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Suppose a spring with stiffness $k$, is strained by constant forces on each end.

In a frame where the strained spring moves at a constant velocity, what's the total relativistic energy of the moving strained string as $k\to\infty$?

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closed as too localized by Ben Crowell, Brandon Enright, Emilio Pisanty, Waffle's Crazy Peanut, akhmeteli Jun 7 '13 at 4:14

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If this is a homework question, please see the homework policy. Otherwise, can you provide some physical motivation for your question? Why would you expect the energy to be different if the spring is moving or not? –  Emilio Pisanty Mar 5 '13 at 23:03
    
@EmilioPisanty no, it isn't homework question, and there's the kinetic energy of the spring for a start. I'm not sure if there's any other energy to add as $k\to\infty$ –  Larry Harson Mar 6 '13 at 0:11
    
The kinetic energy and the elastic potential energy are independent; the total energy is their sum. You might as well take a frame where the spring is at rest. –  Emilio Pisanty Mar 6 '13 at 0:31
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Thought I dont see the point of k-> infinity –  Prathyush Mar 6 '13 at 1:18
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The point of stackexchange is not to get people to answer someone's question, it's to build up a body of useful answers that everyone can use. I can't understand enough about the motivation for this question to see why it's appropriate for the site, so I'm voting to close it as too localized. –  Ben Crowell Jun 4 '13 at 5:08
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1 Answer 1

The energy is the same no matter what the strain. The stiffness affects the compression of the spring, not the energy. In other words the higher k is the higher the energy density it has in terms of (potential energy)/(strain).

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What about the energy in the stress? –  John McVirgo Jun 4 '13 at 13:50
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