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post #160
post #160
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Thanks for the heads-up. See my response...
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I am not disagreeing with Brian Gordon.
Am disagreeing with this formulation: (maybe it is just a problem of sematics...)
A greater racket drop increases the length of the acceleration path to impact. If achieving a greater effective arm length were important, one would have a straight arm backswing.A greater racket drop increases an effective arm length.
Only rotational momentum is proportional to an effective arm length. At the moment of impact, the effective arm length remains the same. The racket trajectory is very complex, and can not be reduced to rotational component only. When the rotational part starts, the effective arm length is unaltered.A force momentum is proportional to an effective arm length.Comment
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Just to close a topic a bit
Your post from TW
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I will try and summarize this thread. I was wondering if increasing the racket drop, by say, 6 inches would make much of a difference, seeing that the motion of the racket only starts to accelerate prior to impact about half way up from the point of maximum racket drop. I see now that it offers advantages, for the following reasons:
* The extent of the racket drop is somewhat analogous to arm pronation: by itself, it does not directly contribute to racket speed , but is an indication that your arm is nice and loose and that biomechanically you are properly loading all the necessary components of the kinetic chain for an optimal serve (extension of the legs, loose arm, movement of mass of the racket).
* The greater racket drop stabilizes the trajectory and sets the racket better in postion for the ensuing impact of the ball.
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I disagree with a phrase "the extent of the racket drop ....,it does not directly contribute to racket speed".Probably difference of opinions stems from a word "directly" above.
And again: a racket plus an arm form a lever.
IMHO: a longer lever translates into a higher speed at a contact.
Whether I can prove it is a different issue.
regards,
julianLast edited by uspta146749877; 10-28-2010, 09:54 AM.Comment
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Could you please define what you mean exactly? For example: when an ice skater twirling on ice, pulls in his/her arms, they speed up. When hitting a forehand, pulling the hand closer to the body during the stroke, results in more power and speed than keeping the arm stiff. When hitting a serve, the arm is extended, but the racket shaft is angled. In all of these cases, a shortening occurs. What do you define as "the lever"? Maybe just having trouble visualising what you mean...Originally posted by uspta146749877 View Post
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For Phil
Switching gears just for a second:
what are chances for you to get an access to a book
"Biomechanics of Advanced Tennis"?Comment
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forehand analogy MAYBE flawed
IMHO:Your remark about forehand maybe NOT always true.
Probably only Brian can resolve this issue-
it is an old bend/bend vs straight issueComment
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Pro talk vs Biomechanist talk
Quote:
A greater racket drop increases an effective arm length.
I just wonder if here we go again with vernacular vs. biomechanically correct. Better if Brian explains himself, but granted, the length of the lever arm is not literally changed by the length of the drop (although it may allow you to involve more core/torso rotation), but it is also true that the ball has no idea of the length of the lever arm that is hitting it; it only recognizes the velocity and momentum of the object striking it (including direction). The additional deeper racket drop allows you to accelerate the racket over a longer period of time and distance so that when the racket meets the ball, it has more velocity; in addition, the direction of the momentum can be better defined and directed by the player to suit his needs. In that way, the "effective" lever arm is increased. You may think you can only swing the racket so fast, but that is not true. Imagine how fast you could swing a badminton racket through the service hitting zone. Now realize that the "headstart" you get from the lower drop point changes the weight you have to accelerate from a tennis racket to a badminton racket. OK, it's a bit of a stretch, but I think you can see what I am getting at.
But the point John made in the article about getting into the "Pro drop" a little above the low point on a trajectory directly to the ball and on to the target is what counts. Until you get on that "track" to the target, you can't really accelerate the racket head to the ball effectively. The lower drop makes it easier for the player to get on that "track". And it will make a much smaller player appear much bigger like the big boys because he gets on that track early. In the "old days", the big guys (over 6'3", much less over 6'6") never had great motions like an Isner or Ivo. (I'm sure there were some exceptions, but they were very rare and if they could serve they couldn't do anything else for the most part.)
don
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Levers again
Just a quotation-Originally posted by uspta990770809 View PostQuote:
A greater racket drop increases an effective arm length.
