Selected activities suggested for grades 3 - 6 at schools hosting a

Forces and Motion Presentation.

In the following descriptions the Grade in bold is the grade in which the Idaho State Board of Education recommends first covering the principle referenced. The numbers following HS (Harcourt Science series, copyright 2000) indicate the grade, unit, chapter and lesson where the relevant principles are discussed. For example, 4F2.1 refers to the Lesson 1 in Chapter 2 of unit F in the 4th grade book.

EQUAL ARM BALANCE

Principle: Lever

Grade: 3

HS 3F3.3, 6F2.1

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 pennies 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 pennies 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 pennies, 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

HS 3F3.3, 4F2.1, 6F2.1

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

HS 3F3.3, 4F2.1

First make a beam out of a single straw supported between two chairs. Determine its strength by hanging a coffee can by a paperclip in the middle and seeing how much water can be put into the can. Try it again with the can 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 coffee can to the end of the string. Now see how much water it takes to break the "arch".

PENCIL AXLES

Principle: Wheel and axle

Grade: 3

HS 1F1.5, 3F3.3, 4F2.2

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

HS 1F1.5, 3F3.3, 6F2.2

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.

PULLEYS

Principle: Pulley

Grade: 3

HS 3F3.3, 4F2.2

A pulley is a machine that either doubles a tension or halves it. When connected as shown at near right, the downward weight of the coin filled cup is balanced by the upward tensions in the two strings. The string is tied to the board then passed down through the pulley and then held from above. If there is little friction in the pulley, the tension in the right half of the string is equal to the tension in the left half. Each portion of the string provides an upward force to the pulley - each equal to half of the weight that the pulley supports. This arrangement allows us to lift the weight with half of the force usually required. However, we would have to pull the string two feet in order to raise the cup one foot. If the arrangement on the far right is used, we still would have to pull with half of the cup's weight, but we would pull down instead of up.

Class 2 Pulley, View 2

If we used two pulleys connected as shown in the near left, we would only need a tension in the string of one-third of the weight of the cup + coins, and we would have the pull the string three feet to raise the cup by one foot. The string is attached to the lower pulley, which is also attached to the cup. The string runs up over the upper pulley, and then down and around the lower pulley, and is then held from above. Three upwards tension forces are applied to the pulley and the attached cup, which are balanced by the one downward force of the cup's weight. If the arrangement in the middle is used, we still would have to pull with one-third of the cup's weight, but we would pull down instead of up. The arrangement on the far left is essentially identical to that in the middle, but a single "double" pulley is used on top instead of two separate pulleys.

Class 3 Pulley, View 3

If we used three pulleys connected as shown in the near right, we would only need a tension in the string of one-fourth of the weight of the cup + coins, and we would have the pull the string four feet to raise the cup by one foot. The string is attached to the board at top, runs down and around the upper pulley in a double pulley that is attached to the cup, then up and over the upper pulley that is attached to the board, down and around the lower pulley, and is then held from above. Four upwards tension forces are applied to the double pulley and the attached cup, which are balanced by the one downward force of the cup's weight. If the two other arrangements are used, we still would have to pull with one-fourth of the cup's weight, but we would pull down.

Replacement Shower Door Roller

A cheap alternative to commercially available pulleys are plastic rollers for sliding screen doors. The type I prefer is shown above at left. To make a double pulley out three of these, bend the 2-1/4" metal tab on all three so that it lies flat, then drill a second hole in each metal tab 3/4" away from the pre-drilled hole, closer to the pulley. Set two of the pulleys back-to-back, rollers down, with the third pulley between them, roller up, with the holes lined up. Bolt them together with two small bolts and nuts. To fashion a hook, bend a length of chain link fencing tie wire (the kind you can bend with your fingers) into a "U" and wrap the ends around the bolts holding the double pulley together so that the bottom of the U hangs down below the double pulley as shown at left. Attach two extra nuts to hold the tie wire in place on the bolts, and bend the metal band on top to center the top pull

