Picture this... I take an elastic band, similar to one that people use to work out. Much larger than a rubber band.

My friend has lost a bet and I decide that his punishment is for me to put the band around his waist, take a few steps back and release it to give him a painful outcome.

With the band around his waist and me holding it while standing behind him, I take steps backwards, stretching the band as I go. This clearly builds an enormous amount of spring potential energy in the band.

Seconds before I release the band I decide that I am too good of a friend to hurt him this badly, so i walk back towards him, decompressing the band to the point where it still holds to his waist but the tension and fiction aren't small enough to allow it to fall down.

My question; after walking back towards my friend, where does all of the spring potential energy go?

It surely does not become kinetic, or gravitational potential (or I don't believe it does). Did the energy dispersed into invisible molecular forces? Or is work done by my muscle as mechanical/chemical energy?

Comments if you don't understand are appreciated

  • Hint: Where did the spring potential energy come from? – sammy gerbil Mar 23 at 17:48
up vote 1 down vote accepted

after walking back towards my friend, where does all of the spring potential energy go?

Into you. As you walk toward your friend, you’re still pulling away from her: you’re doing negative work, taking energy from the band and putting energy into you.

Where does it go then? That’s the complicated story of muscle biochemistry, etc.

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