[UmpJM]

Originally Posted by Dave Reed

Well, it's a little slow here on a Friday night, so.....

A couple of pages back, dash_riprock suggested that adding holes to the Reebok bat was silly. MTD. Sr. took him to task, asserting that dash hadn't learned fluid mechanics. dash invited MTD to provide a calculation of drag, but instead got a (wrong) explanation of ball-bat collisions.

Dash was right-- there is little benefit to adding holes to the bat handle. The drag on a cylinder is proportional to the area times the velocity squared. Since the handle moves roughly at 1/3 the speed of the barrel, and the area is perhaps 1/10 that of the barrel, in rough terms the air resistance of the handle is about 1% that of the barrel. Reducing that 1% to perhaps 0.8% is a very small effect.

And the ball-bat collision stuff? MTD starts with the assertion that the collision is elastic. But it isn't. A baseball has a coefficient of restitution of around 0.45 at typical collision velocities, and is limited by rule to 0.565 at 60 mph (less than bunting speed). All the subsequent discussion of conservation of energy and momentum, and sums of velocities is inappropriate for inelastic ball-bat collisions.

Finally, this assertion: "The mass of the bat is much greater that the mass of the ball and it only takes a small increase in a bat's velocity to greatly effect the amount of momentum transfered from the bat to the ball." is way wrong.

If the collision were elastic, a 1 mph increase in bat speed would give a 2 mph increase in ball exit speed. But since the COR is about 1/2, the actual effect is 1 mph in bat speed gives about 1 mph in ball exit speed.

Oddly, I think I actually understood (sorta' ) what Dave Reed said here, and found his argument compelling.

Nicely done.

JM