Bob,
Think about a car even on a hill once you stop pressing the gas the car starts slowing down unless the weight of the car and the grade of the hill allows gravity to continue the acceleration.
In order for anything to accelerate it must have a force acting on it. The car, the force = the engine. The Arrow the force = the limbs of the bow through the bowstring.
Once the force is no longer imparted the acceleration no longer occurs and if we were in a total vacum with no gravity then there would be no deceleration as there would be nothing to act against the force already imparted on the object and stored as stored energy(I believe this is the Kenetic Energy).
When the arrow impacts the KE is used and this use of stored energy is what drives the arrow into the medium to the level of the stored energy - penetration.
The mass(weight) of the object at this point is what determines how effective this transferance of energy is and this determines penitration as a lighter object requires less energy to stop and a heaver object more. The resistence of the target being penetrated determines how much energy is used for this penetration and this determines how far the object penetrates.
I hope I described this accurately and if I didn't please don't hesitate to correct me.
Greg
"Getting close to the game is the joy of Bowhunting for me, the harvest is a bonus."
Live 15 ft Python after eating a small Antelope!
Edited by - amosgreg on 08/14/2002 12:49:38