What do you think about this huge yoyo? It’s a big disk with a rope wrapped round it. Tug sharply on the rope and fly into the air. The rope rolls around the disk. If you dangle from above, you are full of adrenaline … and energy: gravitational energy. The higher you are, the more gravitational energy you have.
As the rope unwinds and you come back down, this gravitational energy is converted into motion, or to put it a better way, kinetic energy. Once your feet are back on the ground and you give it another tug, you fly back up again. Then you lose kinetic energy, but you build up gravitational energy again.
As you can see, energy doesn’t disappear. It can, however, be converted from one form to another. This is called the law of the conservation of energy.
One last tip: when your feet touch the ground, bend your knees. That way, you’ll fly up the most!
The law of the conservation of energy with windmills
Windmills work thanks to the wind and the law of the conservation of energy.
The wind makes the windmill’s blades turn. There is a generator in the windmill which converts the movement of the blades into electricity. Or to put it a better way, it converts the kinetic energy into electrical energy.
The law of the conservation of energy with a yoyo
If you hold a small yoyo up in the air it is full of gravitational energy. When you let it unwind, this gravitational energy is converted into kinetic energy. When the cord has fully unwound, it goes back up due to this kinetic energy and the cord winds up again. Then, the kinetic energy is being converted into gravitational energy again. And so it goes on.
Friction with the cord and the air always converts a bit of the energy from the yoyo into heat. That’s why you always need to give your yoyo another little tug.
The law of the conservation of energy when eating
Why do you eat?
When you digest food, energy is released. This is called chemical energy. Your body converts this chemical energy into other forms of energy, such as kinetic energy (when you do sport, write, etc.) and heat (keeping your body temperature at the right level).