Law of Conservation of Energy Explained Simply
Energy can't appear out of nowhere, and it can't simply disappear - it just keeps changing form or gets passed from one place to another. This is called the Law of Conservation of Energy (also known as the First Law of Thermodynamics).
When wood burns, the chemical energy stored inside it doesn't disappear - it's completely converted into heat and light. In the end, there's exactly as much energy as before, just in a different form.
đź’¬ Mia asks Grandpa Theo
If a campfire eventually goes out, is all the energy just gone?
No, it never really disappears! While the fire burns, the chemical energy in the wood gets converted into heat that warms you up, and into light that you see.
But the next morning everything is cold and dark - so where did the energy go?
It's still there, just spread out very far! The heat has flowed into the air and the ground around it, until you can't feel it anymore. In total, there's exactly as much energy left as before - it's just no longer bundled up in one place.
Does that apply to other things too, not just fire?
Always! On a swing, your potential energy at the top turns into kinetic energy at the bottom - and back again. A battery converts chemical energy into electrical energy. But nothing is ever created or destroyed in the process - energy is only ever passed on or transformed.
This exact principle also explains why a falling object keeps speeding up: its potential energy gets converted into kinetic energy as it falls - nothing is lost along the way.
The unit of energy, the joule, is named after the British physicist James Prescott Joule, who showed in the 19th century that heat is a form of energy - one of the key discoveries on the way to the law of conservation of energy. That's also exactly why a perpetual motion machine (a machine that runs forever without any energy input) is impossible: it would break this law of nature.