Eli5 why living things get hot when they use energy.

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I first thought about friction, but we still warm up when we’re concentrating on something really hard.

In: Biology

Any conversion of energy from one form to another (or indeed any change at all) creates heat. Living things do a *lot* of transforming energy from one form to another, and so they generate a lot of waste heat in the process.

Question: what do you mean warm up when we concentrate real hard?

It’s a byproduct of our cellular metabolism. Our cells are like little engines that use glucose as fuel for energy to do work, not entirely dissimilar to the way a car engine that uses gasoline as fuel gets hot when you drive. Everything that uses energy creates heat.

As for concentrating though, that’s not a thing. Yea, when you’re concentrating hard on something, your brain is using more energy, but no enough that it would raise your body temperature by any amount that you would notice or that would be significant compared to natural fluctuations in body temperature throughout the day.