balloon increases in volume.
x) Place a small suction cup against the inside of a bell jar. The suction cup will fall as the bell
y) Place a Baggie tightly sealed over a glass. It can't be pushed into the glass. Put a baggie tightly sealed in the glass and it can't be pulled out of the glass.
z) Fill a glass with water and place upside down in a water filled aquarium. Raise the glass (upside down) part way out of the aquarium and the liquid level in the glass rises above the level of water in the aquarium.
aa) Place finger over straw in glass of water and raise straw out of glass. Water rises above the level of the glass.
bb) Blow up large plastic bag with heavy weight on top of the bag. The air in the bag will lift the heavy weight.
cc) Place opening of a balloon over lip on flask with the balloon inside the flask. The flask should also have a small hole opposite the lip (such a flask, complete with instructions, is available from Carolina Biological Co.). Blow up the balloon so it almost fills the flask and put a cork in the small hole. The balloon will stay blown up when you release your breath. Fill balloon with water and then pull out cork. A fountain will result.
dd) Raise a Person with Air - Take a 40 gallon plastic garbage bag (the thicker the better) and push eight Glad flexible plastic straws through the fold on each side of the bag so that they are evenly spaced with four straws on each side. You must push the straws through the bag from the inside out. Then push all of the air out of the bag and seal where the straws protrude through the bag as well as sealing the open end of the bag with duct tap. Place a piece of 3/4 " plywood (about 2' x 3' with rounded corners and edges so it won't put holes in the bag) on top of the bag. Then have a person sit on top of the plywood. Have eight volunteers push a Scoopy's flexible plastic straw into the end of the Glad straw and blow up the bag with their breath. They will need to put their tongue in the end of the straw while they take a breath or the air will come out of the bag. The second straw can be thrown away and you won't have to worry about germs when multiple classes perform this demo. They should be easily able to raise the chair about 8" off the ground. Alternatively, place the same plywood/person assembly (as in #1) on top of eight large plastic food bags with about 1/4 of each bag sticking out and with the open end out. Place the bags evenly underneath the plywood. Have each of the eight volunteers put a straw into the end of one bag and roll the end of the bag around the straw to seal it tightly. Then have each volunteer blow up their bag (as in #1). Again the plywood will be easily lifted of the ground. This demo will also work with a cafeteria table turned upside down on the floor and about 16 kids (8 on each side) with food bags and straws. You can have several kids stand on the upside down table for added weight.
Carbon Dioxide Experiments (Note that dry ice can quickly result in serious frostbite when placed in contact with the skin)
a) Gases can be tested for CO2 content by filling a balloon with gas and then using a straw to bubble the gas through an acid base indicator solution such as BTB (bromothymol blue) which will turn from blue to green to yellow as carbonic acid is generated. Samples to be tested can be air, breath, car exhaust, and pure CO2 from dry ice sublimation or from vinegar (5% acetic acid) plus baking soda (NaHCO3).
b) CO2 Fire extinguishers. CO2 generated from vinegar and baking soda in a wine bottle can be poured over a lighted candle inside a glass to extinguish the flame. A glass can be used also with a piece of cardboard over the top while pouring to minimize mixing with oxygen. Several candles of different heights in a large bowl containing baking soda are extinguished in order of their height as vinegar is slowly poured into the bowl. Several candles in a trough are extinguished as CO2 is poured down the trough.
c) Large CO2 demo is prepared from a 4 foot high plastic cylinder open at the top and 6-8 inches in diameter. Pour one quart of vinegar into the tube followed by 1 lb of baking soda. Place a flat plastic plate over the top containing a small flange at the top to which a balloon is attached. A very large balloon can be blown up in this fashion.
d) CO2 rocket launch is achieved with vinegar and baking soda added to a plastic bottle and quickly sealing the bottle with a cork. Shortly the cork is propelled across the room by the CO2 pressure.
e) Place dry ice in a sealed balloon and watch the balloon expand.
f) Detection of CO2 by bubbling gases through saturated Ca(OH)2 [lime water]. The calcium carbonate that forms is water insoluble and the water turns cloudy. Limestone is calcium carbonate. The CO2 can be from your breath, dry ice, alka Seltzer, vinegar and baking soda, car exhaust, etc. If you bubble a large quantity of CO2 through the limewater the precipitate that initially forms will redissolve forming bicarbonate ion. Finally, heating the solution over a low flame will cause the CaCO3 to reform and precipitate due to decomposition of the bicarbonate.
g) Bubbling CO2 through various acid base indicators solutions changes the color as carbonic acid is generated.
h) Pour 3 M HCl over various crushed minerals in Petri dishes on an over head projector tests the minerals for carbonate. If effervescence occurs then the mineral contains carbonate. You can test calcite, marble, limestone, quartz, chalk, coral, oyster or clam shells. An interesting variation on this experiment is to place a raw egg in 1 pint of clear vinegar. After 24 hrs the calcium carbonate shell of the egg will have been dissolved leaving the membrane through which the yoke can be seen.
i) Effect of temperature on chemical reactions. Place an Alka Seltzer tablet in each of three beakers containing cold water, room temperature water and hot water. See how fast the bubbles form. You can quantify it by placing the Alka Seltzer solution in a closed bottle with rubber tubing leading to a gas collection device (inverted graduated cylinder in beaker of water) to measure how many seconds it takes to collect 50 mL of gas. Alka Seltzer tablets contain sodium carbonate and a solid acid - Calcium dihydrogen phosphate. The reaction will not occur until water is added. The experiment can also be done by adding 3M HCl to 10 g of solid baking soda in a 250 mL erlenmeyer flask. Quickly placing a balloon over the flask will allow it to inflate with CO2. By using cold acid, R.T. acid and warm water you can measure the rate of inflation of the balloons.
k) A voice activated chemical reaction. A solution of bromo thymol blue (BTB) in 95% ethyl alcohol will turn green when just the right number of students have said "Turn Green" into the flask. After each command the students replace the cork and pass it on to the next student.
l) The effect of pressure on equilibrium is shown by taking a solution of saturated sodium bicarbonate to which a few drops of phenolphthalein solution and a few drops of dilute acid have been added. Attach the flask to a water aspirator. Gas begins to evolve and suddenly the solution turns pink:
m) Dancing spaghetti - fill a quart jar almost to the top with water and dissolve two tablespoons of baking soda in the water. Add a handfull of broken spaghetti and then slowly add up to 100 mL of vinegar. The spaghetti will rise to the surface and go to the bottom and then rise again, etc.
