# MORE PHYSICS DEMOS

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Here are some physics demonstrations that you might like to add to your "bag of tricks". If you wish to print out a hard copy of these demos, save it as a "text" file and then import it into your favorite word processor for formatting and printing.

If you have any of your own that you would like to contribute, I'll be happy to give you credit and add yours to this list.

Herb Gottlieb from New York City

(where political demonstrations out number physics demonstrations)

[posted with permission]

ADIABATIC HEATING. A considerable temperature increase occurs when a rubber band is stretched. Hold a thick rubber band against your upper lip and extend it quickly. Your lip can sense the increase in temperature. Allow the rubber band to contract rapidly and note that it suddenly becomes colder.

AIR GLUE. To demonstrate Bernoulli's principle, cut a circular piece of cardboard slightly larger than the end of a thread spool. Push a straight pin all the way into the center of the cardboard. hold the spool so its hole is vertical. Press the cardboard against the bottom of the spool with the free end of the pin inside the bottom of the spool hole. Blow into the top of the spool hole. The air acts like glue and the cardboard clings tightly to the spool as long as there is air motion through the spool.

AIR PRESSURE SUCKER. Is so-called suction a push or a pull? Arrange a flask fitted with a two hole stopper and a glass tube extending well down into the flask which is completely filled with water. Challenge a good-natured student to "suck" water up the glass tube while the instructor holds a finger over the other hole of the stopper. When the student fails to get any water out of the flask, instructor might remark, "Jim is not as big a sucker as we thought." After appropriate comments and removing the finger from the stopper hole, the instructor asks the boy to try again. Suddenly the sucker succeeds. When the class becomes orderly again, explain how air pressure provides the necessary push.

AIR PUCK. Cut a six inch circle of plywood or press board. Cement a small cork at its center, Drill a very fine hole through the disc and cork. Inflate a balloon and fasten its mouth over the cork. Place the apparatus on a smooth surface to see almost frictionless motion on cushion of air.

ANTI GRAVITY. Select two test tubes so that one barely fits inside the other. Partly fill the larger with water and float the smaller one on the water. Quickly invert the tubes. As water leaks out, the smaller tube will rise, apparently defying gravity.

BALL IN FUNNEL. Blow or suck on the small end of a funnel containing a ping pong ball. The ball will not fall out even though the funnel is inverted, so long as air is moving between the ball and the funnel wall.

BALLOON ELECTROSCOPE. Light rubber balloons suspended from long silk strings act as demonstration electroscope. Charge the balloons by rubbing them with woolen cloth or fur. When charged, balloons can be made to stick to flat surfaces such as walls or ceilings.

BERNOULLI BALANCING ACT. Bernoulli's principle can be shown by balancing an inflated balloon or beach ball on a jet of air from the output end of a vacuum cleaner. The balloon will hover near the ceiling and will not fall off although tipped at a considerable angle. A ping pong ball balanced on a fine jet of water will illustrate the same.

BIG TORQUE. Hold the end of a broom handle in one hand and extend your arm and the broom handle horizontally in front of you. Tie a string around a book and hang the book under the stick a few centimeters from your hand. Try to keep the stick horizontal while someone slides the book toward the end of the stick. Although the weight of the stick and book do not change, the torque increases. Lever arm has real meaning here.

BLACK BOX CONTENTS. Into a small box, place small objects and seal box closed. Students can examine box, blindfolded, and tell you: (a) How many pieces are in the box. (b) the shape of the pieces. (c) How heavy the pieces are (density). (d) How big the pieces are. (e) The color of the pieces. By doing this the student has reason to believe that the scientists may know something about the atom even though it has never been seen; as he has not seen the objects in the box.

BOILING WITH ICE. Fill a flask two-thirds full of water and bring it to a boil. Cork the flask and invert it taking care that the hot water does not spill out. Place an ice cube on bottom of flask. As the ice melts, the water begin to boil again. If the flask is corked with a one-hole stopper with a glass tube extended almost to the bottom of the flask, boiling can be effected by reducing the pressure of the entrapped air. You can also run cold water over the flask. Have the student feel the flask temperature as the ice boils the water. of boiling water.

CHAIN REACTION. Arrange wood matches closely on a soft board by means of straight pins placed through them at their midpoint. Hold the board upright and ignite the bottom match. The others will follow in turn to demonstrate a chain reaction.

CHIEF SOHCAHTOH. Sometimes it helps to point out that the sine of an acute angle in a right triangle is the side opposite over the hypotenuse; O/H, oh!. The cosine is "ah". A well known trick is to recall the name of the legendary American Indian physicist, "Chief Soh- cah-toa". (Sine is opposite over hypotenuse; cosine is adjacent over hypotenuse; and tangent is opposite over adjacent.

