Quote:
Originally Posted by Mike Schreiber
You can determine your initial velocity using energy (as others were saying).
.5 * k * x^2 = .5 * m * v^2
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In most catapults and kickers, a large portion of the spring energy is not imparted as kinetic energy to the ball. Thus this equation will give a substantially over-optimistic estimate of ball speed if "x" is the total amount the tubing is stretched (including pre-tensioning stretching).
You can increase the available spring energy by adding more strands or tubing and/or pre-tensioning the spring (or surgical tubing) with the launcher (or kicker) against the hard stop in the "fired" position.