n) Foam production - Pour a solution of 1 Tbs of laundry detergent in 50 mL of white vinegar into a solution of 1Tbs of baking soda in 50 mL of water. A large amount of foam is generated.
o) Disappearing ink - Make a solution of thymolphthalein in 50 mL of ethyl alcohol or rubbing alcohol. Add a few drops of 1 M NaOH to make the solution blue. Place this in a spray bottle and spray it on a cloth or write a message with it on filter paper. In a few seconds the blue color begins to fade and eventually disappears. The indicator changes blue from about pH 9.3 - 10.5. Reaction of the NaOH with CO2 in the air produces sodium carbonate which is not basic enough to make the indicator blue.
p) Oxidation of Carbon by Copper Oxide. Place 1/4 teaspoon of Copper (II) oxide in a test tube along with 1/2 tsp of powdered charcoal. Attach a delivery tube to the top of the test tube. Heat the contents gently and use BTB, limewater, etc. to show that the evolved gas is carbon dioxide. Copper metal plates out on the sides of the test tube.
q) Measure the amount of CO2 in a bottle of soda by placing a cork with tubing leading to a water displacement collection vessel. Place the soda can in a container of hot but not boiling water. See how much CO2 can be collected. Do tests to show that it is CO2.
r) Place 50 mL of club soda in a beaker and add a few drops of methyl red indicator solution ( red when pH >6). Fill a syringe half full of the solution, remove the air, seal the syringe and then pul out the plunger to lower the pressure. The solution turns red and then goes colorless again when the pressure is returned to atmospheric pressure. The equilibrium is shifted to the left by lowering the pressure thus removing the carbonic acid and raising the pH of the solution. When the pressure is higher the equilibrium is shifted to the right forming carbonic acid and lowering the pH.
s) Demonstration of the fact that the buoying effect of air on an object depends on the volume of the object. The experiment requires a top loading balancing weighing to ± .01 g. Place a stoppered erlenmeyer containing 2M NaOH inside a plastic bag and then fill the bag with CO2 and carefully weigh the bag. Unstopper the flask and monitor the weight of the bag. The weight will increase thus apparently violating the law of conservation of matter. However, the mass (a measure of the amount of matter present) did not change, only the weight changed. As the CO2 reacted with NaOH the volume of the bag decreased thus decreasing the buoying effect of the air around the bag and making its apparent weight increase.
t) All of the contents of a coke can can be placed in the nipple of a baby bottle! Warm the bottle with hot water. Pour the contents of the coke can into the bottle and rapidly seal the bottle with the nipple (a nipple without a hole must be used). Pour the contents back and forth and warm the bottle when the effervescence stops. Eventually the CO2 pressure will expand the nipple enough to allow the entire contents to fit into the nipple.
u) Transport of CO2 through soap films. Blow up several soap bubbles with CO2 and place them into a container filled with CO2 using a wand designed for blowing bubbles. The bubbles will grow in size. Take them out of the container and they will shrink. The increase and decrease can be carried out several times before the bubbles break.
Plant Capillary Action - Obtain a white rose or white carnation with a short stem. Carefully slice the stem lengthwise leaving about a half inch of the stem intact below the flower. Put about 50 drops of red food coloring in one test tube and 50 drops of blue food coloring in another test tube. Add water to each test tube and place the split stem ends one in each test tube. Make sure the end of each stem slice is below the water level. Fasten the flower to a ring stand or other object to keep it from tipping over. After a few hours to 24 hours the flower will appear red on one side and blue on the other. The two stems will also be very deep red and deep blue respectively. This experiment demonstrates that water is taken up a plant stem by capillary action.
Effect of Salt on Boiling Point - Put 100 mL of water in a 250 mL beaker along with a boiling chip. Suspend a thermometer in the water so that it does not touch the bottom or the sides of the beaker. Heat the water with a bunsen burner until it is vigorously boiling. Then record the boiling point after it has boiled for at least a 3 minute period. Then take a second 100 mL aliquot of water, dissolve 10 g of sodium chloride into the water and repeat the experiment described for water alone. Calculate the number of moles of NaCl used. Then take a third 100 mL aliquot of water, dissolve 17 g of sodium bromide into the water and repeat the experiment. Calculate the number of moles of NaBr used. Is there a relationship between the boiling point elevation and the number of moles of impurity dissolved in the water which is independent of the impurity.
Blue Bottle Experiment - A blue solution is mixed with a colorless solution and in a few minutes the blue solution has turned colorless. It remains colorless but when shaken it immediately turns blue. If allowed to sit for another 2-5 minutes it turns colorless again. Shaking again returns the blue color.
Why does the solution turn colorless?
Why does shaking regenerate the blue color?
The students will eventually come up with the following explanation:
The blue material is destroyed by something in the solution and the shaking mixes oxygen (from the air over the solution) with the solution and the oxygen reforms the blue material. This can be tested by bubbling carbon dioxide through the solution to remove all of the air. If the above explanation is correct, shaking with carbon dioxide should not regenerate the blue solution. Bubbling air through the solution should then regenerate the blue color as it displaces the carbon dioxide. A carbon dioxide generator can be prepared by placing a tablespoon of baking soda (sodium bicarbonate) and an equal volume of powdered alum in a flask equipped with a rubber stopper fitted with glass tubing. When just enough water is added to cover the chemicals, carbon dioxide evolution begins immediately and should last for more than 5 minutes. If gas generation slows down, add a little more water. Dissolve a few small crystals of methylene blue into 150 mL of water. This should be done the day before and be sure not to add too much methylene blue. It must all be dissolved for the experiment to work. The solution should be a light blue color. Dissolve 5g of potassium hydroxide in 100 mL of water. When you are ready to start the experiment add 3g of glucose to the methylene blue solution and then add the 100 mL of potassium hydroxide solution to the methylene blue solution and mix well. After a few minutes the blue solution will turn colorless. Shaking regenerates the blue color.
