one more episode of : yeah right weight transfer gives you power...

[MNPlayer]

Originally Posted by sureshs

I don't recall, but probably in TWU in some article there.

The running adds to the speed.

Let ground be the neutral frame of reference. Speed wrt ground = speed wrt to thrower + speed of thrower wrt ground (the car speed).

For the guy in a car, the speed at which he can throw is the same as if he is stationary. But when this gets added to the speed of the car, it becomes formidable. It has been documented by the police. The teenage boy did not realize how fast his missile was going because he thought it would be the same as the prank he played on his brother at home by throwing something at him.

This has also been documented by Newton. Motion is generally relative (excepting near the speed of light which we could have a fascinating discussion about, and forms the basis for special relativity). We are, after all, living on a roundish globe spinning 'round the sun, our shared "reference frame".

[nabrug]

Originally Posted by MNPlayer

Motion is generally relative.

Motion is relative.

Can you push off from the side of a swimming pool if the side of the pool doesn't move in your direction first?

V1 + V2 (+V3 etc.) = Vtot

[ATP100]

Originally Posted by ATP100

This thread proves it is very difficult to find a good teaching pro, and a student who will listen also.

I believe this even more.

[MNPlayer]

Originally Posted by nabrug

Motion is relative.

Can you push off from the side of a swimming pool if the side of the pool doesn't move in your direction first?

V1 + V2 (+V3 etc.) = Vtot

Well I was trying to make an exception for relativistic effects (the speed of light is a constant not relative to any reference frame) which I suppose can be ignored in tennis related calculation

http://en.wikipedia.org/wiki/Special_relativity

[bhupaes]

This topic has been discussed many times in different contexts, and this is the way I understand it, in simple terms.

The unwinding of a coiled body aided by the leg push off creates a lag in the arm and hand, loading the shoulder and arm muscles. The contraction of the stretched muscles, aided by the pull from the rotating body, accelerates the arm in the forward swing. My claim is that at this point, the body has transferred whatever energy it will to the hand/racquet system, and its only remaining function is to serve as a solid anchor from which the arm and hand can do their job to add more energy to the racquet. This is where the positioning of the arm becomes important - the hand body connection must be solid. If your arm is flailing wildly at this point, it will not have enough support from the body, and your shot will not feel solid. All the advice about how to position the hand/wrist correctly comes in at this point. Upper arm rotation and biceps contraction provide the main additional racquet head speed at this point, with ulnar to radial movement of wrist adding to spin and control (and some power, of course).

Actual forward movement of the body at contact time, in terms of MPH, is probably not contributing anything significant, and as long as it provides a solid base for the arm, it can be moving in any direction appropriate for the shot. In some very short strokes such as volleys and certain approach shots, I think body movement forwards probably ensures that the racquet goes through the range of motion that's necessary, and that the player is not standing in one spot and reaching forwards. Of course, such movement also helps the player get positioned early for the next shot, as we know.

[sureshs]

Originally Posted by MNPlayer

This has also been documented by Newton. Motion is generally relative (excepting near the speed of light which we could have a fascinating discussion about, and forms the basis for special relativity). We are, after all, living on a roundish globe spinning 'round the sun, our shared "reference frame".

Motion is also relative near the speed of light. The addition of velocities is not Galilean, but involves a non-linear term. It is still relative. Two high speed electron beams moving towards each other at 0.8c will not see a relative speed of 1.6c, but only 0.98c. So it is still relative and not the original speed of each.

It is only light, or photons in general, whose motion is not relative and the speed is always c.

[mightyrick]

Originally Posted by sureshs

When bodies are connected together, you cannot isolate one and say that is the only mass responsible. It has been shown that the "virtual racquet" extends up to the lower part of the forearm.

The momentum of the racquet is not separate from other momentum of the body. That is why cricket players runs many yards before bowling (pitching) the ball. The speed built up by the body also contributes to the speed of the ball. A rock thrown at someone by a crazed teenager from a moving car is far more devastating that one thrown by him if he was still.

I said "at the point of contact" the only mass directly involved is the racquet. The rest is all acceleration or momentum.

What I have said consistently about a hundred thousand times is that at every point in the stroke, there is a mass and an acceleration involved. In the entire chain, I contend that the mass at the beginning is actually the most impactful -- which is body weight itself.

[sureshs]

Originally Posted by mightyrick

I said "at the point of contact" the only mass directly involved is the racquet. The rest is all acceleration or momentum.

The point of contact is on the strings (unless you are like me and believe in using all that you paid for). Then why does the racquet mass come into play? Because the racquet is connected to the strings. In the same way, anything connected to the racquet also comes into play, in lesser and lesser amounts (like the mass of your head may not be significant). Otherwise only the mass of the string area in contact, which is negligible, would be the mass involved.

[salsainglesa]

weight is not mass, you have everything right, but that... and i am guessing its a just in the name that is colloquially used. but still its confusing.

[toly]

There are a lot of debates about optimum racquet mass and how much tennis player’s body mass should be behind the striking racquet.
Let’s assume:
Tennis boll has the mass 0.057 kg.
Vreal - is the speed of the ball after impact with the racket with real mass (real racquet).
Videal - is the ball speed after impact with the racket with infinite mass (ideal racquet).
Then, the tennis racquet mass efficiency can be expressed as:
K = Vreal/Videal.
I don’t want to write any more formulas here and show just result of calculation of racquet mass efficiency.


