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Old 08-23-2012, 09:32 PM   #61
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Join Date: Oct 2005
Posts: 34,495

Originally Posted by bhupaes View Post
The racquet could be accelerating all the way to impact. But the actual impact lasts only a few milliseconds. As toly pointed out, how much energy could the force have contributed in that time? IMO, negligible for the purposes of this calculation. If someone can prove this to be wrong, I will accept it - I don't have any means other than the above logic to prove my assertion.
The force has already driven the acceleration of the racket, that is why it has reached that velocity! Moreover, the force that acts during collision is huge and when multiplied by the small time is called the impulse. The force is called the impulsive force. See the example of the magnitude of the force below. toly is saying that the force is negligible!!!!

The impact between bat and ball is an extremely violent one, in which the bat imparts a huge force on the ball thereby causing it to change directions and gain speed. Consider a baseball weighing 5.125oz (mass = 0.145kg) which approaches the bat at a speed of 90mph (40.2m/s). After the collision with the bat, with a contact time of 0.7milliseconds (0.0007s)[1,2] the bat has a speed of 110mph (49.1m/s) in the opposite direction. Using Newton's second law we can estimate the average force acting on the ball during the hit:

Plugging in the numbers we find the average force to be Favg=18,436 N, which is equivalent to 4124 lbs of force.
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