Stupid helmet question

J.A.M. wrote:
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.
By definition the percussion is a sharp impact, where time is zero and force
infinite.


Not in real life but as an approximation. The golf ball will
deform (can be seen in high speed films) and it will take a
finite time for the deformation front to move trough the ball.
If not, we would have an infinite stiff ball with an infinite
speed of sound in the ball and no internal loss of energy
and that is unphysical. Percussion
is just a tool used to simplify calculations and not something
you will find in nature.

/Per