trojansc
Legend
All-VolleyTalk 1st Team (2022, 2021, 2020, 2019, 2018, 2017), All-VolleyTalk 2nd Team (2016), 2021, 2019 Fantasy League Champion, 2020 Fantasy League Runner Up, 2022 2nd Runner Up
Posts: 28,106
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Post by trojansc on Mar 22, 2019 3:30:59 GMT -5
If you all are ready for the truth, let me know. I experimented. Tested just two variables: mass of attacker and armspeed of attacker. Measured impact force on ball, initial velocity of ball, impact force on a target ~7m from the point of contact, and the velocity at contact. Results: faster swing generally increases the force and velocity, larger attacker generally increases the force and velocity. Conclusion: "she hits a heavy ball" = she is a heavy girl. Disclaimer: tomclen's previous work much cited in my official report I have some evidence supporting your claim. Jupiter is the largest planet in the solar system, and I would assume has the most mass, correct? They always said those were some heavy hits!
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Post by n00b on Mar 22, 2019 6:50:11 GMT -5
Force = Mass x Acceleration
High mass is a heavy arm High acceleration is a fast arm
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Post by mikegarrison on Mar 22, 2019 9:58:20 GMT -5
In real life, the collision of a bat and a ball (or an arm and a ball) are "inelastic". That means that substantial energy is lost due to the deformation of the ball and the bat (or arm). This energy loss is measured by the coefficient of restitution. You all know that if you drop a volleyball to the floor then it won't bounce back up as high as where you dropped it from. It loses useful energy when it compresses and then uncompresses (some of the energy goes to heat). That's CoR.
The weight of the arm is a very minor factor compared to the energy that the arm is swung with. If you use the same energy to swing a heavy arm (or bat) versus a light one, the heavy one will swing slower. But both will compress the ball about the same -- the slower and heavier arm will input about the same amount of energy onto the ball as the faster and lighter one, because they were were both swung with the same energy to start with. But in real life, a heavier arm usually means more muscles, which usually means more energy to swing the arm with. So it's not so much the weight or speed of the arm as it is the energy used to put the arm into motion.
That energy is transferred to the ball, but some of it is lost due to the coefficient of restitution of the ball (and also the CoR of the arm, too). The remaining energy becomes speed and spin on the ball.
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Post by mikegarrison on Mar 22, 2019 11:38:55 GMT -5
In real life, the collision of a bat and a ball (or an arm and a ball) are "inelastic". That means that substantial energy is lost due to the deformation of the ball and the bat (or arm). This energy loss is measured by the coefficient of restitution. You all know that if you drop a volleyball to the floor then it won't bounce back up as high as where you dropped it from. It loses useful energy when it compresses and then uncompresses (some of the energy goes to heat). That's CoR. The weight of the arm is a very minor factor compared to the energy that the arm is swung with. If you use the same energy to swing a heavy arm (or bat) versus a light one, the heavy one will swing slower. But both will compress the ball about the same -- the slower and heavier arm will input about the same amount of energy onto the ball as the faster and lighter one, because they were were both swung with the same energy to start with. But in real life, a heavier arm usually means more muscles, which usually means more energy to swing the arm with. So it's not so much the weight or speed of the arm as it is the energy used to put the arm into motion. That energy is transferred to the ball, but some of it is lost due to the coefficient of restitution of the ball (and also the CoR of the arm, too). The remaining energy becomes speed and spin on the ball. There are limits to how fast a human can swing a bat or swing an arm, so weight is actually a major factor. There is a pretty narrow optimum range of power and weight. Give a major league power hitter a 10 ounce bat and they won't hit any home runs because they can't increase the bat speed enough to make up for the loss of mass. One study shows the ideal bat weight at roughly 32 to 34 ounces, with greatly diminished returns for weight above that and quickly losing exit velocity below that. Another factor is the deformation you referenced. Yes, there is energy loss, but there is a substantial percentage of energy that can be recovered. Since the ball is in the air (as opposed to bouncing on the ground), if the arm and ball lose contact at the point the ball is fully deformed, none of that energy is translated into forward momentum. If the hand can drive through the ball and maintain speed, then the ball will exit with more velocity. In baseball, consider a power hitter driving through the ball versus bunting where you hold the bat loosely and allow it to give some on impact. A heavier arm with a stronger muscle driving it through the impact will recover a greater percentage of the rebound than a lighter arm with less drive that slows on impact, even if the initial speed was slower. Empirically I know that I can serve a float on a line that will hit the back wall way beyond the endline and 20 feet high. I can take that same arm swing and "pop" the ball, and it will drop in the court. The difference? My hand stops abruptly and does not drive through the ball at all. We have all seen a server that just needs an "in" serve at a crucial point, and pushes the ball long. What happens? Maybe I'm wrong, but from observation I think they slow their arm swing down, but feel they should also avoid the abrupt "pop" on the ball and instead let their arm drive through the ball and it takes off long because they are now unintentionally