COLOR ABSORPTION. Using colored pencils, draw a bird in a blue cage. Let the bird out of the cage by covering the drawing with a red filter. Try other color combinations to show the effects of color absorption by filters.

COLORED ROACHES. Many organic substances, dead or alive, show interesting characteristics under black light. Cockroaches are multicolored under ultra-violet light.

CONDENSATION OF WATER VAPOR. A simple cloud chamber can be made from a gallon jug fitted with a one-hole stopper with a short piece of glass tubing. Blow into the jug through the glass tubing to increase pressure. Put finger over end of tube and pull stopper, suddenly reducing the pressure. No cloud is formed. If some smoke is introduced into the jug it provides nuclei about which water vapor condenses. Repeat the performance and watch the clouds form in the jug.

COTTRELL PRECIPITATOR. Attach one lead from a spark coil to foil surrounding a glass tube of about one-inch diameter. Extend a wire from the other terminal of the spark coil through the tube, insulated from the foil. Place a small amount of hydrochloric acid in one flask and some ammonium hydroxide in a second flask. With glass tubing connect the flasks and large glass tubing in train. Blow air into the first flask causing ammonium chloride to be forced into the Cottrell precipitator. Activate spark coil and see 'smoke' consumed. It works near instantly on cigarette smoke.

SHADOW REFRACTION. Place an object on the bottom of a metal pan so that its shadow may be measured. Fill the pan with water and remeasure shadow. Refraction is evident if pan, object, and light source are kept stationary.

CRUSHED CAN. The force of normal external air pressure is sufficient to collapse a rectangular varnish can. In a clean can place a few tablespoons of water and bring it to a boil to expel the air with the water vapor. Close the cap tightly as soon as water boils vigorously. Cool the can by dashing cold water on it. ... two comments: You don't need to run cold water over the can. Be sure to stopper it very soon after you remove the source of heat. If you don't, the reverse effect happens.

DENSITY OF ICE. Some properties of water make interesting conversation pieces. Demonstrate that ice is lighter than water by placing large icicle in milk bottle (ice cubes may be used). Add cold water to fill jar while holding ice under the water. Let ice float and observe how much water overflows as the ice melts.

DIMPLES AND PIMPLES. Heat a spot on a cold light bulb with a blow torch and a dimple will form in the glass. Light the bulb and again heat a spot until a pimple forms.

DRY WATER. Let the student explain why one can pick a coin from the bottom of a beaker of water which has been dusted with lycopodium powder and not wet a finger.

EFFECT OF GAS DENSITY ON SOUND. Fill several balloons with different gases such as air, carbon dioxide, natural gas, helium, and propane to about the same pressure. Fix a whistle to be blown to a short piece of glass tubing. Note the pitch as gas from the different balloons blows the whistle.

ELEMENTARY BATTERY. Show emf produced between solutions of different concentrations by using two copper discs attached to insulated wire and suspended in a dilute copper sulfate solution, then drop a few crystals of copper sulfate in to make the bottom layer more concentrated. Connect the electrodes to a sensitive milliammeter or galvanometer.

ENERGY CONSERVATION. Suspend a bowling ball with a strong cord from the ceiling, Draw the ball back against your nose, with your head against the wall. Release it and stand nonchalantly awaiting its return. It cannot rise to greater than height from which it started. You are save if you do not move or push the ball during its release.

FISSION BUBBLE. Activation of nucleus to fission may be demonstrated by catching a soap bubble between two wire rings with handles. When caught, puncture the top and bottom areas leaving a cylinder between the rings. Carefully pull the rings apart, noticing the shape of the film, until it breaks in two films over each circle.

FLAME DISCHARGE. Ionization in a flame can be shown by holding a lighted match near a charged electroscope. Charged pith balls or balloons lose their charge rapidly when a flame is brought near.

GAMES Games can make both learning and instruction a pleasure. Build puzzle of jumbled letters for other students to solve. An example:

• CTVREO-- has magnitude and direction
• DSEPE -- magnitude portion of velocity
• OHNTPO-- elementary light wave

GROWING SILVER CRYSTALS. Place a copper penny on the glass slide of a micro-projector. Put silver nitrate solution around copper and watch silver crystals form on screen. Note many peculiar characteristics they exhibit.

GYRO ASSEMBLY. Weld bicycle axle nuts in end of iron pipes. Screw the pipes on wheel axle for handles. This makes an excellent gyroscope; better when the rim is weighted by winding it with iron wire.

