The Pinewood Derby Site
	Pinewood Physics The car is poised at the starting gate. Soon it will roar down the track at a blazing speed. Why is one the clear winner while the other barely makes it to the finish line. The difference is due to physics. Pinewood cars use energy to roll down the track, but unlike the cars your moms and dads drive, the energy does not come from a gasoline engine. It comes from gravity! Energy is something that can not be created or destroyed. It is simply converted from one kind of energy into another kind. For example, the energy in wood is changed to light, heat, and sound (snap, crackle, pop) during a campfire. The energy in a pinewood derby car comes from you! You use your muscles to lift the car to the top of the track. You overcome the pull of earth’s gravity by doing this. The energy you use to pull the car away from the earth does not disappear. It becomes potential energy which is “stored” in the car. More accurately, it becomes potential gravitational energy. More potential energy will result in a faster car. The higher you lift the car above the earth, the more gravitational potential energy it has. So if we can get the car higher on the track , it would have greater potential energy. Actually, you want to raise the car’s center of gravity higher above the track. You do this by raising the weight higher above the track. The center of gravity is the point at the center of the object where it acts as if all its weight were concentrated at that one point. SCIENCE TEST #1 Push an unbreakable object (no dishes or pets) off the edge of a table. When the objects center of gravity passes the edge, the object falls to the floor. If you can balance the object at the end of the table, you will have found the center of gravity. SCIENCE TEST #2 Climb up on a ladder. Have your father climb on the roof. Now both jump at the same time. Who has the most gravitational potential energy? Who do you think will be traveling faster when they hit the ground? Adding more potential energy to your car is like putting a bigger engine in your dad’s car. How else could we get more potential energy? You could do it by adding weight! Which do you think will be the faster car? The sleek one that weighs 2.5 ounces or the wood block that weighs 5 ounces? SCIENCE TEST #3 Find a steep hill and wait for winter. After a good snow storm, you and your father should race down the hill on identical sleds. Who do you think will hit the bottom first? Who do you think will wipe out first? Who do you think will not want to repeat the experiment? When the starting gate is lowered, the potential energy is converted into kinetic energy. This is the energy of action. You would think that two cars with the same potential energy would arrive at the finish line at the same time, but they do not. SCIENCE TEST #4 Hold a heavy object such as a brick or a hammer above your father’s left foot. Now hold a light object such as a feather or a sock fuzz above his right foot. Drop them both. Now which one hits his foot first? Which one would hit first if there were no air? Cars with the same potential energy do not cross the finish at the same time due to friction. Friction is the enemy of kinetic energy. You have friction any time one or more moving parts are in contact with something. Now how many kinds of friction do we have in a Pinewood Derby race? First you have the friction of the air against the car body. This is also called air resistance. If the starting gate does not work fast, you could have the friction of the car against the starting peg. Then you have the friction of the wheels against the axle. There is friction when the wheels hit the car body and when the wheels hit the center strip. The wheels are in contact with the track so there could be friction there also. The friction changes the kinetic energy into heat, and sound. The temperature of the wheels and axles goes up and the car makes a chattering sound as it goes down the track. But, heat and sound don’t make the car go faster. Only the kinetic energy does that. SCIENCE TEST #5 Go to pinewood derby. Stand at the end of the track and close your eyes. Listen to the cars traveling down the track. Do they make noise? Choose the losing car by how much noise it makes. What have we learned so far? There are two main ways to make your car go faster. One is to increase the car’s potential energy. The other is to reduce friction. The ways to increase potential energy are: 1. Raise the center of gravity (weight) higher above the track. 2. Increase the weight. You want to reduce friction: 1. where any two moving parts of the car or track touch each other. 2. where the car is in contact with the air. COPYRIGHT  1996,1997, 1998                          Randy Worcester Material and graphics contained within these pages may not be reproduced without permission. Page updated 3/23/98