Lighter vs Heavier Saftball Bat

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In the question about which is better: a heavy bat or a light one, SDSTAFF Ken
appeals to F=ma. I strenuously object:
1) F= ma is not applicable here
2) Ken applied it incorrectly
3) acceleration magically becomes synonomous with velocity (ack! choke!

Yes, application of a bat to a ball will cause a force on that ball, but a lot of that force goes into deforming the ball. (Imagine the differences in batting a rock, a baseball, a tennis ball, and a water balloon. In that last case, the deformation is spectacular.)The baseball will spring back into shape and this whole complex process is what makes the ball switch directions. This complex process cannot be described with the simple F=ma equation. Ken also seems to think that the force on the *ball* is equal to the mass of the *bat* times the acceleration of the *bat*.

Yeesh! This is why we teach freshman to draw plastic bags around their objects. The force on the *ball* is equal to the mass of the *ball* times the acceleration of the *ball*. In Ken’s interpretation, if the bat has zero acceleration (I think this is called *bunting*), then it applies zero force to the ball, clearly absurd.

And last, acceleration is NOT the same as velocity. Acceleration is the change of velocity with respect to time (dv/dt).

The physics that Ken should have appealed to is the impulse (the change in momentum) where the momentum of the bat (its mass times velocity) can be transfered to the ball.
(think billiards). What’s weird is that all the rest of Ken’s remarks are correct, namely a heavy bat has plenty of momentum but a light bat swung faster has plenty of momentum too. Ken’s quips about Popeye and robots are far superior to anything I could inject.

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