The following are Lecture notes from a workshop instructed for teachers of grades 3 - 12 by Dr. Shropshire and offered through the ISU Bureau of Educational Research.
Dr. Steve Shropshire, Department of Physics, Idaho State University, Campus Box 8106, Pocatello, ID 83209, (208) 236-2212
In the descriptions below, grade levels in boldface indicate material directly related to required subjects at that grade level according to state guidelines. Relevant sections from the Silver Burdett & Ginn science series are also listed. SB&G5.7 refers to chapter seven from the fifth grade book from that series. Starred tricks are available as "make&takes".
SIMPLE MACHINES
EQUAL ARM BALANCE
Principle: Lever Grade: 3 SB&G 3.6
Make a long rigid rod by sticking four of five soda straws together. Poke a hole at each end and thread a paperclip through it to support two light styrofoam or paper cups by a loop of thread taped to opposite points on the rims of each cup. Support the rod in the middle with a bent paperclip rigged to contact the rod at two points at least an inch apart to complete the balance. Position the clip so that equal numbers of marbles in the cups are always balanced with the rod horizontal. The balance point should be right between the two cups. Show that if one cup has twice the marbles as the other cup, the distance from the light cup to the balance point is twice the distance from the heavy cup to the balance point, and if one cup has triple the marbles, the distance from the light cup to the balance point is three times the distance from the heavy cup to the balance point, etc.
MOBILES AND MOMENTS
Principle: Lever Grade: 3 SB&G 3.6
This is a good tie in to artsy stuff. Have the students make mobiles with string, straws, sticks and things. Have them start from the bottom up, predicting where they need to tie their threads based on the relative weight of the things they tie to either end. If one side is twice the weight of the other, the distance from that side to the "tie-point" must be half of that to the other end (i.e. the tie point must be one-third of the rod length from the heavy side). In general, if you have two weights to hang from one beam; W1 and W2, and if you call the distance from the W1 end of the beam to the support L1 and the distance from the W2 end to the support L2, then L1 = W2xL/(W1 + W2) and L2 = L - L1.
STRAW ARCHES
Principle: Arch Grade: 3 SB&G 3.6
First make a beam out of a single straw supported between two chairs. Determine its strength by hanging a styrofoam or paper cup by a paperclip in the middle and seeing how many marbles can be put into the cup. Try it again with the cup hung closer to one end. Now tape three straws together to form a triangle. Tape the to the supports so that one straw is in the same position as the beam tried earlier, with the opposite corner of the triangle pointing straight up. Tape one end of a string to the top corner and wrap it once or twice around the bottom "beam" straw, and attach the styrofoam or paper cup to the end of the string. Now see how many marbles it takes to break the "arch". Odds are you won't have enough.
BROOM STICK PULLEY
Principle: Pulley Grade: 3 SB&G 3.6
Have two students face each other, each holding a broom horizontal in front of them with their hands at least 2' apart on the brooms. Tie a slick nylon rope to one broom and wrap it three or four times around both brooms to form a simple pulley. Have a third student pull on the free end of the rope as the other two try to pull the two brooms apart. They will usually fail badly because of the mechanical advantage of the third student.
PENCIL AXLES
Principle: Wheel and axle Grade: 3 SB&G 3.6
Have students push a book flat across their desks to gain an appreciation of the effort required. Have them try it again with four of more pencils or short round wood dowels placed parallel under the book and perpendicular to the direction they want to move it. It will be much easier. Ancient Babylonians, Aztecs, and Egyptians used this to move massive stone blocks to make their temples and pyramids.
COFFEE CANS AND INCLINES
Principle: Inclined plane, Wheel Grade: 3 SB&G 3.6
Fill a large coffee can with sand or dirt and stuff so that your students can barely lift it from the floor to a high table. Place a long smooth ramp (a metal shelf works well for this) from the floor to the same table, and have the students slide the can bottom side down up the ramp so that they feel how much easier it is. Then have them roll the can up the incline for even less effort. You may have to use a rougher incline for the rolling part. Some duct tape on the can or the incline should help.
MOTION AND FORCES
COME BACK CAN
Principle: Scientific inquiry, Energy, Motion Grade: 2, 3, 4, 5 SB&G 2.5, 3.6, 4.6, 5.7
Poke two holes opposite each other near one end of a large coffee can. Poke two more holes near the other end. Make four wire clips out of paperclips and thread one through each hole so that they form hooks on the inside. Wrap duct tape over the holes on the outside of the can to hold the hooks in place. Attach one end of one or more thick rubber bands to one hook, and the other ends to a hook at the other end of the can. Do the same for the other pair of hooks. Attach one or more fishing weights, about a half pound, to the rubber bands in the middle. The weights must not touch the inside of the can when it is lying on its side. Stick plastic lids on both ends, and paint or tape pretty wrapping paper to the can to hide the alterations. As the can is rolled across the floor, the weights stay in place due to their inertia, and the rubber bands wind up, taking energy away from the motion and storing it. The can will come to a stop and return as the rubber bands unwind. Use this as an exercise in scientific enquiry as the student try to guess what is inside the can. Have them come up with experiments to test their ideas.
