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Is Sound Energy Lost During a Collision in a Vacuum?

Is Sound Energy Lost During a Collision in a Vacuum? - Physics Forum

Is Sound Energy Lost During a Collision in a Vacuum? - Physics Forum. Discuss and ask physics questions, kinematics and other physics problems.


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  #1  
Old 09-04-2008, 04:57 PM
Positron
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Default Is Sound Energy Lost During a Collision in a Vacuum?



Imagine that you have a very elastic collision such that the only
energy lost is due to heat, sound and air resistance.

What will the effect on the amount of energy lost during the collision
be if the collision took place in a vacuum, rather than normal
atmospheric conditions? Of course, if you have a perfect vacuum, the
amount of energy lost due to air resistance would fall away, but what
about the portion of energy lost due to the production of sound in
normal atmospheric conditions?

Since sound waves cannot travel in a vacuum, is energy still lost to
the production of sound? Would the only energy lost in a near perfect
elastic collision taking place in a vacuum be due to heat production
on impact?

Positron
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  #2  
Old 09-04-2008, 05:42 PM
Dirk Van de moortel
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Default Is Sound Energy Lost During a Collision in a Vacuum?

Positron <[Only registered users see links. ].za> wrote in message
[Only registered users see links. ]

When bodies collide elastically they end up vibrating internally.
In air these vibrations are passed to the surrounding air molecules,
generating energy loss, and we hear the vibrations as sound.
In vacuum the bodies' internal vibrations cannot be passed, so
they last a bit longer before they die out and warm up the body.
Of course, these internal vibrations can be called "sound" as
well, but they can only be heard through direct contact between
the body and your ear drum.

Dirk Vdm
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  #3  
Old 09-04-2008, 05:48 PM
Greg Neill
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Default Is Sound Energy Lost During a Collision in a Vacuum?

Positron wrote:

The colliding bodies will "ring" a bit longer with vibrations
induced by the collision, and these will "ring down" or
dissipate through heating of the objects, which heat will
subsequently be radiated away (until equilibrium with the
envioronment is achieved).

With an atmosphere present the virbrations are coupled to the
air and energy leaves as sound. Heat energy can also be
conducted (convected) away by the air.


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  #4  
Old 09-05-2008, 12:31 AM
Darwin123
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Default Is Sound Energy Lost During a Collision in a Vacuum?

On Sep 4, 1:53*pm, PD <[Only registered users see links. ]> wrote:

The energy will eventually dissapate as infrared thermal radiation.
The word "heat" is ambiguous. "Heat" can refer to the kinetic energy
of molecules, which can be interpreted as sound. However, in a vacuum
the heat can't travel away as sound.
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