Conservation of Energy

Have you ever swung so high on a swing that you feel a little tummy-tickle at the very top. For just a moment, you pause, full of waiting energy. Then, whoosh. You zoom back down with lots of moving energy. Or have you ever rolled a toy car down a ramp. It starts slow, then zips faster and faster. I am the secret reason for that. I am also the reason a bouncing ball can never bounce higher than where you first dropped it from. I make sure it doesn't get extra bounce from nowhere. I'm a special rule that nothing in the whole universe can break. My name is the Conservation of Energy.

For a very long time, I was a secret that people couldn't quite figure out. They saw amazing things, like big steam engines that puffed and chugged, pushing heavy trains along tracks. They knew that the heat from the engine's fire was making the train move, but they didn't understand how. Then, in the 1840s, some very curious people started to look for clues. A doctor named Julius Robert von Mayer was one of the first. Around the year 1842, he realized that the heat people felt and the work something did were just different forms of the same thing. Another smart scientist, James Prescott Joule, wanted to prove it. Throughout the 1840s, he did many careful experiments. His most famous one involved stirring water with little paddles. He showed that the work of stirring the water always created a certain amount of heat. He proved you could turn one kind of energy into another. Finally, a man named Hermann von Helmholtz gathered all these clues together. In the year 1847, he wrote it all down and shared my big secret with everyone. He explained that energy can change from one type to another, like from motion to heat, but it is never, ever lost. It can't be created or destroyed.

Once people knew my secret, they started seeing me everywhere. I'm there when you switch on a flashlight. The energy stored inside the battery, which is called chemical energy, changes into light energy so you can see in the dark. I'm even in the yummy apple you eat for a snack. The energy inside the apple turns into energy for your body, helping you run super fast and play all day long. Because people understand my rule, they are inventing incredible new things. They build giant windmills that use my whooshing wind energy to make electricity. They use shiny solar panels to turn the sun's light energy into power for our homes and schools. I am the rule that helps us power our world and dream up a brighter, cleaner future for everyone.