YoYo

This large yoyo shows that a flywheel can store kinetic energy. Start the wheel rotating as if giving a push to a swing, and it can lift you as high as 4 meters above the ground!

The first yoyo is believed to have been invented in ancient Greece. This yoyo, however, is upside down, and you travel upwards in it. The winder acts as a flywheel, a device that is installed in several vehicles, such as cars with a manual gearbox. In a car with an automatic gearbox, the flywheel is replaced by a turbine.

A flywheel is a mechanical invention with the task of storing kinetic energy. This energy can subsequently be used at a later stage. Scientists at Uppsala University have united the flywheel with the electric car to improve battery life, since the flywheel can both store and supply energy. This is more efficient, and reduces wear.

What happens when you yoyo? When it is first thrown, it obtains a high kinetic energy (energy of motion). Since the yoyo has a high rotational inertia, it can store energy in its rotational motion, which enables it to counteract gravity. This is why you can get it to rotate back up into your hand.