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Old 01-25-2019, 01:30 PM
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Baseball physics question

It's a Friday afternoon (here in NY) and I'm not asking a question about the Jewish religion! Seems like those questions always turn up during the Sabbath.

Anyway, here's my question:

You have two batters, one is 100 lbs and one is 200 lbs. They both get the same weight bat up to the same speed when the ball contacts the bat. Same pitch, no air friction, etc. Does the ball go the same distance?

What about if one the lighter batter has freakishly heavy arms and the heavier batter has light arm, so that their arms weigh exactly the same, but their total body weight is still 100 pounds different. Does that affect the ball distance?
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Old 01-25-2019, 01:38 PM
Jonathan Chance Jonathan Chance is offline
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I'm thinking either one would likely hit a strong single to GQ.

Look at it go!
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Old 01-25-2019, 01:41 PM
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Originally Posted by Jonathan Chance View Post
I'm thinking either one would likely hit a strong single to GQ.

Look at it go!
Man, I can't believe I posted that in ATMB. Thanks for moving it!
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Old 01-25-2019, 01:50 PM
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Power is generated by the legs, transferred to the torso then through the arms. Imagine how far you could hit the ball if you stood still and just swung the bat with only your wrists.
It's like cracking a whip.
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Old 01-25-2019, 02:15 PM
Barkis is Willin' Barkis is Willin' is offline
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If I understand the question correctly, you want to know if 2 different guys will hit a ball the same distance if literally the only variable is their weight. They generate the same bat speed, the pitch speed is the same, swing angle is on the same plane, both make contact on exactly the same part of the same bat. Distance is about exit velocity and there are a lot of variables that go into exit velocity. But weight of the guy swinging the bat isn't one. So yeah, they'll hit it the same distance.
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Old 01-25-2019, 02:50 PM
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Originally Posted by Barkis is Willin' View Post
If I understand the question correctly, you want to know if 2 different guys will hit a ball the same distance if literally the only variable is their weight. They generate the same bat speed, the pitch speed is the same, swing angle is on the same plane, both make contact on exactly the same part of the same bat. Distance is about exit velocity and there are a lot of variables that go into exit velocity. But weight of the guy swinging the bat isn't one. So yeah, they'll hit it the same distance.
Yes, that is my question. And I know that, for all practical purposes, bat speed is all that matters. But, this is a physics question, not a baseball question.

I'm not saying you're wrong, but does the momentum of the bat holder matter at all, even theoretically? Or, is the bat (and arms?) effectively decoupled from the body holding it? Would it then not matter if the batter let go of the bat an instant before it struck the ball (so the bat speed is still the same)?
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Old 01-25-2019, 03:30 PM
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https://www.acs.psu.edu/drussell/bats/impulse.htm

The inputs are just weights and speeds of the bat and ball. Essentially, the batter is only interesting in that he or she gets the bat up to speed. For a collision that lasts .7 milliseconds, the bat is essentially unanchored object.
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Old 01-25-2019, 03:48 PM
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That's what I suspected. Thanks for the cite!
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Old 01-25-2019, 03:56 PM
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Speaking abstractly, the bat would be almost like an unanchored object, but the batter is still exerting some nonzero force, and imparting some nonzero work, during the brief duration of the collision, so there would be some slight advantage to the bigger batter.
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Old 01-25-2019, 04:06 PM
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Originally Posted by Chronos View Post
Speaking abstractly, the bat would be almost like an unanchored object, but the batter is still exerting some nonzero force, and imparting some nonzero work, during the brief duration of the collision, so there would be some slight advantage to the bigger batter.
If he is also stronger.
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Old 01-25-2019, 04:19 PM
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If he is also stronger.
Right. Let's hold their strengths equal. All is equal except weight.
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Old 01-25-2019, 09:19 PM
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In my mind, answering this question, I think about the following scenario:

1) A bat is swung to hit a pitch, but the mechanism holding the bat has a relatively loose grip, and, upon contact, the bat is knocked out of the grip.

2) A bat is swung to hit a pitch, and the mechanism holding the bat has a relatively strong grip, and, upon contact, the bat is firmly kept in the control of the mechanism and continues on the swing plane.

