Conservation of Energy

Have you ever wondered why a bouncing ball never bounces quite as high as where it started. Or how a rollercoaster, after a slow clack-clack-clack to the top, can suddenly WHOOSH down the track at amazing speeds. That’s all me at work. I’m the reason you eat a big breakfast to get the power to run and play all day. I’m in the bright light from the sun, the booming sound of a drum, and the cozy warmth of a hug. I am a fundamental rule for the entire universe, and my rule is actually quite simple: I can never be made from scratch, and I can never, ever be destroyed. I just change my clothes. One moment, I can be the quiet, waiting power at the very top of a tall slide, full of potential. The next, in the blink of an eye, I can become the zippy, moving power that sends you laughing to the bottom. I change from one form to another, swapping costumes all day long. I might be chemical energy packed into your food, then I become the kinetic energy you use to ride your bike, and even the heat energy that makes you feel warm as you pedal. My real name is a bit of a mouthful, but you can call me the Law of Conservation of Energy.

For thousands of years, people didn't quite understand me. They saw things slow down, like a spinning top wobbling to a stop, and thought that I just vanished into thin air. Poof. Gone forever. But I was still there, just hiding in a new costume. I had secretly changed into heat from the friction between the top and the floor. It took some very clever human detectives to solve my great mystery. They followed clues for many years to figure out my secret identity. One of the first important clues came from a brilliant woman in France named Émilie du Châtelet. Back in the 1740s, she studied the work of other scientists and used her amazing math skills to help figure out the right way to think about moving energy. Her ideas helped get everyone a step closer to the truth, paving the way for the detectives who came after her. The real breakthrough came about a hundred years later, in the 1840s, when a whole team of scientists, working in different countries, finally cracked my code. In 1842, a German doctor named Julius Robert von Mayer was working on a ship and noticed something curious about blood in different climates. This observation led him to realize that the heat in our bodies comes from the food we eat—a perfect example of me changing from chemical energy to thermal energy. Around the same time, an English scientist, James Prescott Joule, was doing some amazing and very careful experiments. Starting in 1843, he built a special machine that used a falling weight to spin paddles in a container of water. He proved, without a doubt, that the energy of motion could turn directly into heat, making the water warmer. He showed you could measure me precisely. Finally, on July 23rd, 1847, a German scientist named Hermann von Helmholtz presented a famous paper that put all the pieces of the puzzle together. He officially announced to the world that I am constant and can only change form. The secret was out.

Just when scientists thought they knew all my secrets, a genius with wild hair named Albert Einstein revealed my biggest one of all. In 1905, he published a groundbreaking idea that showed that even matter—the physical stuff you can touch, like a rock, a chair, or even you—is actually a super-concentrated, sleeping form of me. His famous equation, E=mc², is like a secret recipe that explains how a tiny, tiny bit of matter can unleash a tremendous amount of energy. This discovery changed everything and showed just how deep my secrets went. Today, you see the results of my discovery everywhere. Understanding me is essential for our modern world. I'm why engineers can design powerful cars and gigantic airplanes, knowing exactly how much fuel (my chemical form) they need to get from one place to another. I’m why nutritionists can look at the food on your plate and count the calories, which is just a way of measuring how much of my power it will give your body. I am the reason scientists are building giant solar panels to catch sunlight and towering wind turbines to catch the wind. They aren't making new energy from nothing; they are just cleverly catching me as I change from sunlight and wind into the electricity that powers your video games and lights up your home. I am a promise from the universe: nothing is ever truly lost. It just becomes something new. So next time you flip a light switch, kick a soccer ball, or feel the warm sun on your face, give me a little wave. I'm the shapeshifting power that keeps your world going, forever and always.