recovering the energy from the deformation. I think you are mixing two different things. Yes, the ball has to take some time to rebound off the arm or bat, but that amount of time is very small and it very much is not the reason to "drive through" a hard hit ball. The reason for follow-through is because people who try to just swing to the contact point do not put all their available effort into the swing. The speed of the swing comes from the integrated force, and that means you should still be adding force all the way to the contact point. But if you swing "to make contact" rather than "to drive through the ball" you stop adding new force to the swing the closer and closer you get to the contact point. Your swing stops accelerating and can even start decelerating before you make contact. On the other hand, if you think "swing through the ball" then you continue to apply more force all the way and your swing accelerates all the way to the contact point. A float serve is an interesting case because, as you note, most volleyball players don't want to serve the ball as fast as possible, because it would go out of bounds. Thus, they *do* want to stop adding force before the contact once they reach the desired armspeed. That's why for the serve you try to slow your hand down to a target speed rather than just "drive through it". It's not really got anything to do with the amount of time it takes for the ball to rebound its shape. It has to do with the total amount of force you have accumulated into the swing. As for bat weights, yes, there is a range of most efficient bat weights and speeds, but it's because of biomechanical reasons that make those weights and speeds most effective for a human to add energy into the swing. So really it's still about how much energy you can put into the swing.
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Post by ineedajob on Mar 22, 2019 11:52:19 GMT -5
There are limits to how fast a human can swing a bat or swing an arm, so weight is actually a major factor. There is a pretty narrow optimum range of power and weight. Give a major league power hitter a 10 ounce bat and they won't hit any home runs because they can't increase the bat speed enough to make up for the loss of mass. One study shows the ideal bat weight at roughly 32 to 34 ounces, with greatly diminished returns for weight above that and quickly losing exit velocity below that. Another factor is the deformation you referenced. Yes, there is energy loss, but there is a substantial percentage of energy that can be recovered. Since the ball is in the air (as opposed to bouncing on the ground), if the arm and ball lose contact at the point the ball is fully deformed, none of that energy is translated into forward momentum. If the hand can drive through the ball and maintain speed, then the ball will exit with more velocity. In baseball, consider a power hitter driving through the ball versus bunting where you hold the bat loosely and allow it to give some on impact. A heavier arm with a stronger muscle driving it through the impact will recover a greater percentage of the rebound than a lighter arm with less drive that slows on impact, even if the initial speed was slower. Empirically I know that I can serve a float on a line that will hit the back wall way beyond the endline and 20 feet high. I can take that same arm swing and "pop" the ball, and it will drop in the court. The difference? My hand stops abruptly and does not drive through the ball at all. We have all seen a server that just needs an "in" serve at a crucial point, and pushes the ball long. What happens? Maybe I'm wrong, but from observation I think they slow their arm swing down, but feel they should also avoid the abrupt "pop" on the ball and instead let their arm drive through the ball and it takes off long because they are now unintentionally recovering the energy from the deformation. I think you are mixing two different things. Yes, the ball has to take some time to rebound off the arm or bat, but that amount of time is very small and it very much is not the reason to "drive through" a hard hit ball. The reason for follow-through is because people who try to just swing to the contact point do not put all their available effort into the swing. The speed of the swing comes from the integrated force, and that means you should still be adding force all the way to the contact point. But if you swing "to make contact" rather than "to drive through the ball" you stop adding new force to the swing the closer and closer you get to the contact point. Your swing stops accelerating and can even start decelerating before you make contact. On the other hand, if you think "swing through the ball" then you continue to apply more force all the way and your swing accelerates all the way to the contact point. A float serve is an interesting case because, as you note, most volleyball players don't want to serve the ball as fast as possible, because it would go out of bounds. Thus, they *do* want to stop adding force before the contact once they reach the desired armspeed. That's why for the serve you try to slow your hand down to a target speed rather than just "drive through it".It's not really got anything to do with the amount of time it takes for the ball to rebound its shape. It has to do with the total amount of force you have accumulated into the swing. As for bat weights, yes, there is a range of most efficient bat weights and speeds, but it's because of biomechanical reasons that make those weights and speeds most effective for a human to add energy into the swing. So really it's still about how much energy you can put into the swing. Alright, now that this is addressed... Why would you accelerate your arm to a speed beyond that with which you want to contact the ball, only to slow it down again? That, to me, sounds like you're putting undue stress on your shoulder. Why not just accelerate your arm to the speed with which you want to contact the ball and follow-through with that consistent speed?