GYRO BAT CIRCLES. Turn around by swinging baseball bat in circles over head. Reversal of swing reverses motion of body. (Standing on rotating platform.)

GYRO HOME RUN SWING. Show action and reaction by standing on rotating platform and swinging a baseball bat vigorously at a pitched ball. .... This should be amusing- Do it outside, of course.

GYRO MOMENTS. Again on the rotating platform, pirouette. Hold heavy weights at arm's length, have someone rotate you slowly. Bring weights close to body. Explain the marked increase in speed.

GYRO PLATFORM. Construct a rotating platform from an automobile front-wheel and spindle. Rigidness, coupled with small friction and small play in the bearings is amazing. This is useful to demonstrate rotational inertia and maneuvering in space.

GYRO PRECESSION. Holding gyro axis horizontal, Stand on a rotating platform holding a spinning gyro wheel with its axis horizontal. Observe what happens when the axis is rotated to a perpendicular position to the right? to the left?

HAIR RADIO TRANSMITTER. Combing the hair near the aerial of a radio produces static.

HEAT TREATMENT. The effect of heat treatment and tempering of metals can be demonstrated by heating bobby pins to redness in a Bunsen flame. Dip one heated pin in cold water to chill. Allow the other pin to cool slowly. Compare these pins with one that has not been heated by bending each one.

HOLY WATER. Can molecules of water have spaces between them. Pour water into long test tube or graduate until it is three-fourths full. Then completely fill it to capacity with alcohol. Place your palm over the top of the container and invert it. Be careful that no liquid is lost as the water and alcohol mix. Observe that the container is no longer full. (Evidently some alcohol has disappeared in water molecule holes.)

HOT DOG WHISTLE. Tune two metal dog whistles to unison or absence of beats. Heat one whistle with flame. Beats reappear as pitch of heated whistle rises. (please don't burn your lips!)

HOT ROD BALANCE. Drill a brass rod for a screw in one end. Insert screw about half way. Balance rod at its center on a pivot. Throw off balance by moving small screw on one end. Heat on end of rod and it will come to balance again.

HYDROSTATIC SCALE. Weigh yourself by hydrostatic pressure. Use a hot water bottle with a stopper fitted with about two meters of rubber and glass tubing. Fill the bottle with water and connect the tubing so that it extends vertically. Lay the bottle on the floor and cover most of it with a small board of known area. Stand on the board and measure the increased height of the water in the tube. Your weight is equal to the area of the board times the water pressure increase. Calculate the water pressure by multiplying the density of water ( 1 gram per cubic centimeter) by the difference in the water level height when you stand on the scale.

IMPULSE AND INERTIA MAGIC. Done with a lot of flourish, this brings down the house! The mechanics of friction, forces and inertia involved make interesting conversation. Set a glass two-thirds full of water about three inches from the edge of a table. On the glass place a pie tin. On the pie tin and directly over the glass place a spool on end. Place an egg (fresh if you are confident) on the spool. With one foot on the bristles of a springy broom, pull back the handle and aim at the pie tin. The spool rolls on the table, the pie tin scoots to the floor, the glass and the water remain unmoved on the table with the egg unharmed in the water.

LENZ'S LAW. Lenz's Law may be demonstrated with any toy wheel of nonmagnetic material and low friction attached to a convenient holder. Wheel should have spokes for clearest understanding. Spin wheel in air then between poles of a reasonably strong horseshoe magnet. Spokes cut lines of force, induced current field opposes motion.

LOCATING THE CENTER OF GRAVITY. Start with your hands outstretched and palms facing each other about a meter apart. Rest a horizontal stick or metal pipe on the index fingers of each hand. With your eyes blindfolded, slowly move your hands together until the palms meet. Regardless of the starting position of your hands, the center of gravity of the stick or pipe will be at the point where your hands come together.

MAGNETIC WAVES. Suspend a bar magnet on a string. Rotate another magnet under it to show transfer of magnetic energy. What changes the direction of the poles? How can the change be effected without human movement.

MASS SPECTROGRAPH. Properties of alpha, beta, and gamma rays may be demonstrated by propping a smooth board of about eight inches by twelve inches on an incline and arranging a bin with a trap gate at the top so that three different sized balls can be released to roll down the board. Place a strong magnet below the board and just to one side of the gate. Note how each falling ball goes into a separate bin because of the amount of deflection. The gamma may be represented by a brass or aluminum ball, he beta would be the smaller of the steel balls.

MATCH DISCHARGE. Rubber bands or strips can be tied together in bundles and charged by stroking with fur or by other means. A lighted match near the repelling strands will cause them to collapse.

