Understanding the Heat Energy of Springs: Exploring Feynman's Explanation

[Aleoa]

In an ideal reversible case, a spring is a simple perpetual machine ; in order to introduce the slowdown of a spring in a real case and the consequent heat development in the spring, Feynman writes (here par. 4.4):

"Inside a spring or a lever there are crystals which are made up of lots of atoms,
and with great care and delicacy in the arrangement of the parts one can try to
adjust things so that as something rolls on something else, none of the atoms do
any jiggling at all"

I don't understand what Feynman means with this sentence. Can you help me ?

 

[BvU]

If there were no jiggling, there would be no conversion of kinetic energy of the rolling object into random kinetic energy in that object and/or in the something else it is rolling on. In a spring this would not be rolling but e.g. wringing.

 

[Aleoa]

If there were no jiggling, there would be no conversion of kinetic energy of the rolling object into random kinetic energy in that object and/or in the something else it is rolling on. In a spring this would not be rolling but e.g. wringing.

Suppose we stretch and the release a spring with no weight connected. If I've understood correctly, the conversion of kinetic energy is due to the atoms that, instead of stretching and contracting, start to move in random ways . Am i correct ?

ps: since in a spring there is both potential energy and kinect energy, why do we speak only about "conversion of kinetic energy into heat energy " ?

 

[jbriggs444]

ps: since in a spring there is both potential energy and kinect energy, why do we speak only about "conversion of kinetic energy into heat energy " ?

When potential energy is converted to heat in a spring, it is usually first converted to kinetic energy.

I suppose that one could convert potential energy directly to heat if a compressed steel spring rusted away to nothing without breaking first.

 

[Dale]

I suppose that one could convert potential energy directly to heat if a compressed steel spring rusted away to nothing without breaking first.

Interesting thought. I guess anything that would reduce the spring constant while it was extended would also work.

 

[Aleoa]

Suppose we stretch and the release a spring with no weight connected. If I've understood correctly, the conversion of kinetic energy is due to the atoms that, instead of stretching and contracting, start to move in random ways . Am i correct ?

 

[jbriggs444]

The atoms do not stretch and contract. They shift relative to one another. But they do not shift simultaneously and smoothly as a continuous whole. So yes. In addition to the bulk shift of position, there is energy lost into random wiggles.