INERTIAL TOILET PAPER
Principle: Inertia Grade: 5 SB&G 5.7
Clamp a broom to a shelf or something so that it is horizontal at about eye level. Slide two rolls of toilet paper onto the broom, one full roll and the other almost gone. Try to snap off bits of the toilet paper from each roll with one hand without having them move. It will be easy on the big roll because it has more inertia, while you will probably unravel the entire smaller roll because it has a much lower inertia.
INERTIAL BRICKS
Principle: Inertia Grade: 5 SB&G 5.7
Find some cheap string that can be broken with a sharp tug (this is the hard part!). Hang two bricks from some support with this string, and tie more of the same string to the bottom of the bricks and let hang. Pull lightly on the bottom string of one brick and ask students where the tension is the higher. They should be able to tell you that it is highest in the string above the brick. Ask them where the string will break if you tug on it and they will probable choose the upper string. If you tug fast enough, the string will break below the brick. This is because of the inertia of the brick.
INERTIAL PENNEY
Principle: Inertia Grade: 5 SB&G 5.7
Place an index card over the top of a plastic cup with an eraser or other stuff in the bottom of the cup for extra weight. Place a penny or a piece of chalk or something on top of the card right over the middle of the cup. Give the index card a sharp horizontal tap. If the tap is sharp enough and the card is smooth enough, very little force will be applied to the penny because of its inertia, and it will fall down into the cup.
SPINNING EGGS
Principle: Inertia, Momentum Grade: 5 SB&G 5.7
If you quickly stop and release a hard-boiled egg, it will stay stopped. But if you try it with a raw egg, it will start spinning again! This is because the inside of the raw egg is still moving after the outside has been stopped.
BALLOON ROCKET
Principle: action - reaction Grade: 5 SB&G 5.7
Thread a long piece of string through a plastic straw, and tie the string between two chairs. Blow up a balloon (one of the long ones work best) and with the end held shut, tape the balloon to the straw. Let go and you have a balloon rocket! There are TWO good ways to explain this: (1) Action = reaction. Air is pushed out the back, so that the balloon must be pushed forward. (2) Atomistic kinetics. Air molecules strike the inside of the balloon, forcing it outward. With the nozzle open, not as many air molecules strike the "rear" of the balloon from the inside as the front (the extra ones fly out the end!), so that the outward force on the front is greater than the outward force on the rear, and the balloon flies forward.
HOLEY POP CANS IN BUCKETS
Principle: action - reaction Grade: 5 SB&G 5.7
Poke three or four equally spaced holes into the sides of an empty aluminum can close to the bottom with a nail. Make the holes straight so that water will come out in a stream straight out. Tie some string to the pull-tab and submerge the can in water in a bucket. Pull out the can and it should just sit there leaking. Now take the nail and crimp the holes to the side so that the water will shoot out at an angle. If all of the holes are crimped the same way, the can will spin when taken from the water due to action and reaction.
PAPER AIRPLANE PHYSICS
Principle: action - reaction Grade: 5 SB&G 5.7
Have students investigate action and reaction by making paper airplanes with flaps on the wings.
ACTION-REACTION WITH STRAWS AND MARBLES
Principle: action - reaction, Momentum Grade: 5 SB&G 5.7
Cut a "V" notch in one end of each of two soda straws. Tape a marble to the other end of each straw. Place the straws together and parallel to each other pointing in opposite directions on the floor or smooth table top with a rubber band stretched between the two notches. Hold the straws in place with a pencil pressed over them so that when it is lifted the straws are released at the same time. They will be flung in opposite directions with equal force, so that they will have equal momentum, and so should slide the same distance. Try taping two marbles to one straw so that it has about twice the mass of the other. Even though both straws will still have the same momentum, the heavier straw will travel only half the distance of the other because it has twice the mass, and therefore half the initial speed.
BALLOON HOVERCRAFT
Principle: Newton's First Law Grade: 5 SB&G 5.7
Cut a straw-sized hole in the middle of a 10 to 12 cm diameter circular piece of cardboard (formica is much better though). glue or pin a rubber stopper with a straw-sized hole to the cardboard, so that the holes line up. Stick a short (apx. 2") plastic straw (glass is ideal) into the stopper end of the hole so that it sticks out about 1", then attach a balloon to the straw with a twist-tie. Blow the balloon up with a second straw stuck into the cardboard side of the hole. Once the balloon is inflated, remove the second straw and place the "floater" on a smooth surface. While the balloon deflates, the floater is supported on a cushion of air, just like a hovercraft! The floater will (if made carefully) stay in one spot, or if tapped, will move at constant velocity, just as Newton said!
ACTION-REACTION WITH POGS AND BOX TOPS
Principle: action - reaction Grade: 5 SB&G 5.7
Tape a paper clip to the middle of the short side of a 0.5"x4"x8" (or thereabouts) box top so that a wire loop sticks about a half-inch above the top of the box top. Stretch a thick rubber band over the two corners opposite to the clip and tie it with thread to the paper clip so that the rubber band forms a "V" when seen from above. This will serve as a pog-launcher. Place a pog (or some other object, with larger objects needed with bigger box-tops) within the "V" so that it will be launched when the string is cut. Balance the box top on top of two smooth dowels or pencils. When the string is cut, the pog is flung one way and the box top the other.