SCREW JACK

Principle: Screw, Inclined Plane

Grade: 3

HS 3F3.3, 4F2.3, 6F2.2

Thread two nuts onto a 2" long bolt, 1/4" or 3/8" diameter. Cut a 6" long wood block from a 2"x4". Drill a hole all the way through the middle of the largest side of the block. The diameter of the hole should be larger than the diameter of your bolt by about 1/8". insert the bolt with nuts into the hole and strike the head of the bolt several times with a hammer to "seat" the bottom nut firmly in the wood. Make sure that the bolt can be screwed or unscrewed freely, without touching the wood. You have just made a jack screw, similar to what is found inside many car jacks. A screw or a bolt can be thought of as an inclined plane wrapped around a rod. Push a heavy table so that one of the small sides are against a wall. Have a student or two sit on top of the table (no moving allowed!) and have two other students try to lift the end of the table farthest from the wall up by just one or two inches. They probably will not be able to. Have the students get off of the table and place a screw jack under each of the two table legs that are farthest from the wall. Using the screw jacks and two wrenches, two other students should now have no difficulty in raising the end of the table one or two inches. It will take them a few minutes though. Supervise this closely. Make sure that the screw jacks stay in the middle of the bottoms of the table legs, and that the students keep well away from the table corners in case the table falls off one of the jacks.

WHEEL AND AXLE

Principle: Wheel and axle

Grade: 3

HS 3F3.3, 4F2.2

The wheel and axle is essentially a lever. The axle acts as a fulcrum, and the wheel or wheels attached to this axle can support a load with a force applied somewhere else on the same wheel or on a different wheel. To make the simple wheel and axle shown at right, drill holes in the centers of a large plastic lid from a peanut butter jar and a baby food jar lid. The holes need to be slightly larger
than the diameter of a 4" or 5" long nail, which will serve and the axle. Cut out two rough cardboard circles larger in diameter than the peanut butter lid by about 1/2". Cut out one cardboard circle larger in diameter than the baby food lid by about 1/4". Drill holes through the centers of each of the cardboard circles the same size as the holes in the lids. Cut a square from 1/2" or 5/8" plywood small enough so that it will fit inside of the peanut butter cap. Drill a larger-than-nail-sized hole in the center of the plywood. Thread all of the pieces onto the nail in this order: small cardboard circle, baby food lid - top first, large cardboard circle, peanut butter lid - top first, plywood, then the second large cardboard circle. Clamp all of this together so that they can rotate about the nail freely without wobble, then nail it all together, through both sides. Use nails long enough to sink into the plywood, but short enough so that so pointy ends stick out. Drill a small screw into the side of each lid, and tie a string to each screw. Wind the strings in different directions, and nail the into a small wood block. Clamp the wood block to a ladder or shelf so that the strings dangle freely, and the wheels are vertical. Pull on the string attached to the larger wheel and the string on the small wheel should wind up. Attach a weight to the string on the small wheel and pull it up by pulling down on the string attached to the large wheel. Since the string on the small wheel is closer to the axle (short load arm) than the string on the large wheel (longer lever arm), the weight is easier to lift.

PVC PIPE PULLEY

Principle: Pulley

Grade: 3

HS 3F3.3, 4F2.2

Cut two 3" lengths of 1-1/2" schedule 40 pvc pipe and two 3" lengths of 1-1/4" schedule 40 pvc pipe. Slide the smaller pipes inside the larger pipes and fix each together with two inset screws to form two reinforced pvc bars. Tie one end of a slick nylon rope to a one bar and wrap the other end once around the other bar, as shown in (a) below. Have two husky students try to hold the sticks apart while a third smaller student tries to pull them together by pulling on the free end of the rope. The two holding the bars might win. Wrap the rope around once or twice more (b or c) and repeat. The smaller student will probably pull the rods together now. The rods are acting as pulleys. The two students pulling the rods apart are equivalent to one student pulling on one bar with the other bar clamped to a wall. In case a, the effective force of the smaller student is doubled because there are two tension forces on the right side rod. In case b, the effective force of the smaller student is tripled because there are three tension forces on the left side rod. In case c the effective force is five times greater than the pull of the smaller student.
PVC Pulley

a) b) c)

INERTIAL TOILET PAPER

Principle: Inertia

Grade: 5

HS 1F1.3, 3F3.1, 4F1.2

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

HS 4F1.2

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

HS 1F1.3, 3F3.1, 4F1.2

    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

HS 4F1.1

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.

