New at TWU: String Snap-back and Spin

[TW Professor]

A new experiment on the role of string movement and snap-back in the production of spin:

http://twu.tennis-warehouse.com/learning_center/stringmovementPart2.php

Bottom line: more movement = more spin.

 

[share1law]

A new experiment on the role of string movement and snap-back in the production of spin:

http://twu.tennis-warehouse.com/learning_center/stringmovementPart2.php

Bottom line: more movement = more spin.

I like this article, it emphasizes the importance of the friction between the string and ball.

But in another article posted in TWU
http://twu.tennis-warehouse.com/learning_center/COF.php
called: "Static Friction and Spin" clearly states that: "Ball-To-String Friction Does Not Matter", and only "String-To-String Friction Does Matter". It is pure BS and it contradicts with this new article. Could someone in TW please revise this article so all the conclusions and statements are consistent with each other?

 

[TimothyO]

A new experiment on the role of string movement and snap-back in the production of spin:

http://twu.tennis-warehouse.com/learning_center/stringmovementPart2.php

Bottom line: more movement = more spin.

I find the data and video fascinating.

But after trying numerous individual strings and hybrids I've also developed a layman's low tech, non-scientific test for string potential.

I call it the Squeeze Test.



Squeeze two mains together at various points around the string bed:

A: If there's no sound, no tiny vibrations in your fingers as the strings move across one another, your touch feels silky smooth or gel-like, and the mains eagerly and smoothly move back into their proper position on their own accord, then you probably have a powerful and very spin-friendly string bed.

B: If there's a creaking noise, you feel tiny vibrations in the strings and they move across one another, your touch feels rough and bumpy, and the mains remain stuck in their new position or reluctantly return to their positions, then you probably have only an average string bed.

Obviously there's more to it than that but after testing a bunch of different string beds I now get very excited when I pick up a racquet from the stringer and it behaves as described in paragraph A (and disappointed when it behaves as in B). Yesterday evening I picked such an A-type racquet (VS 16 Mains + FXP Power 16 Crosses) and was so pleased with the Squeeze Test that after dinner I zoomed down to the club to hit against a practice wall. Won't get to play until later this week due to weather, but initial results from hitting the wall and a few shots across the net bode well for this hybrid.

 

[julian]

Two articles

I like this article, it emphasizes the importance of the friction between the string and ball.

But in other article posted in TWU called: "Static Friction and Spin" clearly states that: "Ball-To-String Friction Does Not Matter", and only "String-To-String Friction Does Matter". It is pure BS and it contradicts with this new article. Could someone in TW please revise this article so all the conclusions and statements are consistent with each other?

You mentioned two articles in your post.
A silly question: who wrote a latter?(described by you as "OTHER")

 

[DavidNERODease]

Snap Back Test

Speaking of simple tests as indictors of stringbed performance... I use my finger tips to slide a main and then pull away quickly. Many new string jobs will "snap back" nicely but the real test is after you've played a few matches. Some string is truely superior in this manner - snapping back very quickly with a nice ping sound even after it has some miles on it. For me that has been an excellent real world indicator of the current condition of my string bed and of which string is truely better on the court. That being said TW data has really helped me (and my brother) settle on string for the 2011 season.

 

[Mig1NC]

I would like to see some hybrid setups taken through this battery of tests.

What happens when you run VS gut in the mains and Lux ALU Power in the crosses for example?

Does the slick cross give the main the ability to snap back faster as hinted in previous articles?

 

[TBrady]

Read this article and weep Breakpoint.

 

[Consolation]

I like this, it addresses a lot of issues.

There's still one glaring issue though.

The issue that bothers me is this:

If the string moves forward with the ball, then the relative speed of ball to the strings is diminished. Therefore, friction duration will be shorter because it it does not have to change the spin as much to bring it to the same speed as the ball's forward motion (which is also slowing due to friction) relative to the strings. This is a negative spin producing phenomenon.

And later this statement:

One thing that immediately pops out is that if there is no string movement, then the coefficient of friction between the ball and the string does not influence over-spin much, if any, but it does if there is string movement. In the latter case, the coefficient of friction influences how much the ball will grab and move the string and, then, how much the string will grab and spin the ball during its snap-back.

In a real swing there is always string movement. Even if the strings never move at all relative to each other (which is impossible), the entire racquet is moving. Even taking into account the loss of velocity during the hit, during a 5-6ms impact, the racquet, and thus the strings in the racquet, are going to move a lot. How much depends on the swing speed and racquet characteristics of course, but it is significant (for example using a 65mph tip speed and 40% plowthrough rating, the racquet/strings will move 10-14cm during impact).

