Mystery #3Tier 2-3gases / heat
Why does a bike pump grow warm in your hands as you pump hard?
Pump up a bike tyre and after a minute the metal pump feels warm, sometimes almost hot, against your hand. You have not lit anything or plugged it in anywhere. The only thing you have done is push the handle in and out. So where is that heat coming from?
Your guess
What's your best guess for where the pump's warmth comes from?
There's no single magic word to type, have a go in your own words, then reveal the answer to see how close you got.
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