CD HOVERCRAFT

Principle: Inertia, Newton's First Law

Grade: 5

HS 1F1.1, 3F3.1, 4F1.1, 4F1.2, 6F1.2

Cut out a 1½" x 1½" square piece of index card and slowly poke a hole in the center with a sharp pencil until the pencil lead is no longer visible on the pencil side of the card. Glue a small wooden spool to the card centered over the hole so that you can look through the center of the spool and see the hole in the card. Glue the card and spool to the painted side of a CD with the spool up and the CD on the bottom with the holes in the card and spool centered on the hole in the CD. When the glue is dry, put the nipple of a 6" balloon over the end of the spool, inflate the balloon by blowing through hole in the bottom of the CD. When inflated, twist the balloon several times so that air will not escape until you unwind it. Place the hovercraft on a smooth surface, and allow the balloon to untwist. While the balloon is deflating, the CD is lifted from the surface it was resting on by a thin cushion of air, and the CD can move horizontally with virtually no friction. Give it a push, and the hovercraft will travel in a straight line at constant speed, verifying Newton's first law of motion.

STOMP ROCKET

Principle: Action - Reaction, Newton's 3rd Law, Projectile motion, Acceleration

Grade: 5

HS 3F3.1, 4F1.2, 5F2.2, 6F1.1, 6F1.2

Wrap a piece of notebook paper tightly around a length of 1/2" schedule 40 pvc pipe to form a 8½" long roll. Slide the paper off and use your finger to tighten one end slightly so that it fits snugly inside a 7/8" vinyl cap - the kind you put on the bottom of metal chair legs so they don't scratch the floor. Use your finger to slightly loosen the other end of the paper roll so that it fits easily over the end of the pvc pipe. Tape the roll in at least two places to hold this form, and securely tape on the vinyl tip. This is the rocket. Connect a 4' length of 1/2" schedule 40 pvc pipe to a 4" length of 1/2" schedule 40 pvc pipe with a 1/2" elbow pvc joint. Do not glue, a good twist is tight enough. Stick the other end of the 4" length into a 2 liter plastic pop bottle. If the fit is not tight, use duct tape to hold it in place. This is the launcher. Place the rocket on the launcher and stomp with one foot in the center of the pop bottle, with the rocket pointed up into the air and away from anyone else. Use this to illustrate action and reaction (Newton's third law of motion) and energy transfer. You apply a force to the bottle and the air inside with your stomp. The reaction to this is an equal force on your foot that brings it to a stop. The compressed air applies a force to the rocket, and the rocket applies and equal reaction force to the air. The energy of motion in your stomp is transformed into stored energy in the compressed air, which is in turn transformed into energy of motion of the rocket.

BALLOON ROCKET

Principle: Action - Reaction, Newton's 3rd Law

Grade: 5

HS 3F3.1, 4F1.2, 5F2.2

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, Newton's 3rd Law

Grade: 5

HS 3F3.1, 4F1.2, 5F2.2

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, Newton's 3rd Law

Grade: 5

HS 3F3.1, 4F1.2, 5F2.2

Have students investigate action and reaction by making paper airplanes with flaps on the wings.

ACTION-REACTION WITH STRAWS AND MARBLES

Principle: Action - Reaction, Newton's 3rd Law, Momentum

Grade: 5

HS 3F3.1, 4F1.2, 5F2.2

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.

ACTION-REACTION WITH POGS AND BOX TOPS

Principle: Action - Reaction, Newton's 3rd Law

Grade: 5

HS 3F3.1, 4F1.2, 5F2.2

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.

WOOD SPOOL ENERGY TOY

Principle: Energy, Compound Machines

Grades: 4, 6

HS 3F3.2, 4F1.2, 6F2.2

Tie or otherwise fix a rubber band to the center of a paper clip. Thread the rubber band through the hole in a large wooden spool so that one end of the rubber band sticks out one end of the spool and the paper clip lodges up on the other side of the spool, preventing the rubber band from passing all the way through. Thread a washer over the free end of the rubber band so that any rough edge on the washer faces the spool. Clip off the fuzzy tip of a q-tip and stick it through the free end of the rubber band. Pull the free end of the rubber band tight and tie a knot in it so that the q-tip is held tight against the washer. Adjust the q-tip so that the one fuzzy end is as far out as possible with the cut end held tight against the washer by the rubber band. Add energy to the rubber band by twisting the q-tip around and around. The work you do is stored in the twisted rubber band as elastic potential energy. Set the spool down and watch it go! The energy you stored changes into energy of motion as the rubber band unwinds.