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Post by mikegarrison on Mar 22, 2019 11:59:30 GMT -5
I think you are mixing two different things. Yes, the ball has to take some time to rebound off the arm or bat, but that amount of time is very small and it very much is not the reason to "drive through" a hard hit ball. The reason for follow-through is because people who try to just swing to the contact point do not put all their available effort into the swing. The speed of the swing comes from the integrated force, and that means you should still be adding force all the way to the contact point. But if you swing "to make contact" rather than "to drive through the ball" you stop adding new force to the swing the closer and closer you get to the contact point. Your swing stops accelerating and can even start decelerating before you make contact. On the other hand, if you think "swing through the ball" then you continue to apply more force all the way and your swing accelerates all the way to the contact point. A float serve is an interesting case because, as you note, most volleyball players don't want to serve the ball as fast as possible, because it would go out of bounds. Thus, they *do* want to stop adding force before the contact once they reach the desired armspeed. That's why for the serve you try to slow your hand down to a target speed rather than just "drive through it".It's not really got anything to do with the amount of time it takes for the ball to rebound its shape. It has to do with the total amount of force you have accumulated into the swing. As for bat weights, yes, there is a range of most efficient bat weights and speeds, but it's because of biomechanical reasons that make those weights and speeds most effective for a human to add energy into the swing. So really it's still about how much energy you can put into the swing. Alright, now that this is addressed... Why would you accelerate your arm to a speed beyond that with which you want to contact the ball, only to slow it down again? That, to me, sounds like you're putting undue stress on your shoulder. Why not just accelerate your arm to the speed with which you want to contact the ball and follow-through with that consistent speed? I meant "slow down" relative to how fast you *could* swing it, not swing faster and then slow down all in the same swing. But there are times for deception when you start your swing like it's going to be hard and then "take something off of it" to dink the ball in front of the back line defenders.
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Post by hammer on Mar 22, 2019 12:21:21 GMT -5
If you all are ready for the truth, let me know. I experimented. Tested just two variables: mass of attacker and armspeed of attacker. Measured impact force on ball, initial velocity of ball, impact force on a target ~7m from the point of contact, and the velocity at contact. Results: faster swing generally increases the force and velocity, larger attacker generally increases the force and velocity. Conclusion: "she hits a heavy ball" = she is a heavy girl. Disclaimer: tomclen's previous work much cited in my official report I have some evidence supporting your claim. Jupiter is the largest planet in the solar system, and I would assume has the most mass, correct? They always said those were some heavy hits! Love the size of your images -- keep up the good work!
