SystemicAnomaly

09-13-2009, 02:05 AM

These are excerpts from another (25 page) thread in this forum

... The radar gun should be picking up the speed of the ball at its maximum velocity -- this would happen a short time after it comes off racket, since it takes some finite amount of time for the ball to accelerate up to that max velocity. Someone in another thread claimed that this was a few feet (nearly 1 meter) after contact -- maybe, maybe not...

Sorry, but that is a physical impossibility (unless you stick a burning rocket to the ball). It can *not* accelerate after it has left the contact with the racket strings. Acceleration needs some kind of force operating on the ball. The only force in effect on a ball after it has left the strings is the drag from the wind causing it to slow down...

Nope, you are wrong about this. What you suggest is an impossibility.

Prior to contact, the ball speed is nearly zero (very slow, anyway). The force of the impact accelerates the ball, therefore the ball is initially accelerating as it comes off the racket. Acceleration, by definition, means that the ball is increasing its velocity. The ball cannot achieve it maximum speed instantaneously - it takes a brief, finite amount of time to accelerate up to that speed.

For a ball to go from zero (essentially) up to a faster speed, let's say 120 mph, cannot possibly happen in zero time -- it takes a finite amount of time as I stated above.

... The radar gun should be picking up the speed of the ball at its maximum velocity -- this would happen a short time after it comes off racket, since it takes some finite amount of time for the ball to accelerate up to that max velocity. Someone in another thread claimed that this was a few feet (nearly 1 meter) after contact -- maybe, maybe not...

Sorry, but that is a physical impossibility (unless you stick a burning rocket to the ball). It can *not* accelerate after it has left the contact with the racket strings. Acceleration needs some kind of force operating on the ball. The only force in effect on a ball after it has left the strings is the drag from the wind causing it to slow down...

Nope, you are wrong about this. What you suggest is an impossibility.

Prior to contact, the ball speed is nearly zero (very slow, anyway). The force of the impact accelerates the ball, therefore the ball is initially accelerating as it comes off the racket. Acceleration, by definition, means that the ball is increasing its velocity. The ball cannot achieve it maximum speed instantaneously - it takes a brief, finite amount of time to accelerate up to that speed.

For a ball to go from zero (essentially) up to a faster speed, let's say 120 mph, cannot possibly happen in zero time -- it takes a finite amount of time as I stated above.