MATCH HEAD DIVER. A Cartesian diver can be made with a Coca-Cola bottle full of water and a match head. Keep breaking off the match stick until the head barely floats. Thumb pressure on the mouth of the bottle makes these little divers zip up and down in the bottle.

NEON SINE. Swing a large 115 volt neon bulb rapidly to show sine curve in space as alternate deltas glow.

NUT DRO Fix six or seven metal nuts on a string at distances in proportion to 1/2 gt^2 where the time is 1, 2, 3, 4, etc. seconds. Hold string vertical and still and let drop. Note there is no difference in the time intervals as nuts strike the floor.

PAPER KETTLE. Boil water in a paper cup. The paper will not burn until the water has boiled away.

PAPER WEIGHT. Cover a wooden slat with a sheet of newspaper except for a few inches which project beyond the edge of a table. Hit the protruding part of the slat with a sharp downward blow of a hammer. The slat breaks without tearing the paper.

PENCIL POINT BALANCE. To demonstrate center of gravity outside of a body and the criterion for stability, borrow two pocket knives from students. Push blades firmly (but carefully) into a pencil near the sharpened end with the handles beyond the point of the pencil. Balance the pencil point on your finger. Since the system center of gravity falls below the point of balance, the system is stable.

PINHOLE EFFECTS. An interesting conversation piece can be made from an empty 35 mm film can. In the center of one end punch one hole with a sharp needle. About the center of the other end punch three pinholes at the corners of an equilateral triangle about two millimeters apart. Look through the one hole and see the three holes. Look through the other end at the one hole and explain what is seen. Label the box "Drunk-O-Meter" and list the following directions: 1 hole-sober, 2 holes-nipping, 3 holes-dog drunk, 4 holes or no holes at all -dead drunk.

POURING AIR. Submerge a beaker full of water in a large water filled container or fish tank. Invert the beaker so its open end is down. Invert a second beaker and submerge it so that air is trapped inside. Pour air from one beaker into another, pouring up. Note fluid nature of the gas.

POURING CARBON DIOXIDE. Construct a series three 5-cm steps that will fit into a wide mouth jar. Set a lighted candle on each step. Slowly pour carbon dioxide gas from an open container into the jar. Carbon dioxide is heavier than air. As it settles it extinguishes the candles one by one starting with the candle at the lowest level. There are many ways to generate carbon dioxide. Try mixing some vinegar with bicarbonate of soda.

PRECISION IN ADVERTISING. Encourage students to think, speak, and write more precisely. Illustrate by using a meaningless advertising slogan: "The Rolls-mobile is bigger and better: -than- (a) a diddie car (b) a freight car (c) last year's model.

RATE OF HEAT CONDUCTION. Three students each holding a rod of a different substance in a flame, will demonstrate the difference in conductivity of heat by their object from the flame. Use about the same sized rods of iron, aluminum, glass, copper.

REACTION OF THE ROAD. Place plank on rollers (doweling). With string, tie a small cart to one end of the plank and stretch a long rubber band between the cart and the other end of the plank. Add weights to the cart to increase its mass. Burn the string to release the system. The road goes one way, the cart goes another.

RETINAL AFTER EFFECTS. Draw a circle in the center of a piece of white paper with colored crayon. Stare at the circle at arms length for a time, then look at a blank wall. A circle of some other color appears on the wall.

ROLLING SPOOL. Select a large spool and wrap several turns of ribbon or twine around it. Place the spool on a table so it can roll when the free end of the ribbon is pulled out from the spool bottom. Observe the direction that the spool rolls when the ribbon is pulled straight up and when it is pulled at other angles closer to the horizontal. With a little practice, the spool can be made to roll in either direction as the ribbon angle is changed. Encourage students to explain the phenomena using terms such as torque, friction, and vector direction of force.

SEEING THE SUN BEFORE SUNRISE. Evidence that one may see the sun while it is still below the horizon can be visualized by looking at a penny at the bottom of a bowl filled with water. Note that the penny cannot be seen over the rim of the bowl unless there is water in the bowl. When the sun first appears in the morning, it is still our of sight below the horizon. Refraction of the sunlight by the atmosphere makes the sun appear higher than it really is.

SELECTIVE IMAGE INVERSION. Print with capital letters the word TITANIUM DIOXIDE. Use a red pencil for the first word and a blue pencil for the second. View both words through the side of a test tube filled with water. Only the red word looks inverted.

SELECTIVE LIGHT SCATTERING. Demonstrate the effect of the sun setting through the dust-laden atmosphere. Add five grams of sodium thiosulfate and 5 mL of concentrated hydrochloric acid to a liter of water in a clear container. Shine a light through the solution and on to a wall or screen. Observe the changes as the colloidal sulfur forms. Scattered blue light can be seen in the solution at a ninety degree angle from the beam. On the screen or wall the spot slowly changes from white to yellow, to red, and then is finally is blacked out completely.