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Post by mikegarrison on Mar 22, 2019 12:51:36 GMT -5
I think you are mixing two different things. Yes, the ball has to take some time to rebound off the arm or bat, but that amount of time is very small and it very much is not the reason to "drive through" a hard hit ball. The reason for follow-through is because people who try to just swing to the contact point do not put all their available effort into the swing. The speed of the swing comes from the integrated force, and that means you should still be adding force all the way to the contact point. But if you swing "to make contact" rather than "to drive through the ball" you stop adding new force to the swing the closer and closer you get to the contact point. Your swing stops accelerating and can even start decelerating before you make contact. On the other hand, if you think "swing through the ball" then you continue to apply more force all the way and your swing accelerates all the way to the contact point. A float serve is an interesting case because, as you note, most volleyball players don't want to serve the ball as fast as possible, because it would go out of bounds. Thus, they *do* want to stop adding force before the contact once they reach the desired armspeed. That's why for the serve you try to slow your hand down to a target speed rather than just "drive through it". It's not really got anything to do with the amount of time it takes for the ball to rebound its shape. It has to do with the total amount of force you have accumulated into the swing. As for bat weights, yes, there is a range of most efficient bat weights and speeds, but it's because of biomechanical reasons that make those weights and speeds most effective for a human to add energy into the swing. So really it's still about how much energy you can put into the swing. It is easy to demonstrate that there is more to driving through the ball than merely maintaining velocity until the point of contact. A really simple example is the difference between bunting a ball while holding the bat firm or bunting a ball while completely letting go of the bat before contact. The ball goes much faster forward if the bat is held firm and may not go forward at all if the bat is let go. I think you'll agree that the equation for the simple linear collision between the bat and ball is identical and that the force exerted by the hands on the bat did not change the velocity of the bat prior to the collision in any way. It has nothing to do with a loss of bat speed prior to the collision, since the bat speed is exactly the same in both cases. The difference is the force applied through the duration of the collision, which is the time of the deformation and the rebound. In fact, there was no force supplied at all UNTIL the initial point of impact. Well, yeah, but what does that have to do with anything? If you let the ball knock the bat back, then some of the energy of the collision that could go into rebounding the ball instead goes into moving the bat. But if you hold the bat in place (or throw the ball against a tree), then all the kinetic energy has to come away with the ball. So it bounces out farther. That has pretty much nothing to do with hitting a volleyball.
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Post by mikegarrison on Mar 22, 2019 15:20:02 GMT -5
Well, yeah, but what does that have to do with anything? If you let the ball knock the bat back, then some of the energy of the collision that could go into rebounding the ball instead goes into moving the bat. But if you hold the bat in place (or throw the ball against a tree), then all the kinetic energy has to come away with the ball. So it bounces out farther. That has pretty much nothing to do with hitting a volleyball. That is precisely the point. The same force that knocks the bat back is slowing the arm down. It doesn't matter whether the ball is moving or the bat is moving (or both). The frame of reference changes, but the physics stays exactly the same. Holding the bat is applying a force through the contact. Using your muscles to apply a force through the contact in volleyball is exactly the same. It has everything to do with hitting a volleyball. In fact, the time for deformation and rebound for a baseball is substantially less than the time of contact for a large air-filled volleyball which should make it MORE relevant not less. The physics don't change per sport. But that has NOTHING to do with the time of contact. In an ideal situation where the contact is instantaneous, the exact same thing applies for the bunted ball. The total kinetic energy after the collision is the kinetic energy of the ball plus the kinetic energy of the bat. So if the bat is moving after the collision, then the ball bounces less. That's it. Absolutely nothing to do with the time duration that the bat and ball are in contact with each other. This bunted ball thing has absolutely nothing to do with your claim that the arm has to be in contact with the ball longer for the ball to completely rebound.
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Post by universal on Mar 22, 2019 17:03:02 GMT -5
I offer this link for your consideration. A short recap of a volleyball wrist snap study presented by Peter Vint, former USOC Director of High Performance.
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Post by c4ndlelight on Mar 22, 2019 19:49:09 GMT -5
How often do we really hear about a "heavy" ball in volleyball separate from a hard-hit ball? Do people really report a difference? Maybe in tennis, but not so much in volleyball.
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Post by mikegarrison on Mar 23, 2019 7:42:04 GMT -5
How often do we really hear about a "heavy" ball in volleyball separate from a hard-hit ball? Do people really report a difference? Maybe in tennis, but not so much in volleyball. Well that's what I was trying to get at from the very start. If there is no difference in spin or speed of a "heavy" ball versus just a regular hard-hit ball, then "heaviness" is basically bullcrap. Maybe it's a reaction to a perception of the ball speed relative to the visual impression of the hitter, or maybe it's just purely a synonym for "hard hit". But either way, nothing about the hit itself is really "heavy". Or maybe "heavy" hits do exist -- hits that are harder to pop up than the typical hits at the same speed. If that's the case, then it seems to me the only possible variable that could be causing it is the spin rate of the ball. So if there really are "heavy hitters" who hit balls at the same speed an angle as other players but whose balls are really harder to pop up, then perhaps they are hitting them with a different spin rate than is typical.
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Post by sonofdogman on Mar 23, 2019 8:27:35 GMT -5
I confess that I have acted with a vulgar attitude on this one. Just trying to fit in, you know?
But if I may elevate things a bit, I have to say that if you're believing anyone other than mikegarrison then you're just as well believing that the sun revolves around the earth....
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Post by hochee on Mar 23, 2019 11:00:26 GMT -5
Per Mike (and physics), that ball is a little ambassador of the hitter because it is carrying her transferred energy. But heavy vs. light is also a function of the interaction of the ball with the receiving mass, the digger's platform, per spvb (and physics). If two balls travel at the same horizontal rate (same "mph"), does the one with a higher CoR/less spin carry more forward energy than the spinning one, which goes at the same rate because it slices through the air more efficiently? If so, maybe that forward energy is the thing that creates the "heavy" sensation? And/or, maybe the spinner bleeds more energy at impact with a stable platform? At any rate, that ball sure is promiscuous because it changes ambassadorial allegiances with each contact. Or maybe it is just Switzerland.
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Post by mikegarrison on Mar 23, 2019 16:27:05 GMT -5
@sbvb, the thing about physics is that all levels apply all the time. In any collision (elastic or inelastic), energy is conserved. In an elastic collision, however, some of that energy goes to heat. However, the basics are still the same.
In the case of the bunted baseball, here's what happens. The kinetic energy of the initial system = the kinetic energy of the final system - the energy lost to the CoR as heat. But the CoR of the bat and ball are basically fixed, so that lost energy is basically a constant. Now the initial kinetic energy is all due to the ball (1/2 m v^2) because the bat isn't moving. The final kinetic energy is split between the bat and the ball. If the bat isn't moving, then the ball has all of it. If the bat is moving, then the bat has some of it. If the bat has some of it, then the ball has to have less of it compared to the case where the ball has all of it.
So the reason the ball is bunted more firmly (more speed) if you hold the bat still rather than let it move backward is just because you have divided up a fixed amount of kinetic energy and put it all into the ball rather than letting the bat have some of it.
That's it. That's the explanation. There is no need to postulate anything more complicated.
As for the (swinging) batted ball, we can always analyze the bat with a free body diagram. It's not got anything to do with the speed of the bat. FBDs are just a way of isolating the relevant parts of the problem. Ignoring air drag and gravity, the places where forces may be acting on the bat at the collision are the hands and the ball. The actual physics of swinging a baseball bat are very complicated because the batter is pivoting, the wrists are pivoting, the arms are extending, the batter is stepping into the pitch, and the bat is pivoting relative to the hands -- it's not a very simple situation. The bat moves through space in a complicated way that only approximates an arc.
The further out on the bat the ball makes contact, the faster the bat is moving, so the more initial energy for the collision. But there is a spot on the bat several inches in from the end where the ball actually comes off the bat at the highest speed. That's because if the ball hits too close to the end of the bat then extra energy is lost in the flex of the bat. And yes, due to the internal forces when the bat bends after the collision there is one location (the center of percussion) where none of the force of the collision is transmitted back to the location the bat is being pivoted about. (But the reality of the swing is such that the bat's pivot point when making contact with the ball is not actually the hands.)
But anyway, we got onto this by talking about why you "swing through" a ball (a golf ball, a volleyball, a baseball, even chopping wood, whatever) rather than only trying to swing to the point of contact. And the main reason is that if people try to swing to the point of contact then they stop adding force/speed to the swing partway into it. It's just instinctive. But if they "swing through" it then they keep adding force all the way until the contact actually happens.
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