In my estimation, the ball should go farther in 2 than in 1. That seems to indicate that, to the extent "power" is involved between our batters, the question is the ability of the batter to power the bat through the interaction with the ball. Weight alone won't do that.
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Old 01-25-2019, 10:05 PM
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I think all other things being the same (skill/power/pitch) the heavier player will hit it slightly further, due to the fact the that the larger mass will resist being pushed backwards by the ball. The difference will be negligible.
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Old 01-25-2019, 10:14 PM
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Quote:
Originally Posted by DSYoungEsq View Post
In my estimation, the ball should go farther in 2 than in 1. That seems to indicate that, to the extent "power" is involved between our batters, the question is the ability of the batter to power the bat through the interaction with the ball. Weight alone won't do that.
I'm not so sure. The notion of powerful athletes having 'soft hands' comes from somewhere. Golf instructors will tell you to just let the club sit in your hands rather than grip it.
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Old 01-25-2019, 11:25 PM
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Originally Posted by MrKnowItAll View Post
I think all other things being the same (skill/power/pitch) the heavier player will hit it slightly further, due to the fact the that the larger mass will resist being pushed backwards by the ball. The difference will be negligible.
Any energy that goes in to making the bat rotate after the collision is energy that doesn't go into making the ball travel. The tighter a grip the batter has, or the heavier his forearms, the less energy is lost to the bat.

But it also depends where the ball hits the bat. If the path of the ball at the point of contact passes through the CG of the bat, then the collision will slow the bat but won't impart any force that causes it to rotate. In that case, the weight or grip of the batter doesn't matter.
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Old 01-26-2019, 12:50 AM
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Originally Posted by Ike Witt View Post
I'm not so sure. The notion of powerful athletes having 'soft hands' comes from somewhere. Golf instructors will tell you to just let the club sit in your hands rather than grip it.
A golf club is substantially different from a baseball bat (for reasons that should be obvious), and trust me, as one who has played golf for over 50 years, you don't just let a club sit in your hands; it would fly out on the downswing, if not on the backswing or the follow through.
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Old 01-26-2019, 05:50 AM
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Quote:
Originally Posted by Telemark View Post
https://www.acs.psu.edu/drussell/bats/impulse.htm

The inputs are just weights and speeds of the bat and ball. Essentially, the batter is only interesting in that he or she gets the bat up to speed. For a collision that lasts .7 milliseconds, the bat is essentially unanchored object.
Quote:
Originally Posted by Chronos View Post
Speaking abstractly, the bat would be almost like an unanchored object, but the batter is still exerting some nonzero force, and imparting some nonzero work, during the brief duration of the collision, so there would be some slight advantage to the bigger batter.
I was amazed when I plugged in the equation but Chronos seems to be right, if the collision lasts .7 milliseconds and Google is right about the speed of sound in wood at > 3000 m/s. The collision lasts long enough for the force from the grip to interact with the collision site.
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Old 01-26-2019, 08:26 AM
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Originally Posted by Ludovic View Post
I was amazed when I plugged in the equation but Chronos seems to be right, if the collision lasts .7 milliseconds and Google is right about the speed of sound in wood at > 3000 m/s. The collision lasts long enough for the force from the grip to interact with the collision site.
Does it last long enough to travel down the bat and arms to make the weight of the body matter? (I could probably do the math, but you seem to have the equations ready to go)
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Old 01-26-2019, 08:37 AM
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It does have enough time to interact with the body as a whole, but I don't know if it would make the weight of the body matter, or just the strength. ETA: only barely since I'm assuming that waves travel through the human body at the same speed as through water, which is slower than wood.

Last edited by Ludovic; 01-26-2019 at 08:39 AM.
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Old 01-26-2019, 12:54 PM
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Alan Nathan is a scientist that studies this stuff. Here's an article he posted about the batter's grip at impact has zero influence on the path of the ball (in summary: the wave generated by impact that travels to the knob of the bat and back to area of impact takes longer than the duration of impact):
http://baseball.physics.illinois.edu/grip.html
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Old 01-26-2019, 01:09 PM
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Quote:
Originally Posted by Chronos View Post
Speaking abstractly, the bat would be almost like an unanchored object, but the batter is still exerting some nonzero force, and imparting some nonzero work, during the brief duration of the collision, so there would be some slight advantage to the bigger batter.
Not necessarily.
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Old 01-26-2019, 01:31 PM
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As someone who once played a level below semi-pro in men's slow-pitch softball, I think I can add some color. The mass of the bigger guy is likely to indeed play a role in determining who can get the bat up to speed faster. And yes, grip strength is very, very important -- if not critical -- in determining that. (The physics model here is a double-pendulum, with extreme forces placed on the second fulcrum point.)

