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if i doing experiment on spring-mass system in vaccum,if i pull the to some extent (within elastic limit of spring) & let it go,will the system oscillate indefinitely? (neglect contact frictions at support of wall,spring-mass connections),if not tell the reason? hint :there is no posiibility to loss of sound because there is no medium(vaccum) is there any friction between atoms/molecules of spring during continuous extension & contraction of spring, if it so tell the answer in atomic perspective..please help me

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1 Answer 1

No it won't vibrate indefinitely because energy is dissipated in the flexing of the metal spring.

Ideally when you bend the spring the atoms in the metal would move apart slightly and then return to their original position when you released the spring so no energy would be lost. In practice metals contains various defects like grain boundaries, and when you bend a metal you get motion of atoms at these defects. This motion dissipates energy as heat.

The more perfect the metal crystal structure the lower will be the energy dissipation, so a spring made from a single crystal of metal would dissipate less energy than a normal metal spring. However even a perfect crystal would dissipate some energy and therefore stop vibrating eventually.

This paper from Phys Rev B examines the mechanisms of intrinsic energy loss.

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thanks....as you say practically metals contain voids, defects (i.e vacant of atom),when i pull these type of metal spring it took away some amount of energy to bring the atom to fill the void,and applied energy looking forward to create single crystal, once attain single crstal state,remaining energy should be conservative right, why should not the system oscillate indefinetely with use of this remaining energy? –  sathishkumar Sep 11 '12 at 8:13
    
Even with a perfect crystal there is still some dissipation. See the paper I mentioned for examples. –  John Rennie Sep 11 '12 at 8:21
    
You may also look up structural damping. It turns out the damping coefficient varies with frequency of vibration making explicit solutions difficult. –  ja72 Sep 11 '12 at 17:03
    
You can estimate damping from test results with the log decrement method. en.wikipedia.org/wiki/Logarithmic_decrement –  ja72 Sep 11 '12 at 17:05
    
how the perfect single crystal spring dissipate energy in vaccum? in case of no contact friction –  sathishkumar Sep 12 '12 at 6:01

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