FILM CAN ROCKET

Principle: Energy, Motion, Acceleration

Grades: 4, 5

HS 3F3.1, 3F3.2, 4F1.2, 5F2.2, 6F1.1, 6F1.2, 6F2.2

See the instructions included in the rocket kit.

RUBBER BAND CATAPULT

Principle: Energy, Compound Machines

Grades: 4, 6

HS 3F3.2, 4F1.2, 6F2.2

Cut the top 1/4 off of one two liter plastic pop bottle and the top 1/3 off of another. Cut two 3-inch half-circle holes out of the shorter bottle on opposite sides of each other. With a hole punch, make two opposite holes one-half inch below the top of the shorter bottle - in the middles of the uncut upper edges. Also cut one hole one-half inch below the bottom of one of the half-circle cuts. Place a pencil or wood dowel through the upper holes, and attach a second pencil or dowel to its middle with a rubber band. Thread and tie a rubber band through the lower hole, and attach it to one end of the second pencil. Poke opposing holes near the bottom of a small plastic or paper serving cup, and stick the other end of the second pencil through them to form the throwing cup of the catapult. Fill the taller pop bottle 1/3 full of pinto beans for ballast. Put the shorter pop bottle with the catapult arm into the taller bottle as shown in the figure, and it is ready to fire! By pulling the cup back, you do work (force x distance) and energy is stored in the rubber band. This energy is retrieved when the cup is released. The catapult will then do work on the projectile, and the kinetic energy (energy of motion) of the projectile is increased. Only soft or light projectiles should be used (marshmallows work great!), and students should never be allowed to shoot them at each other. I pulled this out of "Gizmos & Gadgets" by Jill Frankel Hauser. See my Good Book list for a complete reference.

POP BOTTLE WHIRLYGIG

Principle: Energy, Compound Machines

Grades: 4, 6

HS HS 3F3.2, 4F1.2, 6F2.2

Drill a 1/4 inch hole in the bottom of a 20 oz plastic pop bottle, and a second hole in the cap. Tie two rubber bands together and thread them through the bottom hole. Loop one end of the rubber band over a short length of straw so that it prevents the rubber band from snapping up through the hole in the bottom of the bottle as it is stretched. Use a coat hanger or wire hook to pull the rubber band up through the top of the bottle. Thread the rubber band through the hole in the cap, through two washers and loop it around a second straw. Fill the bottle about 1/3 with pinto beans for ballast. Screw the cap onto the bottle, and attach artsy foo-foo thingies to the ends of the top straw. Wind the whirlygig up by spinning the top straw and let it whirl! As you wind, you apply a force over a distance, doing work. This work is stored as potential energy in the rubber band. After you release it, this energy is transferred to kinetic energy as it unwinds. I also pulled this one out of Jill Hauser's book.

WATER BALLOON ON PINS

Principle: Force per unit area

Grade: 5

HS 2F1.1, 5F1.2

Stick a straight pin through a piece of card board so that it sticks straight out the other side as far as possible. Set the cardboard down so that the sharp point of the pin sticks straight up. Try to set a water balloon on top of the pin and, of course, it will pop wetly. Try it with two or three pins close together and you will get the same result. Keep increasing the number or pins and eventually you will have enough to support the water balloon on top of the pins without the pins popping it. The weight of the balloon is spread out over many pins. If you have enough pins, the amount of the balloon's weight on any one pin is very small. For every action there is an equal and opposite reaction so that the force on the balloon from any one pin is also small, too small to puncture the balloon.

CENTER OF MASS BODY TRICKS

Principle: Center of mass

Grade: 5

HS 5F1.2

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

HS 5F2.2, 6F1.1, 6F1.2

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.

COFFEE CAN RACE

Principle: Rotational Inertia

Grade: 5

HS 5F2.1, 6F1.2

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.

HOPPER POPPER

Principle:Work and Energy

Grade: 4

HS 3F3.2, 5F1.3, 5F3.1

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.