The loudness of sound heard when two objects meet together depends on their difference in temperature and state? or the amount of energy transfer?

Amplitude of the sound wave.

I think PG is asking what determines the amplitude of the wave. The first order effect has to be the energy input.

Sound intensity is power/area, therfore, the amount of energy produced per second over the area the sound has traveled when it is heard.

 

For example, if two cars smash together producing 5 watts of sound, and you are 2 meters away from the point of impact, you would hear 5/4pi2^2, or 9.9E-2 W/m^2. This translates into about 100 dB, I believe.

 

I would assume the temperature would have a small effect, but I'm not sure what kind.

I think PG is asking what determines the amplitude of the wave. The first order effect has to be the energy input.

 

This is true, but a higher frequency sound will have more energy than a low frequency one. But this wont appear as louder in our ears.

Sound intensity is power/area

Oh I see.

I may be missing something here, but it seems to me that the amplitude of the sound would be a function of the material of the colliding objects. I.E. two colliding brass bells make a louder sound than two colliding bricks.

True. But that also includes geometry. Bell shapes resonate. Bricks are porous.

There's never a simple answer.