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Q & A: what happens to energy stored in spring

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Most recent answer: 09/13/2013
Q:
Compressing a spring stores elastic potential energy because of the work needed to compress it. If you tie a string around the compressed spring to keep in compressed, then submerge it in acid so the metal gets dissolved, what happens to that stored energy?
- Pierce Hadley (age 17)
Normal, IL, USA
A:

Great question! As the metal dissolves, that little bit of extra energy in the bonds between the atoms has to go somewhere.  Each atom is likely to come off the metal with just a tiny bit more bounce. The energy goes into heating up the solution slightly.

Let's say you've stored about 10 Joules of energy in the spring compression (about 100 N of force, about 0.1 meter, for example, a pretty big spring). Then that energy gets added to the thermal energy of say 1 liter of water. It's got a heat capacity of around 4000 J/°C, so you'd heat it up an extra 1/400 °C.  It's not a huge effect but it should be measurable, with great care.

Mike W.


(published on 09/13/2013)

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