Big, strong guys can 'force' and 'push' a bat through the zone, to be sure. But no big shot ever happened while the wrists were still locked down and holding on tight. A home run still? Sure. That happens all the time in the MLB. But you want to maximize things and truly let that bat fly? It's going way faster than your hands are when it hits the ball.

There's a reason people talk about it being 'effortless', or about hitting a 'sweet spot'. And there's also a reason that the big shots are pulls. It's because you see the ball coming and you have time to put all your physical things in motion and turn that energy plant as much as you can and extend those arms and hold on tight with the wrists and flail the head of the bat at that ball and hope -- hope! -- that it catches that ball square.

And when it does catch it square, it doesn't care if it came from a behemoth or a runt. It's just mass on mass, in a violent collision that will send the little guy (the ball) a long way away and slow the big guy (the bat) enough to make it not hurt the guy who swang it. My guess would be that 95+% of amatuer softball players never experience the feeling when they are fully extended and the bat is no longer a part of them and they are still touching it but it's doing what it will do. It takes a lot to have that kind of trust. But that's also what it takes to hit it over the fence. If that's what you want to do.
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Old 01-26-2019, 07:39 PM
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Originally Posted by RaftPeople View Post
Alan Nathan is a scientist that studies this stuff. Here's an article he posted about the batter's grip at impact has zero influence on the path of the ball (in summary: the wave generated by impact that travels to the knob of the bat and back to area of impact takes longer than the duration of impact):
http://baseball.physics.illinois.edu/grip.html
So, is this the final GQ answer? Does anyone have a better cite to the contrary?
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Old 01-28-2019, 03:45 PM
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What if the batters are standing on a treadmill?

[Sorry. I'll see myself out.]
  #25  
Old 01-28-2019, 04:51 PM
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So here's another thought experiment to toss in there.
2 motors with their axis vertical.
Each has a baseball bat attached to the motor shaft.
In A it's attached by a rigid steel bar.
In B it's simply attached by a piece of flexible cord.
Both motors are started and the bats speeds are met say around 75mph, both sweet spots equal distance from the motor shaft.
Baseball is shot at at 90mph at the sweet spot to make contact.
Which ball goes further?
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Old 01-28-2019, 09:05 PM
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From the cite that RaftPeople provided, my non-GQ guess is that it won't matter since it takes longer for the impact wave to get to the base of the bat and back to the ball than the ball is touching the bat. So, (to speak non-scientifically) by the time the bat "realizes" it's attached to a steel bar instead of a flexible cord, the ball is already gone.
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Old 01-29-2019, 12:05 PM
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Originally Posted by Hampshire View Post
So here's another thought experiment to toss in there.
2 motors with their axis vertical.
Each has a baseball bat attached to the motor shaft.
In A it's attached by a rigid steel bar.
In B it's simply attached by a piece of flexible cord.
Both motors are started and the bats speeds are met say around 75mph, both sweet spots equal distance from the motor shaft.
Baseball is shot at at 90mph at the sweet spot to make contact.
Which ball goes further?
It might be the same, but I don't think that's the instructive takeaway, if we are talking about any matters at all of real-life practicality. What will happen in the case presented in the OP is that the smaller/weaker guy won't really be able to get that bat up to the same speed as the other guy -- or in other words, his motor with vertical axis just won't turn as fast.

If we want to just talk about abstractions, then that's surely fine. But in the real-life scenarios, grip strength and mass and such matter.
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Old 01-29-2019, 03:01 PM
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Originally Posted by SayTwo View Post
It might be the same, but I don't think that's the instructive takeaway, if we are talking about any matters at all of real-life practicality. What will happen in the case presented in the OP is that the smaller/weaker guy won't really be able to get that bat up to the same speed as the other guy -- or in other words, his motor with vertical axis just won't turn as fast.

If we want to just talk about abstractions, then that's surely fine. But in the real-life scenarios, grip strength and mass and such matter.
I weigh about 180 pounds. I guarantee that a, say, 130 pound professional baseball player will be able to get the bat swinging faster than I can. The question is, if the bat is swinging at a certain speed, will it go further with the heavier batter. I think that's answered, and I'm not sure what your post added to that. Are you saying that it's impossible that a 100 pound guy will get a bat up the same speed as a 200 pound guy? Extra weight doesn't mean extra strength. Plus, the 200 pound guy could just put less effort into the swing -- we just need the bat speed to be the same.
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