What a learner can do afterwards
- States the law of conservation of energy
- Explains why the total energy in a closed system is always the same even though it changes form
- Explains what dissipation means and why it happens in real machines (friction, air resistance)
- Gives an example showing why 'wasted' energy is not lost but transferred to the surroundings
The lesson
Energy is never created and never destroyed. It only moves from one energy store to another, or changes from one form into a different one. Add up every bit of energy before something happens and every bit after, and the total is exactly the same.
When you charge a phone overnight, the electrical energy from the wall doesn't vanish. Most of it transfers into chemical energy stored in the battery. But some of it spreads out as heat into the air around the charger, which is why the charger feels warm. Add the energy stored in the battery to the heat spread into the air, and it matches the electrical energy that went in.
That spreading-out heat is called dissipation. It happens in every real machine because of things like friction and air resistance. The energy isn't gone, it's just spread out into the surroundings, so it becomes too spread out to easily use again.
That's why no real machine turns all of its energy into useful motion or light. Some energy always dissipates as thermal energy to the surroundings, even though the total amount of energy never changes.
Energy is never lost, only transferred or changed into another form, with some always dissipating as heat to the surroundings.
Watch it
Where it sits
Where this leads
Jobs that lean on this skill. Follow one to see everything it is built on.
8 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.