Question: What is energy?
Answer: You know you're discussing a fundamental topic when you have to find alternatives for words like "stuff". Energy is one of those properties that goes to the core of the universe, and it doesn't get much more fundamental than that. A clue to this question is when you complain you don't have the energy to go to work. Energy is that which enables work.
If you were, say, writing a newspaper column, you'd be expending electro-chemical energy in your brain to formulate words on some topic. This energy is chemical, derived from burning sugars, which come from food, which ultimately is derived from nuclear energy in the sun.
It would also be powering the muscles in your hands to tap the keys. Here we see kinetic energy, which relates to movement and mass.
Your computer uses electrical energy controlled by circuitry to store information and light up the pixel display.
If at the end of all this you're exhausted and nod off, there's the potential that gravitational energy will cause you to slump over. As your forehead bumps the table, kinetic energy is converted into heat and sound, which then dissipates.
Congratulations, you have just contributed to entropy, and the ultimate running down of the universe.
In this case, the energy isn't actually lost, because physics says energy can neither be created nor destroyed. It is, however, in a form that is effectively unavailable. There are no bacteria or algae that feed on bumping objects.
It's easy to confuse magnetism with energy, but in fact it's considered a force. The clue here is that you can't use up a magnet any more than you can use up a wall by pressing against it.
Every facet of our lives uses energy, much of it from finite reserves buried as oil, coal and gas. It is like a giant battery that we are running down at a prodigious rate.
Answer from Rod Taylor, Fuzzy Logic.
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