TWO LITER WATER ROCKET*
Principle: action - reaction Grade: 5 SB&G 5.7
See attached description. Make&take cost: $6.20
PAPER MATCH ROCKETS
Principle: action - reaction Grade: 5 SB&G 5.7
Wrap the upper half of a paper match in one or two layers of aluminum foil. Push a straight pin up under the foil to the match head, and remove the pin, leaving an exhaust channel. Place the match rocket on an incline, a bent paperclip does fine, and heat the foil covered match head with a lighter or another match. Make sure it is not pointed at anyone. As the match head ignites, the chemical reaction produces a lot of hot gasses which escape down the channel at high speed. For every action there is an equal and opposite reaction, so that the match will be flung in the other direction.
HINGED BOARD*
Principle: Center of mass, action-reaction Grade: 5 SB&G 5.7
Attach a hinge between two 8" 1"x"4 pieces of wood. Tie or tape a loop of string or wire 2" from one of the free ends, loose enough to slip a hammer handle under it on the bottom side. Clamp the other free end to a table so that the end with the loop dangles straight down with the hinge forming a 90 degree angle. Ask your students how much weight you need to hang from the loop so that is stays horizontal! As a finale, slip the hammer, handle end first, so that the hammer head is slightly to the table side of the hinge, and the board will stay horizontal. This works because the center of mass of the hammer and the free end of the board are now to the table side of the hinge. Another way of looking at it is that in order to have a hammer close to horizontal while supported a few inches from the end of the handle you have to push down very hard on the very end of the handle. For every action there is an equal and opposite reaction, so that the end of the hammer handle pushes up on your finger just as hard as you push down. This is the same force that pushes the free end of the board up so that it stays horizontal. Make&take cost: $1.80
CENTER OF MASS BODY TRICKS
Principle: Center of mass Grade: 5 SB&G 5.7
Have students stand within a few inches of a wall, facing it without touching. Tell them to stand on their tip-toes. They can't do it without touching the wall, since their center of mass must shift from right over the middle of their feet to right over their toes, and there won't be enough space. You can also have them stand sideways to a wall with their feet about two feet or more apart with one foot touching the wall. Tell them to stand only on the foot farthest from the wall. They won't be able to do this either because they must shift their center of mass from right between their feet to right over the foot farthest from the wall, and they can't move the other leg far enough to do this because the wall is in the way. Another trick demonstrates the difference in position of the center of mass of female and male students. A kneeling student first places her elbows, arms and hands together (as if "praying") with the elbows touching the knees and the forearms along the floor. A chalk box or other object is placed at the student's fingertips. The student then clasps her hands behind her back and is instructed to knock the box over with her nose without her entire body falling over. Females can usually do this, while most males have trouble because the center of mass of males tends to be higher in the body, and harder to keep behind the knees for this trick.
PROJECTILE PENNIES
Principle: Projectile motion, acceleration Grade: 5 SB&G 5.7
Place a penny near the corner of a smooth table. Place a ruler 1" from the penny so that the ruler is parallel to one edge of the table and one end sticks out 2" over the other table edge. Place a second penny on the end of the ruler sticking out over the table. Hold the other end of the ruler fixed by pressing down with one finger while you give the other end of the ruler a sharp tap so that the first penny is flung away to land several feet from the table while the other penny falls straight down. It is important that the second penny is dropped at the same time the first penny is flung. If this is the case, they will both hit the floor at the same time and only one "clink" will be heard. This is because both have the same acceleration (down due to gravity) after they leave the table, even though one is moving forward.
ATWOODS MACHINE
Principle: Newton's second law Grade: 5 SB&G 5.7
Tape two pieces of slick nylon thread or fishing line to the tops of two back-to-back chairs 2' apart so that the lines are parallel and about 1' apart. Attach a 4' length of the same thread or line to two styrofoam cups. Drape the line with the cups over the two fixed lines to form a balance. Place more marbles in one cup than in the other and the heavier cup will accelerate down and the lighter cup will accelerate up. Have your students experiment by measuring the time it takes for one cup to hit the floor. Always have one more marble on one side than on the other, but vary the number of marbles. The net force on the two cups will always be the same (the weight of one marble), but the amount of mass will change. Hopefully your students will conclude that the more mass you have, the lower the acceleration.
COFFEE CAN RACE
Principle: Rotational Inertia Grade: 5 SB&G 5.7
Give students a large coffee can, about a dozen large steel washers, and some duct tape with instructions to tape the washers to the inside of the can or its lid in such a fashion so as to win a "roll the can down a ramp" race. The winner will have more of the mass near the axis of rotation, and so a lower rotational inertia.
RACING SOUP CANS
Principle: Work, Energy, Rotation Grade: 4, 5 SB&G 4.6, 5.7
Chunky Soup vs. Beef Broth, which will win? Choose one can of each, of about the same weight. Start each rolling at the same time, from the same height on an incline. Gravity supplies the same amount of energy to each for the same distance of fall. The beef broth will win every time because most of the fluid will not rotate as fast as the rest of the can. Rotation requires energy. More of the chunky soup's energy goes into rotation as compared to the beef broth, leaving more of the beef broth's energy for transnational motion!