Bernoulli Effect
a) Blow along the top edge of a piece (about 3" x 6") of thin notebook paper. The paper will straighten out flat with the paper moving toward the side you are blowing across.
b) Place a straight pin through the center of a playing card. Drop the pin into an empty thread spool so that the card lays flat with the pin through the hole in the spool. Hold this assembly with the card down and blow into the other end. You can release your hold on the card and it will not fall until you stop blowing.
c) Place a ping pong ball in a funnel and blow through the stem of the funnel. You can't blow the ball out of the funnel.
d) Tie two small plastic boats to separate strings and place the boats in a sink with the strings taught and tied to a weight on the edge of the sink. Direct from a hose a stream of water between the two boats. The boats will rapidly move together.
e) Drill a small hole in a ping pong ball and then screw a small screw into the ball and tie a piece of string to the screw. Hold the string sand slowly bring the ball into a fast stream of water from a faucet. The ball will be drawn into the water stream and you will have to tug on the string to get the ball out of the stream of water.
f) Drill a small hole in two ping pong balls and then screw a small screw into each ball and tie a piece of string to the screws. Suspend the balls from a bar so that they are about two inches apart. Direct a stream of air between the balls with a straw and the two balls will move together.
g) Turn a hair dryer on the highest blower setting with the lowest heat and direct the air stream up at an angle of 90 to the floor. Suspend a ping pong ball in the stream. The ball will remain in the stream and not fall to the floor. Slowly move the air stream away from the vertical. The ball will remain in the stream until the angle is less than 45.
h) Place a glass tube (roughly vertical) in a beaker of colored water. Place a second glass tube at a right angle to the first tube so that the ends of the two tubes are close together. Blow through the horizontal tube and observe the water level in the second tube. This is the same principle used in an atomizer.
i) Place an 8" x 5" note card on top of a book. Demonstrate how easily you can blow the card off of the book. Now place the same card on top of two books spaced 10 cm apart so that the card just overlaps each book. Kneel down and blow on the card from the top, bottom or end on. No matter how hard you blow, the card can't be blown off of the books.
Archeomagnetism - Whenever a camp fire occurs the soil under the fire is superheated to the point where iron particles in the soil are floated and thus becomeoriented with the earth's magnetic field. The earth's magnetic field varies constantly and the magnetic north pole moves around almost continuously. The position of magnetic north has been determined accurately for the past 2,000 years. Archeologists are thus able to date camp fires to within a 10-15 year period. This has been particularly valuable for dating the inhabitation of the Anasazi ruins of the American southwest.
Density of Floating and Sinking Objects Using only Water Displacement
a) Density Less than 1.0 - An object whose density is less than 1.0 will float in water. Take a two-liter coke bottle and cut the top of the bottle off just below the slopped top. Drill a hole in the side of the bottle (1/4" in diameter) about an inch below the top of the bottle. Glue a plastic straw in this hole using a glue gun or better using plastic epoxy. The straw should be nearly flush with the inside of the bottle and protrude about 1" out and slightly downward. Fill the bottle with water until the water begins to run out of the straw. When the water stops running you are ready to use it. Gently place a floating object in the bottle and measure the water displaced by catching the water as it flows out of the straw. The weight of the water displaced is equal to the weight of the floating object. Since the density of water is 1.0, the volume of the water displaced will give you the weight of the object in grams. Now push the object just below the surface and measure the additional water displaced. Add this to the original water displaced and you have the volume of the object since the volume of water displaced by a submerged object is equal to the volume of the object. Since density = mass/volume, and you have both mass and volume, the density can be calculated.
b) Density Greater than 1.0 - An object whose density is greater than 1.0 will sink in water. Using a two-liter coke bottle with an added side tube (described above) you can easily measure the amount of water displaced when the object is submerged in water. The volume of the water displaced is equal to the volume of the submerged object. However, in order to calculate the density of this object you would also need its weight. This could be determined using a balance but most elementary classrooms do not have balances. Remember that the weight of any object that floats in water is equal to the amount of water displaced when it is floated in water. Thus, the key is to get this object to float. How can we do that? Simply put the object in boat! You can use a salsa container from El Pollo Loco or any similar shaped piece of plastic or wood shaped as a boat. Fill the two-liter coke bottle almost to the side hole, place the empty boat into the water and then fill the bottle until the water runs out of the side hole. When the water finishes running out, put the object in the boat and catch the displaced water. The weight of this water will be equal to the weight of the object!
Density - Students know about density just from their experiences with water. For example a round rock will sink in water but a rubber ball of the same size will float in water. They need to learn about density being a weight per unit volume rather than an object being just "heavy" or "light". A very large wooden block is less dense than a small piece of steel even though the wooden block actually weighs a lot more than the small piece of steel. If the two pieces were the same size then the steel object would be much heavier.
a) Egg Density - Place a fresh egg in a small glass of water and note that it sinks to the bottom. Slowly add salt to the water until the egg just rises to the top. If the same egg is then boiled and allowed to cool completely submerged under cold water, it will now sink when placed in the same salt water solution. (The cooling egg sucks water into the egg and increases its density.) Rock salt, Kosher salt, or pickling salt (available in grocery stores) all work better than table salt because table salt has some water insoluble additives which cause the water to be very cloudy. Adding salt to the water increases the density of the water and allows the egg to float. Most students have seen this demo. Ask them if adding sugar will make the egg float. Most will say no; but sugar works just as well! A good demo is to cause the egg to float by adding sugar and then cause it to sink again by adding rubbing alcohol.
b) Coke Density - Float a can of Diet Coke and regular coke in a large glass container. The regular coke sinks but diet coke floats. A diet Coke is less dense than the regular Coke because the regular Coke has about 200 times as much added sugar (by weight) as the diet Coke has added aspartame (NeutraSweet). Aspartame is about 500 times sweeter (wt. for wt.) than table sugar (sucrose). Since all else is approximately equal in the two cans we see that the diet Coke is less dense. A very revealing demo is to put a regular Coke on one pan of a two pan balance and a Diet Coke on the other pan. Then add sugar to the Diet Coke side until the balance. It takes about three tablespoons of sugar. There is 38 g of sugar in a can of regular Coke. Another good experiment is to have the kids weigh a piece of gum, then chew it for 10 minutes, and then weigh it again. The lost weight is all sugar. Then they can do the same experiment for sugar free gum..