We can see from the diagram above, the racquet alone (0.3-0.4kg) can provide mass efficiency 84-87.5%. The racquet with hand (1-1.5kg) has efficiency 94-97%. The racquet mass efficiency with the arm would be more 98%.
Thus, the mass of the body behind the racquet is not so important. IMO, mass of the hand and forearm would be enough.

[mightyrick]

Argh, we're going in circles. I have to give up on this thread. Too many people are not understanding mechanical physics and I'm fairly sure that a single thread isn't going to properly educate people.

[5263]

Originally Posted by salsainglesa

weight is not mass, you have everything right, but that... and i am guessing its a just in the name that is colloquially used. but still its confusing.

not technically, but functionally in this context it can be used that way, as a certain mass will be a certain wt under our gravity, correct?

[5263]

Originally Posted by sureshs

The point of contact is on the strings (unless you are like me and believe in using all that you paid for). Then why does the racquet mass come into play? Because the racquet is connected to the strings. In the same way, anything connected to the racquet also comes into play, in lesser and lesser amounts (like the mass of your head may not be significant). Otherwise only the mass of the string area in contact, which is negligible, would be the mass involved.

I think your point here is very good.

[5263]

Originally Posted by toly

There are a lot of debates about optimum racquet mass and how much tennis player’s body mass should be behind the striking racquet.
Let’s assume:
Tennis boll has the mass 0.057 kg.
Vreal - is the speed of the ball after impact with the racket with real mass (real racquet).
Videal - is the ball speed after impact with the racket with infinite mass (ideal racquet).
Then, the tennis racquet mass efficiency can be expressed as:
K = Vreal/Videal.
I don’t want to write any more formulas here and show just result of calculation of racquet mass efficiency.


We can see from the diagram above, the racquet alone (0.3-0.4kg) can provide mass efficiency 84-87.5%. The racquet with hand (1-1.5kg) has efficiency 94-97%. The racquet mass efficiency with the arm would be more 98%.
Thus, the mass of the body behind the racquet is not so important. IMO, mass of the hand and forearm would be enough.

Does this prove Cross wrong, or just show how the racket is most of the mass (85%) needed?

Is the ref for this chart solid?
So more mass after a point does not matter much?

[papa]

How do you factor in the grip (how tight the racquet is being held), seems to be that this would be a critical factor and might negate/alter some of the calculations everyone is talking about.

Would everyone agree that the amount the racquet is "forced back" at impact is a factor of the speed/pace of the incoming shot, the weight of the racquet, the speed of the racquet coming forward at impact, trampoline effect of the strings, weight of the player - where/how does grip fit in (has to be a significant factor)?

Do all the equations take this into consideration and if so, how?

Isn't there also a "time" element involved - however small?

Just trying to understand the "practical" implications of what everyone is talking about.

[5263]

Originally Posted by papa

How do you factor in the grip (how tight the racquet is being held), seems to be that this would be a critical factor and might negate/alter some of the calculations everyone is talking about.

Would everyone agree that the amount the racquet is "forced back" at impact is a factor of the speed/pace of the incoming shot, the weight of the racquet, the speed of the racquet coming forward at impact, trampoline effect of the strings, weight of the player - where/how does grip fit in (has to be a significant factor)?

Do all the equations take this into consideration and if so, how?

Isn't there also a "time" element involved - however small?

Just trying to understand the "practical" implications of what everyone is talking about.

I think the calcs do take it into account by addressing max potential values and anything less than optimal grip would reflect by depressing the values.

I'm thinking the bold above is why accel is important, as this would suffer less at impact than just straight velocity I expect.

[dozu]

Originally Posted by toly

There are a lot of debates about optimum racquet mass and how much tennis player’s body mass should be behind the striking racquet.
Let’s assume:
Tennis boll has the mass 0.057 kg.
Vreal - is the speed of the ball after impact with the racket with real mass (real racquet).
Videal - is the ball speed after impact with the racket with infinite mass (ideal racquet).
Then, the tennis racquet mass efficiency can be expressed as:
K = Vreal/Videal.
I don’t want to write any more formulas here and show just result of calculation of racquet mass efficiency.


We can see from the diagram above, the racquet alone (0.3-0.4kg) can provide mass efficiency 84-87.5%. The racquet with hand (1-1.5kg) has efficiency 94-97%. The racquet mass efficiency with the arm would be more 98%.
Thus, the mass of the body behind the racquet is not so important. IMO, mass of the hand and forearm would be enough.

wow - this is the scientific way of saying - swing the HUMAN racket, not the graphite racket !

[MNPlayer]

Originally Posted by dozu

wow - this is the scientific way of saying - swing the HUMAN racket, not the graphite racket !

Huh? It's says the opposite...

[5263]

Originally Posted by MNPlayer

Huh? It's says the opposite...

I was sort of thinking the same, but I guess he is focused on the hand and arm addition aspect even though that seems to contribute very little as Cross states.

[5263]

Toly,
can you share the source of the chart and quality of data?
I'm not disputing it, but just would like to know who and how it was done.