HOPPER POPPER*
Principle: Work and energy Grade: 4 SB&G 4.6
Cut a new racquetball in half, turn each half inside-out, and trim it around the edges with scissors until it pops back when dropped with the curved side up. As it snaps back, it slaps the floor and will jump much higher than it was initially dropped. Talk about conservation of energy and the energy stored in the elastic tension of the popper. Make&take cost: $3.00
CLAY ON A STICK
Principle: Rotational Inertia Grade: 5 SB&G 5.7
Try to balance a yard stick vertically with a big glob (~5 lb) of clay mashed around it near the bottom. It is very difficult. Try it again with the clay near the top. It is much easier. The farther mass is from a pivot point or an axis, the more rotational inertia it has, and the harder it is to get it to rotate. In this case, it is the force of gravity that is trying to do the rotation, and with a large rotational inertia you can easily shift the pivot point back below the clay glob before it has a chance to rotate very much. You can do the same thing with a rod made of soda straws with a marble taped to it.
RULER RACE
Principle: Grade: SB&G
STYROFOAM BALL SWING
Principle: Circular motion, Central forces Grade: 5 SB&G 5.7
Tie a some thread about a large (10" diameter or more) styrofoam ball so that you can swing it about your head in a large circle. Demonstrate that an object must have a force on it towards the center if it is to move in a circle by having a teaching assistant cut the thread by raising a knife up into the plane of the ball and thread. Once the tension in the thread is removed the ball will fly off at a tangent, and not radially outward as someone who believes in the "centrifugal" force might expect.
MARBLE SWING
Principle: Circular motion, Central forces Grade: 5 SB&G 5.7
Thread a 4' length of string through a soda straw. Tape a marble to one end of the string and a styrofoam cup to the other. Place varying numbers of marbles in the cup and swing the free marble in a circle fast enough to keep the cup from falling when not supported. The weight of the cup is the force needed to keep the marble moving in a circle. You have to spin the marble faster with a small circle, and not so fast when the circle is big. If you increase the number of marbles in the cup, you have to swing it faster. The force required to keep an object in a circular path must increase if the speed of the object increases, and the force must decrease if the size of the circle is increased.
PROPERTIES OF MATTER
AIR TAKES UP SPACE
Principle: Air is matter, Volume Grade: 2, 4 SB&G 2.4, 4.5
Make a plug for a glass jar out of clay, and poke a funnel through the top, making sure all is airtight. Quickly pour colored water into the funnel, filling it to the brim. Only a little will flow into the jar, because the air inside cannot be displaced to make room for the water. Poke a small hole through the clay with a needle, and the water will flow freely.
AIR HAS WEIGHT
Principle: Density, Buoyancy Grade: 4, 5 SB&G 4.5, 5.7, 5.5
Inflate two large balloons to about the same size, tape them to opposite ends of a meterstick, and suspend the meterstick by a string tied to the center of the meterstick to form a balloon balance. Adjust the string so that the balloons are balanced. Pop one balloon and the other end of the balance falls, showing that air has weight. Actually what you are showing is that the air in the balloons is slightly more dense than the air around them due to the elastic compression by the latex. The weight of an inflated balloon is always greater than the buoyant force on the balloon from the surrounding air.
AIR HAS WEIGHT II
Principle: Density, Buoyancy, Thermal Expansion Grade: 4, 5 SB&G 4.5, 5.6, 5.7
Make an air balance by suspending one paper sack from each end of a long (~ 1 m) stick that is balanced on a sharp edge. Heat the air in one sack with a candle or a hair dryer, and show that warm air is lighter. It is less dense because it expands with the heat. You can use the same sort of balance to show that room temperature CO2 gas is heavier than regular air.
CO2 IN A BOTTLE
Principle: Phase Changes In Matter Grade: 2, 4, 5 SB&G 2.4, 4.5, 5.6
To illustrate the difference in volume between the solid and gas phase, put a few chips of dry ice into a bottle and seal with a balloon. CO2 is weird in that it goes from the solid phase directly to the gas phase at atmospheric pressure. The balloon will quickly inflate as the CO2 evaporates.
CO2 LADDER*
Principle: Properties of matter, Phase changes Grade: 4, 5 SB&G 4.5, 5.6
Attach two 3' 1"x2" furring strips the long sides of a 3' 1"x12" piece of wood to form a trough. Drill 12 or more equally spaced shallow circular pits with a 1" router bit. Fix household candles cut to about 2" into each pit. Prop the "ladder" at an angle and light the candles. Pour room temperature C02 gas down the ladder to put the candles out. C02 is heavier than air, so that it pours. Fire needs oxygen to burn, and the C02 smothers it. Having the C02 at room temperature shows that it is not the cold that puts out the fire. Make&take cost: $6.40
CANDLES IN A BOTTLE
Principle: Grade: SB&G
POP CAN CRUSH
Principle: Phase Changes, Pressure Grade: 2, 5 SB&G 5.6, 2.4
Boil a small amount of water inside a pop can, then quickly put it topside-down in cool water. The pressure inside the can drops dramatically as the steam inside condenses. Water can't be sucked inside fast enough, and the weight of the atmosphere quickly crushes the can.
