How does an mechanical impact affect an capacitor?

Question

I am aware that when you short the ends of a charged capacitor or wire it backwards ( pos to neg and neg to pos ) then it "blows up". My question is what occurs when you take a charged capacitor and smash it with a hammer.

Answer 1

For the kinds of capacitors you are talking about, the energy applied by the hammer is greater than the electrical energy stored in the capacitor.  Some small sparks may occur and some smoke may be emitted, but mostly you'll just have a smashed capacitor (that will not work any more).

What happens is that the dielectric (insulator) layers get stretched to the plasitc limit and break, causing a short in the metal layers.  High current flows, heating the metal to the melting point.  As liquid metal flows insulation melts and more current is allowed to flow.  This happens in a very small area but can quickly spread out to a good portion of the capacitor volume.  Melting plastic releases gas, which expands and eventually 'explodes' out of the package.  

The hammer will tend to limit the gas expansion as it provides an instant outlet for the gasses.

When you wire an aluminum electrolytic capacitor backwards it will likely 'blow up', but not necessarily when you short out the leads (of a charged capacitor).

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Answer 2

it gets smashed! what do you expect?

shorting the ends of a cap does not usually cause it to blow up.