I just wonder if here we go again with vernacular vs. biomechanically correct. Better if Brian explains himself, but granted, the length of the lever arm is not literally changed by the length of the drop (although it may allow you to involve more core/torso rotation), but it is also true that the ball has no idea of the length of the lever arm that is hitting it; it only recognizes the velocity and momentum of the object striking it (including direction). The additional deeper racket drop allows you to accelerate the racket over a longer period of time and distance so that when the racket meets the ball, it has more velocity; in addition, the direction of the momentum can be better defined and directed by the player to suit his needs. In that way, the "effective" lever arm is increased. You may think you can only swing the racket so fast, but that is not true. Imagine how fast you could swing a badminton racket through the service hitting zone. Now realize that the "headstart" you get from the lower drop point changes the weight you have to accelerate from a tennis racket to a badminton racket. OK, it's a bit of a stretch, but I think you can see what I am getting at.
But the point John made in the article about getting into the "Pro drop" a little above the low point on a trajectory directly to the ball and on to the target is what counts. Until you get on that "track" to the target, you can't really accelerate the racket head to the ball effectively. The lower drop makes it easier for the player to get on that "track". And it will make a much smaller player appear much bigger like the big boys because he gets on that track early. In the "old days", the big guys (over 6'3", much less over 6'6") never had great motions like an Isner or Ivo. (I'm sure there were some exceptions, but they were very rare and if they could serve they couldn't do anything else for the most part.)
don
Force and levers
The force applied (at end points of the lever) is proportional to the ratio of the length of the lever arm measured between the fulcrum (pivoting point) and application point of the force applied at each end of the lever.
Mathematically, this is expressed by M = Fd, where F is the force, d is the distance between the force and the fulcrum, and M is the turning force known as the moment or torque.Comment
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I don't disagree
Of course, that, as you should be the first to point out, is the physics of the force being applied by the player at the moment of impact. But the impact felt by the ball is a function of the momentum that is effectively transferred to it. I think it was my old coach, Jerry Alleyne, that used to say you hit the ball with the "free motion" and momentum of the racket. If it was really about how much leverage we could apply at any given moment in time, it would also require us to hold the racket as tight as possible. The mass of our bodies adds a certain amount of momentum to the momentum of the racket that hits the ball, but if that was really the case, the velocity of the ball would be much more closely proportional to the weight of the player (that is twice as fast for twice as heavy a player or twice as heavy an arm, etc). That simply is not the case, although it certainly is a factor. You get more speed by relaxing and releasing the speed of the racket.Originally posted by uspta146749877 View Post
donComment
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Sorry, you misunderstood me. I am not referring to what is a lever, and the equation for torque. I am referring to what phase of the serve does your increase of effective arm length apply? (not at impact - here nothing has changed since d is still the same)Originally posted by uspta146749877 View Post
I assume it is only a small part of the initial racket drop...
To say: in the above equation, I assume you are asserting that M has increased due to a phase of greater linear acceleration, because d at impact has not increased.Last edited by gzhpcu; 10-28-2010, 11:03 PM.Comment
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Saying the same thing
Okay. I think we are saying the same thing. In the differential instant before impact, the player must be applying a centripetal force equal to the centrifugal force exerted by the racket (remember that force actually lifts the player off the ground to a certain extent) and in that moment the lever arm has nothing to do with the deeper "Pro drop", but the player is able to exert a greater force because of the "phase of greater linear acceleration" that took place as a result of that "Pro drop". Bottom line, Phil, is that you can generate more racket head speed with the longer path to the ball of the "Pro drop", which I think is the answer to your original question.....(I think?!)Originally posted by gzhpcu View Post
awaiting the response of someone who actually knows the answer,
donComment
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Perhaps even more confused
Now that I think about it, in that moment the centripetal force does not involve the lever arm; it's just keeping the racket from flying away; so there is no great lever arm involved in holding on just before impact... somebody, help
donComment
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