EYE HOOK & SCREW EXPANSION*
Principle: Thermal Expansion Grade: 5 SB&G 5.6
Choose an eye hook screw and a round head screw so that the round head screw just fails to pass through the eye hook at room temperature. Screw each into the end of a dowel. You can show that if the eye hook is heated, it will expand so that it will pass over the round head screw. You can also show that the round head screw can pass through the eye hook if it is cooled. Make&take cost: $0.40
EXPANDING TUBE*
Principle: Thermal Expansion Grade: 5 SB&G 5.6
Connect a funnel to one end of a 1 m long copper tube with a plastic tube. Clamp the funnel end of the tube to a table such that the other end sticks over the end of the table. Make an expansion dial by pinning or gluing a thin balsa rod to a short 1/8" dowel. Stick the dowel between the tube and the table as far from the clamp as possible. Alternately pour boiling water and ice water through the pipe. As the rod expands and contracts, the dowel will roll between the table and the tube, and the dial will turn. Make&take cost: $8.50
POP BOTTLE BURPS
Principle: Thermal Expansion Grade: 5 SB&G 5.6
Take a glass pop bottle (if you can find one) and refrigerate it, or cool it with C02. This will work as long as the bottle is above the freezing point of water. Moisten the lip of the bottle with water, and place a dime over the opening. The dime will barely cover the opening to most glass pop bottles, and the water provides a bit of a seal. As the air inside the bottle warms up, it will lift up the dime and burp whenever the pressure inside builds up enough. The only problem is getting your class quite enough so that they can hear the burps.
RUBBER BAND THERMODYNAMICS
Principle: Thermal energy, work Grade: 4 SB&G 4.6
Stretch a large rubber band between two fingers and place it against your upper lip. It will feel distinctively warm. Hold it away from your face in a stretched position as still as possible for at least 30 seconds, release the tension and again place it against your upper lip. It will feel cool this time. In stretching the rubber band, work is being done on it, with part of the work going into heating the band. On relaxing, the rubber band was doing work on your fingers, and drawing on its heat energy to provide this work.
COKE FLOAT
Principle: Grade: SB&G
PINTO BEAN BUOYANCY
Principle: Grade: SB&G
FLOATING CANDLE
Principle: Density, Buoyancy Grade: 5, 4 SB&G 5.7, 5.5, 4.5
Weight the bottom end of a candle with a nail or screw and washers so that the candle just barely floats. As the candle burns, it will continue to barely float, even though part of it burns away. Since the candle is about the same density as water, as part of the candle burns away, the rate at which the force of gravity decreases is about equal to the rate at which the buoyant force (equal to the weight of the displaced fluid) decreases.
BUOYANT BOTTLE
Principle: Density, Buoyancy Grade: 5, 4 SB&G 5.7, 5.5, 4.5
Fill a tall (50 cm is good) tank or jug with water, and fill a small vial with colored water to the point where it just barely sinks to the bottom when sealed. Add salt to the water in the big jug a tablespoon at a time, and note the height at which the vial floats. Salt increases the density of the water, and since the buoyant force equals the weight of the displaced fluid, the buoyant force will increase with the density, so that the bottle will rise.
PASCAL'S DIVER*
Principle: Density, Buoyancy, Pressure Grade: 5, 4 SB&G 5.7, 5.5, 4.5
Fill a 2 liter pop bottle 4/5 or so full of water. Add an eye dropper or a small bottle, or anything (preferably small & clear) that will just barely float with a small bubble of air inside with the bottom side open. Clay works well to weight things down so that the eye dropper or whatever floats bubble side up. Screw the bottle's cap down so that no air escapes. If you squeeze the bottle, the pressure shrinks the size of the bubble, and the "diver" sinks! Reduce the pressure, and it will rise again! With practice, you can have the diver float at any depth with just the right amount of pressure. The buoyant force on an object is equal to the weight of the fluid it displaces. As the bubble shrinks, less water is displaced, so that it's buoyancy is decreased. You control the buoyant force with your grip on the bottle.
Make&take cost: $0.50
BALLOON IN A BOTTLE I
Principle: Thermal expansion Grade: 5 SB&G 5.6
Attach a balloon to a 16 oz or larger bottle, and stick it in a cooler with ice or dry ice. After a while, the balloon will be sucked into the bottle a bit. Heat the bottle with balloon with a hair dryer and slightly inflate the balloon. This is a good demonstration of thermal expansion.
BERNOULLI TRICKS
Principle: Bernoulli Effect, Pressure Grade: 5 SB&G 5.5, 5.7, 5.9
Hook the hose of a Shop-Vac up to the exhaust, so that it blows air instead of sucking. Any vacuum that has such an exhaust will work, as will a hair dryer (with the heat off!), but the bigger the blow, the better. The most spectacular tricks can be performed with a leaf-blower. You may need a nozzle on the end of the hose to get a strong enough air stream. Balance some light balls (ping-pong balls and styrofoam balls are good) on the air stream, and you can do some really neat levitation tricks! Try to see how big a ball you can levitate. In a fluid (like air), pressure is lowest where the fluid is moving the fastest, and the pressure is highest where the fluid is still. The pressure is low within the Shop-Vac air stream, so that balls are actually attracted to the stream. This is called the Bernoulli effect. Airplanes use this to fly. The wings force most of the air over the top, so that the speed of the air is greater over the top of the wing. The resulting pressure difference between the top and bottom of the wing provides the lift. You can even "suck-up" balls if you attach a funnel to the end of your blowing hose, so that it flares out like a horn. The air is moving faster where the funnel is narrow, and that's where the pressure is lowest! Our circulatory and respiration systems in our bodies also rely on this effect, as do many weather phenomena such as tornados and hurricanes.