c) Can We Say That Heavy Objects Are More Dense Than Light Objects? - Compare two objects of different density in which the light object is actually the denser object. A large cork stopper and a small rubber stopper work well. The heavier object, the large cork stopper, will float on water but the lighter object, the rubber stopper, will sink. Then show that a rubber stopper the same size as the cork stopper is actually much heavier. You can also use a large hollow metal ball and a small solid piece of the same metal. The big ball will weigh much more than the small piece of metal but the ball will float and the solid metal piece will sink. These activities will help the students to see that density is weight per volume and not just weight or volume.
d) Sink and Float with plastic Easter eggs - This activity uses two small plastic eater eggs which float in water. As you add metal washers to the eggs they sink lower in the water until finally the egg sinks. Now put the same number of washers into a large plastic egg and it easily floats. It now takes a great many additional washers to sink the big egg. The students will see that sinking and floating depends on the size (or volume) as well as the weight of the object.
e) Buoyancy. Hang an object of less than one kg from a 1 kg spring scale. Note the weight. Slowly raise a beaker of water so that the object is covered with water. There will be a decrease in the observed weight of the object due to the buoyant force of the water.
f) Clay Boats - A ball of clay will sink in water but if shaped into a boat it will float. See how many metal washers your students can float in the boat by changing the shape of the boat.
g) Hardware Store Density - Get similar shaped objects from a hardware store that are made out of different plastics and metals such as straight pipe, elbows, etc. Pass them around the class in a box so students can see the difference in density.
Household Density Column Into a 25 x 200 mm test tube add 10-20 mL of each of the following household chemicals by carefully pouring them through a long stem funnel into the tilted test tube. They must be added in the following order (from the most dense to the least dense):
1) Clear Karo Syrup
2) Aunt Jemima Syrup (brown)
3) Methylene Chloride based Paint Stripper (clear)
4) Antifreeze (green)
5) Dawn Dishwashing detergent (blue)
6) Flex Shampoo (white)
7) Water (with red food coloring)
8) Vegetable Oil (clear to pale yellow)
The above will need to be a teacher demo because of the toxic items above. However, the students can use other mixtures such as the set below:
Karo Syrup
glycerine
salt water (16 oz of water and 5 tbsp of Kosher salt plus food coloring)
Dawn Dish soap
water with food coloring
vegetable oil
rubbing alcohol with food coloring
A nice exercise is to have the students determine this relative density order by mixing together only two ingredients at a time. This can be done by slicing a potato to make a base and then pushing straws into the potato followed by adding the liquids to the straws two at a time to determine the relative order of densities. When they think they know the order, they then put them all in one straw.
Inertia
a) Orange Whap. Place a thin piece of wood or particle board on top of a large, heavy ceramic cup with about an inch protruding over the edge of the cup. Put the cup at the edge of a table so that the wood protrudes over the edge of the table but the cup does not. Place an orange on top of the board and then strike the board sharply by slapping a yard stick against the board. Be careful that the yard stick only hits the board and not the cup. The edge of the table will keep the yard stick from striking the cup. You can also use a broom. Bend the bristles over and stand on the broom. Releasing the broom handle will send the handle crashing into the side of the table. The board will fly out and the orange will drop into the cup. The inertia of the orange keeps it from moving with the board.
b) Egg Whap - Place a shallow pie tin on top of three wide mouth glasses filled with water. Then place three toilet papers rolls on top of the pie tin exactly over the center of the three glasses. Finally place eggs on top of each toilet paper roll. Use the broom handle method described above to "whap" the edge of the pie tin. The pie tin will fly across the room taking the toilet paper rolls with it and allowing the eggs to drop into the water unharmed!
c) Hammer Pull. Place a hammer on end on top of a piece of cardboard to which a piece of string is attached. Quickly jerk the string and the card board comes out but the hammer does not fall.
d) Plastic loop and Al foil. Cut a two inch section out of a 2-liter plastic coke bottle and place it on top of a wine carafe. On top of the plastic loop place a wadded up piece of Al foil. Striking the loop on the outside sends the Al foil flying but striking the loop on the inside allows the foil to drop into the carafe.
e) Golf Ball Drop. Drop a golf ball while walking slowly across a room. The golf ball follows you across the room.
f) Coat Hanger and Weights. Fashion a metal coat hanger into V shape with long side arms. Suspend heavy weights from the end of each side arm. Place the V on your head and rapidly turn around. The coat hanger/weight system will not move.
g) Heavy weight suspended from string with a second string hanging down. If the bottom string is pulled with a sharp jerk, the bottom string will break. If the bottom string is pulled with a slow, steady force, the top string will break.
h) Pie Plate Hover Craft. Drill a 1/4 inch hole in the bottom of a metal pie plate and glue a thread spool over the hole. Place a balloon over the spool and blow up the balloon through the hole in the bottom of the pie plate. The plate will glide over the floor on a bed of air when shoved lightly.
i) Basketball Shoes vs. Dress Shoes. Measure the amount of force it takes to pull a shoe across a table using a spring scale. Put one shoe from each of two pairs inside each other so that the weight of the pulled shoe assemblies are the same. The students can investigate which sole patterns are most effective at producing friction. (Remember that more force is required to get the shoes moving then to keep them moving.)
j) Potato and Straw. A straw can easily be pushed through a potato if you stab the straw rapidly but if you push slowly the straw will crumple and not go through the potato.
k) Ball Bearing Path. Watch the path of a ball bearing as it exits the end of a curved tube.
l) Ping Pong Ball on String. Drill a small hole in a ping pong ball and attach a two foot length of kite string. Swing the ball by the string and let go of it. The ball will continue in a straight line in the direction it was going at the moment of release.
Lenz's Law, Cow Magnets, and Neodymium Magnets
Obtain a six foot length of cooper tubing approximately 5/8 to 3/4 inches in diameter but wide enough for your cow magnet to easily slide through the tube. Measure the amount of time it takes your cow magnet to fall six feet. This will be less than 0.5 seconds. You could also measure the time required for your magnet to fall through a plastic sprinkler pipe of the same diameter so that friction would be the same. Note that copper is not magnetic. Now drop the magnet down the copper tubing and measure the amount of time it takes to come out the other end. It takes about 2.0 seconds for this to fall through the copper tube but that will vary. The stronger the magnet the longer it will take to fall through the copper tube. Now try two neodymium magnets placed together (they are sold in packets of two). It now takes 12 seconds for the magnet to fall through the copper tube. In that amount of time a free falling object would have fallen over 2200 feet (distance = (1/2)(9.8 m/s2)(t2). One of these small magnets takes about 6 seconds. I haven't tried three or four but that would be interesting. The explanation is Lenz's Law which states that a moving magnet field will generate a moving electric field in an adjacent wire (or pipe in our case). This moving electric field generates a moving magnetic field in the wire which will oppose the original magnetic field.
