Hand Action at Contact

Eric F said:

I'm not a professor of Physics, but here's what makes sense in my dumb head...

As can be seen in in slo-mo video, the ball compresses and rebounds during the short duration of contact. Likewise, there will also be compression and rebound of the barrel. How much and how fast each of these compress and rebound will be affected by their stiffness and rebound speed. The "trampoline effect" used in bat marketing is describing the barrel of the bat compressing and rebounding. The stiffness (resistance to compression) of the barrel definitely plays a roll in the equation.

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FiveFrameSwing said:

Hi pobguy.

Rumford, Maine …. It’s a small world! Bet you can still remember the aroma of the paper mill.

Your formulation for BBS does not include ‘acceleration’.

Have you collected data in which the 'acceleration' of the barrel was studied going into contact? Have you ruled that out as a factor, or have you simply not studied it?

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FiveFrameSwing said:

A few more questions if you will Pobguy.

I agree that the “master formula” for BBS that you described is “remarkably simple”, but I'd still like to know if it is complete in terms of analyzing the actual system.

I can understand that a bat can be thrown, strike an incoming ball squarely, and result in a home-run. That’s all and good. But let’s say that a batter doesn’t let go of the bat … and let’s say that a batter continues to drive with their top-hand and arm through contact. Why is the ‘mass’ of system being considered only the mass of the ‘bat’ and not the mass of the ‘bat’ + ‘body segment driving through contact’?

Further, why isn’t it proper to evaluate the system from a “force” (F = MxA) perspective? Why isn’t the ‘acceleration’ of the effective mass considered?

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FiveFrameSwing said:

Rumford, Maine …. It’s a small world! Bet you can still remember the aroma of the paper mill.

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pobguy said:

You have asked a very perceptive question. The answer lies in this video: Nathan on Frazier's homer | MLB.com, which is a short clip of my discussion of the Frazier home run at the annual SABR convention in 2012. There are two key points. One is that the bat is not a rigid body. Rather, you should think of the bat as a collection of segments (like slices of salami!) coupled together by very stiff springs. When you whack the bat at the barrel with the ball, the handle only starts to move after a noticeable delay (as seen in the video). By the time the "signal" that the bat has been whacked gets to the handle, the collision is nearly over. And that's the second key point. Namely, the collision is very fast. Nothing at the handle end of the bat could possibly have influenced the collision. So, only a portion of the mass of the bat contributes to the M in your equation, the portion in the vicinity of the collision point. And in particular, the knob and most of the handle do not contribute. Nor does anything attached to the handle (e.g., the hands) contribute. This is not just some "theory"...it is really a fact. Lots of experiments have been done showing that the batter's grip on the bat while the ball and bat are in contact does not influence what happens to the ball.

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pobguy said:

You have asked a very perceptive question. The answer lies in this video: Nathan on Frazier's homer | MLB.com, which is a short clip of my discussion of the Frazier home run at the annual SABR convention in 2012. There are two key points. One is that the bat is not a rigid body. Rather, you should think of the bat as a collection of segments (like slices of salami!) coupled together by very stiff springs. When you whack the bat at the barrel with the ball, the handle only starts to move after a noticeable delay (as seen in the video). By the time the "signal" that the bat has been whacked gets to the handle, the collision is nearly over. And that's the second key point. Namely, the collision is very fast. Nothing at the handle end of the bat could possibly have influenced the collision. So, only a portion of the mass of the bat contributes to the M in your equation, the portion in the vicinity of the collision point. And in particular, the knob and most of the handle do not contribute. Nor does anything attached to the handle (e.g., the hands) contribute. This is not just some "theory"...it is really a fact. Lots of experiments have been done showing that the batter's grip on the bat while the ball and bat are in contact does not influence what happens to the ball.

Click to expand...