SODA STRAW ATOMIZER
Principle: Bernoulli Effect, Pressure Grade: 5 SB&G 5.5, 5.7, 5.9
Atomizers are often used to spray perfume, paint, and other stuff. Make one by cutting a soda straw almost in half and bending it at a right angle so that the straw is open on the outside of the angle. Stick one end of the straw into a cup with water and blow into the other end. The pressure will be low within the air stream that passes over the open end of the vertical part of the straw. This low pressure will suck some water up and out of the cup so that it is caught up in the air stream and spewed foreword.
BERNOULLI FLYER
Principle: Bernoulli Effect, Pressure Grade: 5 SB&G 5.5, 5.7, 5.9
VORTEX CANNON*
Principle: Bernoulli Effect, Pressure, weather Grade: 3, 5 SB&G 3.10, 5.5, 5.7, 5.9
Cut a 6" diameter circular hole in the middle of the bottom of a 5 gal. cylindrical food service bucket. Attach a 2'x2' piece of 3/8" neoprene to the top of the bucket with plastic strip ties to form a tight drum head. A sharp blow to the drum forces air rapidly out of the hole in the bottom. The air pressure is very low at the hole when the air first rushes out. This "sucks" more air in towards the hole from the sides right outside the hole. The two air currents meet and spiral together in a spinning air mass shaped like a donut called a vortex. Where air is spinning the pressure is lower, and this sucks more air in, which makes the air move faster, which lowers the pressure even more, which sucks more air in, which makes the air move faster, etc, etc.. This is the same effect responsible for tornados and hurricanes. You can see the vortex by filling the bucket first with "smoke" from CO2 and water. You can blow out a candle at 20 paces with a little practice. Make&take cost: $6.00
GRAPE SODA VORTEX DROP
Principle: Bernoulli Effect, Pressure, weather Grade: 3, 5 SB&G 3.10, 5.5, 5.7, 5.9
Fill a cup with water. Suck up a little grape soda into a straw and pinch it off near the top to trap some of the soda. Place the open end of the straw about one inch above the water in the cup with the straw as vertical as possible, and give a sharp squeeze in the middle of the straw, rapidly expelling some of the soda. A vortex ring as described above forms as the drop hits the water, and it spreads out as it strikes the bottom of the cup. It takes some practice for this one to work.
CURVE BALL
Principle: Bernoulli Effect, Pressure Grade: 5 SB&G 5.5, 5.7, 5.9
Cut a 2"x18" strip lengthwise from a 3' long, 3" diameter mailing tube, or use a different size tube with the strip size scaled up or down appropriately. Bend the sides of the cut portion out so that the cross-section forms a half-circle. Glue rough sandpaper inside the tube, and you have a curve ball thrower similar to the Trak-Ball toy. Place a styrofoam ball in the thrower and toss it with wrist action so that it spins as it flies. As the ball spins and moves through the air at the same time, air moves by one side of the ball faster than the other, because of friction with the spinning ball. The difference in the speed of the air between one side and the other leads to a difference in pressure as well (recall that the pressure is lowest where a fluid is moving the fastest). So as any pitcher can tell you, the ball will curve to the right if it is spinning clockwise, and will curve to the left if it is spinning counter-clockwise. A pitcher can also throw a "slider" by giving a ball a backspin, and throw a "slowball" by giving a ball a forward spin.
SURFACE TENSION
Principle: Surface tension Grade: 5 SB&G 5.5
Poke three holes in the side of a styrofoam cup, close to each other and the bottom of the cup. Fill it with water and three streams of water will shoot out. Run one finger close to the cup through the streams and they will join together even after you remove your finger. The energy of a fluid is lowest when its surface area is minimized.
SOUND
SODA STRAW WAVE MOTION
Principle: Sound, Waves Grade: 6 SB&G 6.9
Take a couple of dozen soda straws and clip a paperclip to each end of every straw. Measure out a little more than 2' of sticky tape, and stick a straw every inch or so with the tape in the middle of each straw. Stick a second identical length of tape over the top of the straws to cover the sticky part of the first tape. Hang the straw strip from a desk or table, pull it taunt, and give one of the straws at the top or the bottom a tap to start a transverse wave. Increasing the tension will increase the speed of the wave, and increasing the density (by adding more paperclips) will decrease the speed of the wave. Although sound is a longitudinal wave, best represented by compression waves in slinkys, the soda straw waves can be used to illustrate many of the properties of sound waves.
SODA STRAW REED WHISTLE
Principle: Sound Grade: 6 SB&G 6.9
Cut two narrow "V's" out of opposite sides of a plastic soda straw at one end, with the "V's" about 5/8" long. Mash the two halves of the cut end flat between your molars to form a double reed like that on an oboe or bassoon. With practice you can blow through the straw with the reed in your mouth to make a buzzing note. You can stick the straw whistle into a polled piece of paper to make a slide (or trombone) whistle, or cut pieces off of the end of the straw with scissors while playing. In any case, the pitch will increase if the whistle is shortened, or decreased if the whistle is lengthened.
