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Name: Jonathon
Status: other
Grade: other
Location: FL
Country: N/A
Date: 11/2/2005


Question:
If you compressed a spring until you had a measurable amount of energy stored within the spring, then you tied both ends of the spring together (securing the energy within the spring), then immersed the compressed spring into a vat of acid (theoretical acid that would deteriorate the entire spring at the same rate) until the spring was completely dissolved, where does the spring potential energy go?


Replies:
Dear Jonathon,

The energy would go into heating the vat of acid.

When the spring is compressed, the work goes into pushing the molecules in the spring closer together. The force with which they repel each other is then larger then if the metal is not compressed.

So when the spring disintegrates, the molecules separate at a higher speed than they would if the spring were not compressed. The additional kinetic energy of all the molecules would just equal the energy stored in the spring by compressing it. The moving molecules then collide with the molecules of acid and heat them up, The additional heat energy is then just equal to the energy stored by compressing the spring,

Best, Dick Plano, Professor of Physics emeritus, Rutgers University


It goes into extra heat in the final acid solution. The solution with the compressed spring could be a fraction of a degree warmer than the same with no compression. As the acid pries each atom off the solid metal, the stored force can be manifested as a slightly easier or more energetic separation from the solid. After all, the elastic deformation means that each microscopic crystallite in the metal has been stretched to a less-favorable shape, where the electronic bonding between atoms can not have quite as much strength. In this sense, a solid stretched near its limits is slightly less of a solid. It is a slightly less stable substance.

There is a commonly discussed phenomenon in metallurgy called stress-induced corrosion, which is partly related to this, and partly more like chemically-accelerated crack-propagation. I think stress may noticeably accelerate mass-loss in the early to middle stages of dissolution in acid. Spring-grade (hardened, brittle) steels are rarely rust-resistant!

Do not forget that your spring may break before it is all dissolved, and then it is stored energy would suddenly thrash the liquid, ending up as a little heat. Well, you have postulated a closed system with a single inevitable final state, so the energy all ends up the same place, regardless of the exact sequence of the events.

Jim Swenson


In principle, the heat released when a compressed (or expanded) spring is dissolved is greater than the same spring dissolved in acid when it is in equilibrium. However, the energy of compression or stretching is small compared to the heat of reaction of the spring with the acid, so it is barely noticeable.

Vince Calder



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