SINGING FLAME VARIATION. Hold a four foot 1-1/2 inch glass tube vertical. Insert in the bottom end at a predetermined resonance point a heavy disc of wire gauze. Heat the wire gauze with burner, then remove flame and hear a phenomenon.

SINGING TUBES. A straight metal blow pipe connected to a gas supply is fixed in an upright position on the demonstration desk and lighted. A thirty to sixty centimeter glass tube of large diameter is lowered over the flame until at a certain position a sound is heard.

SKY HOOK. Cut a four inch piece of wire from a coat hanger. Bend one half inch back on one end so that a leather belt will slip in the hook. Rest the free end of the wire on a finger tip. The belt and wire will hang out in space without apparent support underneath.

SPINNING HAMMER. Mark the center of gravity of a hammer with a spot of paint. Toss the hammer into the air with a spin and note that the spot is the most stationary point of the hammer as it spins.

STANDING WAVES ON A STRING. Wave motion and standing waves can be demonstrated by attaching a vertical string to almost any small electric motor or vibrator. An electric shaver is ideal. Hang weights of varying amounts on the string. As the tension increases, there will be changes in the length of the standing waves.

UNLIMITED WATER SUPPLY. Suspend a water faucet above a sink by a thin wire. Water can be made to flow continuously in a strong stream from the faucet bottom despite the fact that the faucet is not connected to any water pipes. The secret is to use a concealed electric water pump that pushes water up a glass tube into the bottom of the faucet. As the water emerges, it flows over the outside of the glass tube concealing the tube from view. This makes an interesting corridor display.

STEREOSCOPIC VISION. Look through a paper tube at some distant object with the right eye while holding a book over the other eye and close to the tube. It will appear that one is looking through a hole in the book.

STRETCH CHARGE. Stretch a rubber band tightly and rub against an electroscope. Determine the nature of charge produced.

SUSPENDING SOAP BUBBLES. Show that a soap bubble filled with air will float on carbon dioxide. Using a bubble pipe or straw, blow a soap bubble and carefully place it in the center of a jar partially filled with carbon dioxide. Because the carbon dioxide is invisible the bubble appears to be suspended without any support.

SWINGING PENDULUM. Show conservation of energy in a swinging pendulum by noting that it returns to the same level each time. Place an obstruction below the point of rotation so that the arc of swing will be changed. Change the obstruction to a point one half the distance between the lowest and highest levels and again below this point. Explain why the bob loops over the obstruction.

TUBELESS TELEVISION. Prepare a slide with a few simple words such as THAT'S ALL cut in a piece of metal foil. Aim the slide projector so the beam goes out an open door and does not attract attention. In a darkened room, wave a white wand in the plane where the image is focused. Persistence of vision creates a complete image, apparently materializing the words in space.

VARIABLE DENSITY. Moth balls rolled in sodium bicarbonate and put into a cylinder of very dilute hydrochloric acid will rise and fall with regularity.

VARIABLE VOLUME SPONGE. A dry plastic sponge can be measured for volume. Ask how much water you can pick up with it. When wet, it may pick up more than its initial volume. It expands slightly and is mostly a "lot of air holes fastened together."

VISCOSITY REACTIONS. Let a few students with egg beaters beat oils of different viscosity. Those having to beat the heaviest oils will tire first.

VISUALIZED WORK UNITS.Mount a 12 inch length of 2x2 inch wood upright on a base. Mount another one slightly over 9 inches long on the same base. Lifting a one-pound weight from the base to the top of the one foot tower represents one foot-pound of work. Lifting the weight to the top of the 0.76 foot tower represents one joule of work. A feather lifted from the table top on to a piece of paper laying on the table represents an erg of work.A millionth of a millionth of an erg is called an electron-volt.

WATER GLASS SUCKER. Carry a glass brim full of water up a ladder and press it to the ceiling. Ask the "sucker" to push against the bottom of the glass with a long pole while you climb down and put away the ladder and go on about other business. If the ceiling is smooth, the student need not fear that the glass will fall.

WHISTLE BEATS. Prepare two small whistles with a screw in the end so that the length of the air column can be adjusted for different frequencies. Attach the whistles to a Y tube so that they can be blown simultaneously. When the pitch of one is slightly different than the other, a low pitch "beat note" is heard.

WOOD'S METAL. Carve a spoon mold in wood and fill with molten Wood's metal. The spoon will melt in hot water, coffee, or tea. Save the mold to recast the spoon as part of the demonstration.

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