DOPPLER NERF BALLS*
Principle: Sound Grade: 6 SB&G 6.9
Attach a 9V battery clip to a 2 - 5 watt buzzer. Stuff this inside a Nerf or tennis ball. Toss it at students, or swing it around your head to illustrate the doppler effect. If something is coming towards you, any sound it makes sounds higher in pitch (frequency) because the sound waves are passing you more frequently. Similarly, something moving away sounds lower in pitch. Make&take cost: $7.00
CANNING JAR VACUUM TRICKS
Principle: Pressure, Sound Grade: 5, 6 SB&G 5.6, 6.9
halfway decent vacuum chambers can be created with canning jars. One of the more interesting demonstrations using these jars is to show that sound needs air to travel. Make a stiff hook for bells or keys out of a coat hanger that will fit into a quart jar (or larger) without rattling around. Put a tablespoon or more of water into the jar, and heat it with the lid slightly less than finger tight. As the water inside boils it turns to steam and forces the air out. Once it is all full of steam, seal the jar tight. Allow to cool. As the water condenses it takes up far less volume, leaving a partial vacuum. To make it better, freeze the jar. Shake it for the students to show that the sound cannot travel without air.
ELECTRICITY AND MAGNETISM
REPELLING STRINGS
Principle: Electric Charge, Static Electricity Grade: 5 SB&G 5.8
Tie about 8 to 10 nylon strings to a rod. Rub the rod with fur or wool, and you remove electrons from the fur and deposit them on the strings. The strings will fly apart since they are all charged, and like charges repel.
CHARGE OF THE LIGHT BALLOONS
Principle: Electric Charge, Static Electricity Grade: 5 SB&G 5.8
Rub two balloons through your hair and you transfer some electrons to them. Suspend them by strings to show that they repel. You can illustrate polarization by showing that a charged balloon will attract an uncharged balloon, but once they touch and transfer charge, they repel. You can deflect a stream of water with a charged balloon because of the polarization of the water molecules. You can also "levitate" light strings and joke about snake charming. Sticking them to walls and ceilings is also fun.
SPIN THE BOARD
Principle: Electric Charge, Static Electricity Grade: 5 SB&G 5.8
Charge up a balloon or a plastic cup, and bring it close (don't touch!) to a 1x4 balanced on a bowl bottom or a lens. You can polarize the wood, and spin it one way, then the other, all without touching.
PICNIC PLATE ELECTROPHORUS
Principle: Electric Charge, Static Electricity Grade: 5 SB&G 5.8
FILM CASE LYDEN JAR
Principle: Electric Charge, Static Electricity Grade: 5 SB&G 5.8
RUB THE TUBE
Principle: Electric Charge, Static Electricity Grade: 5, 6 SB&G 5.8, 6.6, 6.8
Rub a fluorescent tube with wool or fur and it will glow. Electrons are transferred to the glass from the fur, and some electrons dislodge and fly away from the other deposited electrons and excite atoms in the gas inside the tube. As the atoms de-excite, they emit ultraviolet radiation which is absorbed by the phosphor coating on the inside of the tube, which causes the phosphor, and the tube, to glow.
ELECTROSCOPE*
Principle: Electric Charge, Moving electrons Grade: 5 SB&G 5.8
You can construct a simple charge detector with a glass jar, aluminum foil, and some stiff wire. Choose a quart glass jar with straight sides and a plastic lid. Bend a small (~ 2 cm) sideways hook into a 25 cm piece of stiff wire (a stripped piece of coat hanger will work). Stick the unbent end of the wire through a small hole drilled in the plastic lid, and fix the wire in a position so that the hook is in the middle of the jar. A small glob of clay will work just fine for this. Cut the unbent end of the wire so that only a few inches of wire sticks up out of the lid. Once you have the wire where you want it, fix it in place and seal the hole with wax dripped from a candle. Hang two thin (~ 3 to 5 mm) aluminum foil strips from the hook so that they touch. Heat the jar so that it is dry and warm inside, then quickly seal the jar. Top the protruding wire with a ball of crumpled aluminum foil, and you are done! Bring something charged close to the ball, and the aluminum strips repel each other. This is because the wire and foil polarize when something charged is brought near. The opposite charge is attracted to the ball on top, and the like charge is repelled down into the strips, which then repel each other. Remove the charged object, and the strips return to normal. If you touch the charged object to the ball, you transfer charge, and the strips will remain deflected. Knowing the charge of one object, you can determine the charge of other objects with this device. Make&take cost: $2.80
CONDUCTORS?
Principle: Electric Charge, Moving electrons Grade: 5 SB&G 5.8
Make two 1 cm wide, 10 cm long aluminum foil wires by folding strips of foil 3 or 4 times. Tape one end of each to opposite ends of a D battery. Connect the other end of one wire to the side of a flashlight bulb with a clothespin. Tap the bottom of the bulb on the other wire and the bulb will light. You can have your students check various objects to see if they conduct by placing the objects between the loose wire and the flashlight bulb.
FOIL JOULE HEATING
Principle: Electric Charge, Moving electrons Grade: 5 SB&G 5.8
You can have your students take a thin aluminum foil wire and connect it directly across a AA battery. The foil will warm quickly. Moving electrons scatter off of imperfections and impurities, transferring energy to the foil in the form of heat. This is called Joule heating. You can use this to illustrate how a stove or electric heater works.
POCKET CURRENT METER
Principle: Moving electrons, Magnetism Grade: 5 SB&G 5.8
Wrap a long (1 m) aluminum foil wire several times about a compass. Connect the ends of the wire across a battery and the compass will deflect. This is because moving charges create a magnetic field. In fact, all magnetic fields can be traced back to the motion of charges.
