One of Sir Isaac Newton’s most enduring gifts to physics is his third law of motion, which states that for every action there is an equal and opposite reaction. This law explains many phenomena, including the lift on a bird’s wings that enables it to fly or the thrust that propels a jet engine forward. You can see Newton’s third law in action with a balloon-powered toy car.
Insert one end of a plastic drinking straw into a round latex balloon. Wrap a rubber band around the neck of the balloon to secure it to the straw.
Make sure that the two are attached by partially inflating the balloon by blowing into the open end of the straw. The balloon should remain snugly attached to the straw.
Place the balloon and straw apparatus on the roof of a small die-cast toy car. The balloon should cover the windshield and hood and the open end of the straw should extend over the back end of the car.
Fasten the balloon and straw to the toy car with clear tape. Wrap the tape around the body of the car to ensure a secure fit.
Inflate the balloon by blowing into the open end of the straw. Pinch the end of the straw to keep the balloon inflated. Place your car on a smooth, flat surface and release the straw to propel your car forward.
The air leaving balloon will propel your toy car forward, since its force is greater than the force of gravity acting on the car, thus proving Newton’s third law.
Make the balloon easier to inflate by stretching it before you attach it to the straw.