Blue Sky and Red Sunset
Obtain a transparent glue stick like the ones used in glue guns. They are about 3 inches long and 1/2 inch in diameter. In a darkened room place the glue stick vertically on the end of a bright flashlight with only enough of the light exposed to just cover the end of the stick. Turn on the flashlight and you will see the whole range of scattered light colors from blue at the end of the light to red at the other end. The particles in the glue stick scatter the light with the blue easiest to scatter and the red the hardest to scatter.
Forced Vibration
Take a metal coat hanger and bend the hook so that it is straight and perpendicular to the bottom of the coat hanger. Hang the coat hanger from a piece of thread and bang it with a pencil and you will hear a faint sound. Now stick the coat hanger with the straight end in a piece of high density polysytrene (the kind used to protect electronic equipment during shipment). Now bang the hanger with a pencil and note the loud sound. You have forced the polystyrene to vibrate at the same frequency as the hanger and thus amplified the sound.
How Can Molecules Pass Through Cells?
All animals must transport oxygen from their surrounding environment to their cells and transport carbon dioxide waste from the cells back to the environment. For most animals this environment is the air but in fish the environment is water. Large land animals have lungs to obtain oxygen from the air while fish have gills which extract the oxygen from the water as it passes through the gills. Grasshoppers have a row of small holes, called spiracles, on the bottom of their body through which oxygen passes. Still other animals like worms and jellyfish merely absorb oxygen directly through their skin. How can these molecules of air and carbon dioxide pass in and out of the cells of animals?
The following experiment clearly illustrates that small molecules can pass through cell walls. Take a small plastic bag and add to it 100 mL of water and a few drops of iodine solution. Carefully seal the bag and make sure that it does not leak. Place the bag in a large jar half filled with water. Then obtain a strip of white writing paper (or construction paper) and hang it over the edge of the jar so that half of it is in the water. Then seal the jar. After about an hour the writing paper will become blue at the interface between the water and the air. After two days the paper will be dark purple. Clearly the iodine went through the walls of the bag in much the same way as oxygen can go through cell walls.
The writing paper will become blue because the surface of the paper is coated with a thin film of starch to make it smooth. Starch reacts with iodine to give a deep blue-black complex. You should test the paper first with a drop of iodine to make sure it turns blue-black. You might compare this to a piece of newspaper which does not have starch on its surface. The iodine will not change color when in contact with the newspaper.
Momentum
a) Ping Pong Ball on Top of Golf Ball. Drop (from a few inches) a golf ball with a ping pong ball on top. The momentum of the two balls is transferred to the ping pong ball.
b) Vampire Killer. Take a heavy metal rod (2-3 inches in diameter and weighing at least 20 pounds) and place it against your chest. A second person can strike the end of the rod with a hammer and you will not feel the blow.
c) Newtonian Swing - Five balls hanging from a central rod can be used to illustrate the conservation of momentum as well as the conservation of energy.
d) The Egg Toss - This demo illustrates the fact that if you increase the amount of time required to stop an object, you will need less force to stop the object. We all use this principle every time we stop our cars at a stop sign. Have two people hold a bed sheet so that it makes a trough. You can then throw a fresh egg at the sheet as hard as you can and the egg will drop unharmed into the trough after hitting the sheet.
Angular Momentum.
a) Swivel Chair. Sit in a swivel chair with your arms held out and a heavy weight in each hand. Spin the chair and slowly bring your hands in to your chest. Your spinning speed will dramatically increase.
b) Two Weights on a String. Tie a small and a large one-hole rubber stopper at each end of a three foot long string threaded through a six inch piece of PVC 1/2 inch pipe. Start swinging the larger weight at a constant speed. Now pull on the smaller weight and the larger weight will spin faster and faster as the radius of its swing becomes smaller.
25) Falling Objects
a) Drop a piece of paper (held horizontally) and a golf ball simultaneously. The golf ball will hit the floor well before the paper. Now turn the paper vertically and the two objects will hit the floor almost at the same time.
b) Drop a piece of paper and a piece of wood of the same size with the paper on top. They will both hit the ground at the same time.
c) Drop a heavy weight and a light weight held by finger tips. The light object will usually land first because it is harder to let go of the heavier object.
Weightlessness
a) Falling Cup Demo. Weights and rubber bands attached to cup. See hand out.
b) Water Drop. Drill a small hole in the bottom of a large plastic cup. Drop the cup as you take your finger off the hole. Water does not run out of the cup while the cup is in free fall.
c) Water Bucket. Fill a bucket half full of water and swing it over your head. The water does not come out.
d) Elevator and Scale. Stand on a bathroom scale in an elevator that accelerates rapidly. You will notice that your weight increases by 10-20% as the elevator goes up and it decreases by 20-30% when the elevator goes down. You only see the weight change while the elevator is actually accelerating or decelerating. The greater the acceleration the greater the weight change.
Vertical and Horizontal Motion.
a) Two Golf Balls. Gently throw one golf ball horizontally while simultaneously dropping a second golf ball from exactly the same height. They will hit the ground at the same time.
b) Two Coins on a Note Card. Fold a note card so that it has a V in the middle. Place a coin on each side and extend the card over the edge of a table. Hold the end of the card on the table and flick the V extending over the table with your finger sending one coin flying across the room and dropping the other coin at the same instance. They will strike the ground at the same time. You can also use a ruler with a piece of note card tapped to each side of the ruler to hold the coins.
Newton's Third Law
a) The Water Rocket - This demo actually illustrates Newton's Third Law of motion: For every action there is an equal and opposite reaction. Fill a 2 liter plastic coke bottle 1/3 full of water. Place a #4 rubber stopper (available at hardware stores) which has a sports needle pushed through it, tightly in the bottle. Attach a tire pump to the end of the sports needles and invert the bottle into a launching pad (a couple of 6 inch 2 x 4's with a piece of plywood nailed on top and a "U" shape cut out to hold the bottle). Pump air into the bottle until the systems blows out the stopper. The bottle will go as high as an 8 story building.
b) Hero's Engine - Obtain a small can (1-2 cups) with a screw cap in the center of the top (an old brake fluid can works well). Attach a fishing line swivel to the exact center of the cap. Make sure that the can lid does not leak. Using an ice pick jab three holes evenly spaced around the side of the can (about 3/4 of the way up the side of the can). Before pulling the ice pick out bend the pick almost parallel to the side of the can. Place about 20 mL of water in the can and then heat it to boiling. The steam pressure will come out of the holes and rapidly spin the can. This demo illustrates boiling, change of state, steam pressure, and Newton's third law (for every action there is an equal and opposite reaction). An even simpler version uses a soda can with the flip top bent up. Tie a nylon fishing line to the flip top and proceed as above.