A CURRENT IS A MAGNET, A MAGNET IS A CURRENT
Principle: Moving electrons, Magnetism Grade: 5 SB&G 5.8
Poke a hole in the middle of a piece of poster board and run a straight 60 cm large gauge solid wire (not twisted) through the hole. Support the wire and poster board so that the board is horizontal and at the mid point of the wire, with the wire perpendicular to the board. Place several small compasses on the poster board in a circle about the wire. Connect the wire to a 12 V lantern battery with allegator clip wires, and watch the magnets! Moving charges create a magnetic field in the form of circular loops perpendicular to the direction of their motion. For large classes, it might be more convenient to set the wire horizontal pointed towards the class, and trace the magnetic field loops with a dip compass.
ELECTROMAGNET
Principle: Moving electrons, Magnetism Grade: 5 SB&G 5.8
Magnetic fields can be much stronger in materials than they are in air. Wrap an aluminum foil wire several times about a nail, and connect the wire to a D battery, and you have an electromagnet! With the wire looped, the "loops" of magnetic field produced by the moving charges all add up in the center of the wire loop, creating a much stronger field than what a single wire could produce.
THE SIMPLEST MOTOR EVER MADE*
Principle: Electrical energy, Electricity and magnetism Grade: 5, 6 SB&G 5.8, 6.10
See attached. Make&take cost: $2.50
MAKE A MAGNET, BREAK A MAGNET
Principle: Magnetism Grade: 5 SB&G 5.8
Magnetize a hacksaw blade by rubbing it in one direction with a strong permanent magnet using firm slow strokes, with the orientation of the permanent magnet the same at all times. Twenty to thirty strokes should suffice. Use iron or metal filings to show the location of the magnetic poles at the ends of the blade. Also demonstrate that the filings do not stick to the blade in the middle. Break the hacksaw blade in half, and now you have two magnets, each with a pole at each end! You can keep this up until you are bored (or bloody), and you will never get just one pole.
TOTALLY TUBULAR MAGNETS*
Principle: Magnetism Grade: 5 SB&G 5.8
Magnetic fields affect moving charges, but not stationary ones. Similarly, a moving magnet (or a simply a changing magnetic field) can affect a stationary charge. Only relative motion is important (this is what got Einstein going). In other words, a changing magnetic field creates an electric field, and a changing electric field creates a magnetic field. As a general rule, the electric field created by a changing magnetic field will be oriented so that it could cause nearby charges to move in a manner that would create a second magnetic field directed to oppose the change in the original magnetic field. Electric currents created from this effect are called "eddy currents" due the circular motion of the charges. In other words, a moving magnet will create a "virtual magnet" if it moves near a conductor. The virtual magnet will be oriented to slow the moving magnet down. To illustrate this, drop a strong magnet down a copper tube, and show that it takes a lot longer to drop out the end than anything else of similar size and weight. You can also move a strong magnet past a non-magnetic conductor (copper is best) and feel the resistance. Make&take cost: $3.00
SIMPLE BATTERY
Principle: Moving electrons, Chemical reactions Grade: 5, 6 SB&G 5.8, 6.7
Clean or brighten an iron washer and a copper penny. Soak a 1 inch square piece of heavy blotter paper or folded paper towel in vinegar. Press the soaked paper between the washer and the penny to form a simple battery. Measure the current with wires connected to the pocket current meter, with one wire pressed against the washer and the other pressed to the penny. The vinegar induces a chemical reaction between the copper and the iron. Charged "ions" will flow through the vinegar from the copper to the iron. The reaction continues as long as one piece of metal can get rid of its excess electrons through the wires to the other piece of metal to balance the natural flow of charge through the blotter paper.
LIGHT
Color Wheel:
Color Tricks With Cellophane:
Candles & Mirrors:
EARTH SCIENCE
FUNNEL PRESSURE GAUGE*
Principle: Pressure Grade: 3,5 SB&G 3.10, 5.7
Make a U-tube by wiring 70 cm of a 2 m long clear vinyl tube bent to form a 30 cm high "U" (with the last 70 cm of the tube) to a wood stand. Connect the top of the free tube to a funnel, and cover the mouth of the funnel with plastic wrap rubber banded in place. Fill the U-tube half full with colored water, and you have a working pressure gauge. You can use the gauge to illustrate how pressure varies with depth in a fish tank. Make&take cost: $6.00
BALLOON IN A BOTTLE II
Principle: Grade: SB&G
THE WEIGHTLESS STYROFOAM CUP
Principle: Weightlessness Grade: 5 SB&G 5.13
Tape two coins to separate newspaper rubber bands. Poke a hole in the bottom of a styrofoam cup and thread the ends of the rubber bands opposite to the coins through the holes and hold them in place with a paper clip. Adjust the tension so that the coins will barely hang over the outside edge of the cup on opposite sides. Drop the cup and the coins will snap back into the cup. This is because the coins, like anything else, become "weightless" when dropped, but the tension in the rubber bands stays the same. You can show the same thing with a cup with two small holes near the bottom filled with water. As you hold it water will leak out of the cup in two narrow streams. If you drop the cup, the streams will stop.
Funnel Geyser:
Hot & Cold Currents:
Twinkling Stars: