Causes of vibrations

• Valkyrie_Lenneth

Valkyrie_Lenneth

I would like to think that: vibrations do not come from thermal energy.

A spring with two masses at each end of that spring do not vibrate due to thermal energy of the air around. That system vibrate because :when the spring is stretched, it creat a force pulling the two masses toward each other, but when the two masses are too close to each other, the spring create a force pushing the two masses apart.
That process goes on and on,which is called vibration.

So , fre vibrations of a system come from the own energy of that system.

I believe that the "energy of that system" to which you refer is the same thing physicists are speaking of when they say "thermal energy" of a system. But even in this illustration, the energy had to come from an outside source. In the case of the wieghts on a spring, it is not heat from the sarrounding air that puts energy into the system, but some external force moving the weights.

The cause of a vibration depends on the system you are examining.
If you are looking at atoms, they vibrate due to thermal energy.
If you look at a larger mechanical system, the vibration is typically due to some other force. For example, a spinning rod or wheel that is not balanced (torque/angular momentum) in an engine/transmission system, or a guitar string that has been pushed.
But the underlying reason is Kinetic Energy.

If you imagine that the electromagnetic force between atoms are springs. Through the life time of these interacting atoms, they will be jostled by a whole host of things. For example infra red energy will interact with the electromagnetic field of the electons in the atom/molecule. Imparting energy to the bounds between the atoms. As energy is not destroyed, one place that the energy manifests is the vibration of these particles. So what you say is correct,vibrations do not come from thermal energy. Molecular vibrations ARE thermal energy.
The interesting thing about these vibrations or heat, is they are highly disorded. So converting this energy to some thing else is very difficult/impossible. Without heating something else.

Duncan

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