Pressure
a) Effect of Depth and Volume on Water Pressure - The following experiment clearly illustrates the fact that the pressure exerted by a body of water is proportional to the depth of the water and not to the volume of the water. Obtain a large Crystal Geyser bottle, a 1 gal Arrowhead Water bottle, and a two liter soft drink bottle. These three bottles are approximately the same height but vary considerable in their width. Drill a 1/8 inch hole in each bottle three inches from the bottom. Cover each hole with a piece of Scotch Tape and then fill the bottles with water so that the depth of the water in each bottle is the same. Quickly remove each piece of tape and allow the water to flow out of the bottles. (It is important that the holes do not have any pieces of plastic flash sticking to them. This will change the direction of flow of water and make the demo inconclusive.) Notice that the distance traveled by each stream of water is exactly the same indicating that only the depth of the water is important and not the volume of the water
b) Pressure is Force x Area - Consider the effect on your toe if a woman wearing a spike heal steps on you're toe compared to a woman wearing flats. You are walking with a friend on an ice covered pond. Suddenly, the ice begins to crack. Your friend begins to run and falls through the broken ice. You purposely lie flat on your stomach and begin to pull your self toward to side of the pond by moving your hands and legs in a swimming fashion. You make it safely to the side. Explain why you made it safely to the edge but your friend fell through into the icy water.
Center of Gravity -
a) Balancing Rod - Try to balance a large cork stopper with a wooden rod protruding about two inches from the cork. This can't be done because the center of gravity of the cork/wood system is too high. Now place two forks into the cork pointing down and on opposite sides of the cork. The system can now be easily balanced on the wood rod because the center of gravity is below the end of the wood. If the wood rod has a groove in it you can balance the system on a long piece of thread held by two students and slide the assemblage along the thread.
b) Balancing Ruler - Balance a horizontally placed ruler from the end of the ruler by attaching a string loop which can hold a hammer against the ruler. The hammer to ruler angle will be about 30 . The head of the hammer must extend slightly beyond the end of the ruler with the other end of the hammer resting on the ruler.
Phases of the Moon and Eclipses
Use a shop light suspended from the ceiling at one end of a darkened room as the sun and a solid white ball as the moon. Have the students stand in the middle of the room (they are observers on the earth) and walk around the outside of the room holding the ball up high. The students will observe the phases of the moon. Now use the white ball as the earth and use a baseball as the moon. Eclipses are easily observed by holding the moon between the sun and the earth for a solar eclipse and holding the earth between the sun and the moon will show a lunar eclipse.
Machines
Raise Teacher with your Finger. Work out equals work in. Use a long board and a brick to illustrate that force times distance at one end of the board equals force times distance at the other end. Moving the fulcrum changes the force needed to raise the teacher.
Conservation of Energy
Tie a heavy weight on the end of a long rope suspended from the ceiling. Pull to object up to the level of your nose and let go of the object. The object will return to a spot in front of your nose due to conservation of energy and lose of energy due to friction. Be careful not to push the object when you let go of it or it will hit your nose!
Heat and Heat Transfer
a) Hot Molecules Move Faster - Fill one 600 mL beaker with hot water and a second 600 mL beaker with ice-cold water (strain off the ice). Add a drop of food coloring to each beaker. The color spreads very quickly through the hot water but the color just falls to the bottom in the ice water and mixes very slowly.
b) Hands in Hot and Cold Water - Prepare four beakers of water. Fill the first with ice water, the second and third with room temperature water, and the fourth with hot water (but not hot enough to burn your hand). Now place one hand in the hot water and one hand in the cold water for about 15 seconds. Now put each hand in one of the beakers containing room temperature water. The hand which was in the cold water now feels warm and the hand that was in the hot water now feels cold. Heat rapidly flows out of the warm hand into the room temperature water. The loss of heat from the warm hand causes that hand to feel cold. Heat rapidly flows from the room temperature water into the cold hand. Thus gain in heat makes the cold hand feel warm.
c) Paper, Metal and Flame - Tightly wrap a piece of paper around a cylinder of brass or steel so that you can hold it by the paper. Then place the part of the paper touching the metal into a candle flame. It will not burn because of the heat transfer from the paper to the metal. Then remove the paper from the metal and place it back in the candle flame. It will burn immediately.
d) Paper, Strainer and Flame - Hold a small rolled-up piece of paper in a long tweezers and place the paper over a candle. The paper immediately bursts into flame. Now place an identical piece of rolled-up paper in a metal strainer. Place the strainer of the flame so that the flame touches the paper. It takes a very long time for the paper to ignite due to the excellent heat transfer properties of the metal strainer.
e) Steel and Plastic Pipes - Grasp a 6" steel pipe in one hand and a 6" plastic pipe in the other hand and note what you feel. The steel pipe will feel quite cold while the plastic pipe will feel room temperature. Your hand is about 30 F hotter than the two pipes which are actually at the same temperature. However, since steel is a good conductor of heat, the heat rapidly leaves your hand toward the cooler steel pipe and your hand feels cold. The plastic pipe is a poor conductor of heat so heat does not leave your hand and the plastic pipe feels room temperature.
f) Heat Race Trick - Cut one piece of 16 gauge copper wire to 6" length and then cut two 3" length pieces. Push the 6" piece through a cork stopper and push both 3" length pieces into a second cork stopper. Then hold one end of the two-piece apparatus in your hand while placing the other end in a flame. Have a student try the same with the one-piece apparatus. Instruct the student to drop it when it gets hot. Yours will burn the cork before the second wire ever gets hot. The metal wire is very good at heat transfer but the cork will not transfer the heat from the first wire to the second wire.
