A plastic bag crumpled on the table to start, no sound, will soon be issued a crackling sound, why?
The sound made by the vibration, sound depends on the intensity of vibration, is the release of energy in the process size, and this energy is obviously to people to do work on it transformation. This difference between plastic bags and table,
Clear plastic bag is very light, as you he will have a relatively large movement (including the shape change, according to the work itself) = force * displacement (W=F * S) this process work should be relatively large, and the table when you knock occurs only very little deformation, when the displacement the power is not reaching zero, natural work rarely. Of course there is the process of transforming to other energy, but the effect is generally not great.
