Stupid helmet question

"J.A.M." wrote in message
...
Nope. Instant acceleration and deccelerations occur, and then the time
tends
to zero and the forces tends to infinite. It's called percussion in
physics.
Classic example are the snooker balls. Also hitting a golf ball. No time
between the club hits the ball and it goes flying.

If you watch a slow motion image you'll find there is in fact a delay and
elastic deformation, small to be sure, occurs in both ball and cue/club.
Trick shots rely on this interaction, for example if you want to jump
the cue ball over another you strike down onto the top surface of the
ball, its the elastic rebound that makes it jump.


By definition the percussion is a sharp impact, where time is zero and
force
infinite.

Thats a simplification, to be true in real life this would require materials
that were completely inelastic. These do not exist.

Keith



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