g) Burning Handkerchief - Soak a handkerchief in 50 % rubbing alcohol/50 % water and then wring it out. Dry your hands and put away the alcohol. Then hold the handkerchief with a metal tongs, turn out the room lights and light the handkerchief with a long fireplace match. Hold the burning handkerchief up for about 10 seconds and then plunge it into a bowl of water, turn on the room lights and show that the handkerchief has not burned. Heat transfer occurs from the hot handkerchief to the water preventing the burning of the handkerchief.
h) Boil Water in a Paper Cup - Water can be boiled in a paper cup filled with water and the cup will not be burned or charred. The cup must have a flat bottom without a lip or the lip will burn. The cup should be filled nearly to the top so that the top of the cut does not burn.
i) Two Balloons and a Match - Inflate a round balloon with air and tie it off. Fill a second balloon with 60 mL (1/4 cup) of water and then inflate it with air to equal the size of the first balloon. Light a match and hold it under the first balloon. The balloon breaks immediately perhaps even before the match touches it. Now light a second match and hold it under the second balloon. The balloon does not break due to the heat being absorbed by the water. Relate this experiment to car radiators, the moderating effect of oceans on the temperature of land areas near the water, time needed to boil water (the "watched pot never boils"). It takes ten times as much heat to raise 1.0 gram of water 1 than it takes to raise the temperature of 1.0 gram of iron 1.
Expanding and Contracting Air
a) Cloud Chamber - Add a cup of warm water to a large flask or bottle. Turn the bottle on its side and insert a burning match in the bottle using a tweezers (or you can use a long fireplace match). Allow the match to burn for about 20 seconds and then extinguish the match and allow the smoke to stay in the bottle. Attach a bicycle pump to the flask by pushing a sports ball needle through a tight fitting rubber stopper. Pump about 5 or 6 times and then release the pressure by loosening the stopper. The expanding gas will cool and thus condense water vapor to cause clouds to appear. The water will condense on the smoke particles making a dense fog. If you then pump up the pressure again the clouds will disappear. Compressing gas causes it to heat which will vaporize the water droplets and the clouds disappear. This cycle can be repeated many times. This experiment illustrates the fact that a low pressure front will mean cloudy skies and possibly rain, while a high pressure front will mean clear skies. There needs to be dust particles in the air in order to have cloud formation. That is the reason for cloud seeding to make rain. The smoke particles serve this purpose in the demonstration.
b) Warm and Cool Air - Place your hand close to your mouth but not touching. Blow your breath onto your cupped palm with a wide open mouth. Your breath feels warm. Now purse your lips to make a small hole and blow your breath onto your cupped hand. Your breath now feels cool. Once again, expanding air cools.
c) Tire and Expanding Air - Release some air from a tire and the air will feel very cold because it is expanding and cooling.
Relationship between Wavelength and Frequency (Pitch) -
Fill a deep waste basket with water and immerse a four foot long, 3-4" diameter aluminum pipe in the water. Sound a tuning fork and place it about an inch above the pipe opening. Raise and lower the pipe until the sound of the tuning fork is greatly amplified. The distance from the fork to the water is proportional to the wavelength of the tuning fork. Use forks of lower and higher frequency and see if the wavelength is lower or higher. Wavelength is inversely proportional to the frequency (or pitch) of the sound.
Take a 3' long piece of dryer or water heater vent pipe (these are 3" or 4" in diameter) and wedge two pieces of brass screen wire about 1/5 of the way up the tube. (you can also fasten the wire with a screw to make the placement more permanent). Heat the brass wire with a propane torch getting as much of it red hot as possible. Remove the torch and hold the tube vertical. It will make a very loud fog horn sound. Using longer or shorter tubes will give lower or higher pitch.
Series and Parallel Wiring. Cut six bulbs from a miniature Christmas light set (You can easily obtain an old set from a student, friend, etc.). For each bulb leave about 4 inches of cord on each of the two leads. Use a nine volt battery to light the bulbs (two flashlight batteries in series also works and is cheaper but the lights will be 1/3 as bright). One Christmas tree light set can provide enough sets of three bulbs for a your whole class to work in pairs. The use of a nine volt battery makes the experiment completely safe. The demo clearly shows why houses are wired with parallel circuits.
Combustion
Combustion Needs Oxygen to Proceed. Place five upright candles of varying length in a small aquarium, battery jar or similar transparent container. Make sure that the tallest candle is well below the top of the container. Sprinkle about a 1/4 pound of baking soda on the bottom of the container, light the candles and then slowly pour in vinegar. Carbon dioxide will be rapidly produced. Since CO2 is heavier than air it will fill the container from the bottom up as the oxygen is forced out. The candles will go out in order from lowest to highest candle. Relate this experiment to CO2 fire extinguishers. The CO2, which is heavier than air, forms a blanket over the fire. This prevents oxygen, which is needed for the fire to burn, from reaching the fire. Also, the CO2 gas generation can be related to the use of baking soda for an upset stomach from eating too much food. The excess stomach acid generated when you eat too much is destroyed by the baking soda with the generation of CO2. Thus taking baking soda makes you belch. You can also include a simple gas density experiment. Blow some soap film bubbles and watch as they slowly fall to the floor. Then blow additional bubbles so that they fall into the above transparent container filled with CO2. The bubbles float because they are less dense than CO2.
Paper Chromatography - Spot three different colored marking pens about 1 cm from the bottom of a piece of absorbent paper. A coffee filter paper works very well. (The paper is stapled together in a tube fashion). Place the filter paper tube in a developing jar which contains 0.1 % sodium chloride solution. Make sure the solvent does not directly touch the ink spots. Cover the jar either with a screw cap or just place a piece of aluminum foil over the jar. The developed chromatogram will separate all of the dyes from each ink in about 10 minutes.
Effect of Temperature on Reaction Rate - Put ice water, room temperature water, and warm water in three bottles with tubing leading out of each jar. Set up a system to collect any gas generated individually from each bottle. Lead a piece of rubber tubing from the bottle to an inverted graduated cylinder filled with water and resting in a bowl filled full of water. The carbon dioxide gas will displace the water. Carefully measure the amount of time required to generate 50 mL of CO2 gas from each of the three flasks by dropping one Alkaseltzer tablet separately in each flask. The time required dramatically decreases as you raise the temperature. Alternatively you could just visually watch the rate of bubble formation as a function of temperature.
