Spark plug shatters Car windows?

I have heard/seen small chunks of Porcelain from Spark plugs shatter an entire car window... can someone please explain to me how this small pebble can shatter a window so easily... also, would a chunk of porcelain from a spark plug be able to shatter bullet proof glass?? or other glass things?? or is it only car... show more I have heard/seen small chunks of Porcelain from Spark plugs shatter an entire car window... can someone please explain to me how this small pebble can shatter a window so easily... also, would a chunk of porcelain from a spark plug be able to shatter bullet proof glass?? or other glass things?? or is it only car windows? Thanks.
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