Light
a) Sunset and Blue Sky - Shine a strong beam flashlight through a glass of water so that the beam hits the ceiling in a darkened room. Now add a few drops of non-fat milk to the water and stir. Look at the color of the light coming out of the side of the glass and the color of the light beam . Add more milk with stirring and carefully investigate the colors observed from the side of the glass and the color of the beam itself shining on the ceiling. Milk is a colloidal suspension. The blue light is scattered so that the solution appears blue from the side. (Similarly the molecules in the earth's atmosphere scatter the blue light making the sky blue.) The emerging light beam becomes more orange as you add milk because the blue light has been scattered away. (Similarly the blue and yellow light of the sun is scattered away at sunset by the dust and smog in the atmosphere making the sun appear red.)
A simpler and less messy method uses a 3 inch glue stick (the kind used in glue guns) jammed into a hole drilled into the center of a piece of card board or metal sheet. Place this on top of a bright flashlight and view in a darkened room. The glue stick is blue at the bottom, orange in the middle and red at the top. To make it more permanent glue the car board or metal sheet to the top of the flashlight.
b) Refraction (Bending) of Light - Glue a penny into the bottom of a can approximately three to four inches deep and three to four inches wide. Adjust your line of site so that the penny in the bottom of the can is just not visible. Have some one else pour water into the can while you hold still. The penny can now be seen.
Polymers
Sterno - Place 20 mL of saturated calcium acetate, Ca(C2H3O2))2, solution in a 250 mL beaker. Add 200 mL of 91% isopropyl alcohol (rubbing alcohol) to a second 250mL beaker. (Ethyl alcohol (95%) works well also but is not as readily available.) Pour the alcohol into the calcium acetate solution. The mixture immediately gels to form Sterno. You can light the gel and it will burn with a faint blue flame for several hours leaving a small amount of white ash.
Slime - Place 20 mL of 4% poly(vinyl alcohol) solution in a paper cup. Add 3 to 5 mL of4% sodium borate solution. Using a circular motion, stir vigorously with a stir stick. As the solution begins to solidify, continue to stir. When a gel has formed, remove it and continue to shape it with your hands. Sources of Chemicals: The polyvinyl alcohol must be highly hydrolyzed (90-100%). Good sources are: Kodak, Cat. No. 153 9709. You can reach them at (800) 225-5352; Triess Science in Burbank, (818)247-6910, Cat No. CP27; Flinn Scientific, (800)452-1261, avaiable both as the solid and a 4% solution ready for slime formation. The sodium borate is just Borax which is available in any grocery store.
Static Electricity for Less
a) Electrophorous (a device for transfering charge) - Tape a piece of audio tape around the top edge of a pie plate (the tape may be omitted but it works better with the tape). Then tape a styrofoam cup upside down in the middle of the pie plate for use as a handle. Tape a sheet of styrofoam on a table top and briskly rub it with a piece of wool. This causes the foam to become negatively charged. Place the pie plate on the foam and touch the edge of the plate briefly with your finger while the plate rests on the styrofoam. Raise the plate off of the styrofoam and you have a negatively charged electrophorous.
b) Capacitor (a device for storing electrical charge) - Take two clear plastic drinking cups and glue aluminum foil cupcake holders on the bottom of each. On one of the cups glue a strip of aluminum foil 5 cm wide and long enough to extend from the bottom 3-5 cm above the rim of the cup. The cup with the aluminum foil will be the inner cup. Nest the cups together as shown above. Charge the inner cup (via the aluminum foil lip) with the electrophorous. Simultaneously touch your thumb and index finger of one hand on the aluminum foil of both cups and feel the discharge of electricity.
c) Pith Ball (A charge detector) - Attach a flexible straw to the outside of the cup. The flexible part is at the top of the straw. Bend the flex portion downward to form a 45 degree angle. Secure it with tape. Roll a small piece of aluminum foil into a small ball and attach the ball to a piece of thread with a knot. Tape the other end of the piece of thread to the straw with tape.
d) Scotch Tape Charges - Take two equal length pieces of scotch tape and place them back to back. You should see no attraction or repulsion. Tape one of the pieces to a wooden table top, rub it with your finger, release it from the table and note how it will strongly attract the second piece (again, back to back). Then place both pieces of tape on the table and rub both. Upon removal from the table these pieces will strongly repel each other (always back to back). Tape two pieces of tape on the table. The top piece should be marked T and the bottom piece marked B. Pull these two pieces of tape from the table and note that they attract each other (again back to back). Also try two T tapes and two B tapes. Note that although two T tapes or two B tapes repel each other, they are attracted to any uncharged object.
e) Humid Weather Static Electricity - The following simple device can be used to illustrate static electricity even in damp and rainy weather. The materials needed are a straw, Scotch tape, a pin, and two small pieces of aluminum foil. Cut a small V-shapedwedge out of the middle of the straw and fold the straw at this V to a 90 to 120 angle and scotch tape the straw at this angle to hold it rigid. Roll up two small balls of aluminum foil about 1/2 inch in diameter leaving a small handle protruding from the ball. Scotch tape the balls via their handles to the ends of the straw. Push a straight pin through the exact center of the straw at the point of the V with the pin point down. The pin point can now be balanced on any small flat surface such as a pill bottle. A crude drawing of this apparatus is shown below.
Singing Tubes
Obtain an aluminum dryer vent pipe approximately 3 feet long and 4 inches in diameter. Also obtain a 4" x 16" piece of brass, copper, or bronze screen wire. (Heavier guage wire mesh is better). Fold the wire screen lengthwise so that you have a 4" x 4" piece of mesh four squares thick. Slightly fold up each corner of the piece of wire mesh so that it will stay in the tube. Place the mesh 1/5th of the way up the tube. Heat the mesh (from the side closest to the end of the tube) with a propane torch, using a circular motion, until any portion of it just glows red. You may need to wear a glove in case the tube gets hot during the heating process. Do not continue to heat any red portion of the mesh since it will burn up if heated to redness for any length of time. Remove the torch from the end of the tube and place the tube vertically with the mesh closest to the bottom of the tube. The tube should howl very loudly. If it doesn't howl, heat the mesh again and repeat. Using different lengths of aluminum vent tube will create different sounds. Always place the mesh 1/5th of the way up the tube. Some wire mesh has a laquer coating which will smoke when heated. If your wire mesh is coated you need to burn off this coating first using your propane torch and a pliers to hold the wire. (Do this outside!).