My question is one of reference really. If you take the stringbed as your reference plane, than snap back clearly has the potential to add spin. But if you look at the moving racquet as the reference, is the snap back actually adding spin, or simply returning a portion of the energy that is lost due to the initial string deflection (as stated in the first statement above)?

Using a clamped racquet, the only possible source of tangential force is string snap back. Using a moving racquet, the movement of the entire stringbed provides tangential force. Is snap back able to return more tangential energy than is lost doe to the initial string deflection, or is it more a matter of minimizing losses (in other words maybe no string movement, meaning no initial lateral movement, is ideal).

 

[Fedace]

Do you have any way to measure which string has the best Ball Pocketing effect ?

 

[share1law]

You mentioned two articles in your post.
A silly question: who wrote a latter?(described by you as "OTHER")

It is on the TWU website.
http://twu.tennis-warehouse.com/learning_center/COF.php

 

[treo]

I haven't fully read the experiment and seems too scientific for me but the first video was very interesting. I've been doing my own real world experiments using "paired weaving" that weaves the crosses in pairs. Described here:
http://tt.tennis-warehouse.com/showthread.php?t=364060
The strings have much less friction and gets massive spin. 50lbs full poly with cheap Gosen Polyon on an OS Prince Bandit got lots of spin and comfort but lost tension quickly. 66lbs, comfortable, less spin but kept tension. 58-60lbs with a quality full poly might be the best. Shots hit near the frame tend to divebomb so I am going to try regular weaving on the outside 3 strings and paired weaving in the middle. Illegal stringing but a fun experiment that proves snap back gets more spin.

 

[julian]

Were BOTH papers written by the same AUTHOR?

It is on the TWU website.
http://twu.tennis-warehouse.com/learning_center/COF.php

Were BOTH papers written by the same AUTHOR?

 

[Don't Let It Bounce]

... Using a clamped racquet, the only possible source of tangential force is string snap back. Using a moving racquet, the movement of the entire stringbed provides tangential force. Is snap back able to return more tangential energy than is lost doe to the initial string deflection, or is it more a matter of minimizing losses (in other words maybe no string movement, meaning no initial lateral movement, is ideal).

Fair question, at least as far as I can tell. Short of any data to point to, it seems like we could use as a guide the perpendicular-to-itself movement of the string bed (i.e., the flat element of the shot). The energy returned by the string bed is apparently greater than what would be added by the forward movement of the racquet during ball-string contact if the string bed didn't absorb any in the first place. (I think that's the crux of what you're thinking about; let me know if we're thinking of two different things.) Thus, a strung racquet gives more rebound power than a nearly non-elastic solid paddle.

So, does this back-to-front power boost transfer to the low-to-high movement? My gut (heh) reaction is that it does, but tossing inter-string friction (for which there is no back-to-front analog) into the mix does seem to complicate things, as I think you are saying. It implies no contradiction to say that snap-back is delayed and/or reduced enough by that friction for the racquet movement to catch up to it, but it seems somehow counterintuitive, like maybe the last decade's big migration at the top of the game to co-polys would instead have been an earlier migration to something like really tight kevlar or steel, and string savers with micro-spikes – whatever would move least.

I don't have the physics background to be sure of any of this; just kinda dumping thoughts onto the keyboard. It's an interesting topic.

 

[Kevo]

I'd like to see what the variability is with an 18x20 pattern.

 

[share1law]

Were BOTH papers written by the same AUTHOR?

Why is it relevant? They are all published by the TWU and TWU needs to ensure its accuracy. One says the friction between the string and ball does not matter, which is BS. The other says the higher friction between the ball and string can move the strings farther, and when they snaps back, generate more spin, which I agree totally.

The point is, if TW calls itself a university, it needs to meet the expectation. Many people out there are blindly quoting what TWU articles say and consider what TWU articles golden rules.

 

[julian]

If a glass is half empty ...?

Why is it relevant? They are all published by the TWU and TWU needs to ensure its accuracy. One says the friction between the string and ball does not matter, which is BS. The other says the higher friction between the ball and string can move the strings farther, and when they snaps back, generate more spin, which I agree totally.

The point is, if TW calls itself a university, it needs to meet the expectation. Many people out there are blindly quoting what TWU articles say and consider what TWU articles golden rules.

I am hoping for some feedback from an OP,
regards,
julian

 

[Bedrock]

A new experiment on the role of string movement and snap-back in the production of spin:

http://twu.tennis-warehouse.com/learning_center/stringmovementPart2.php

Bottom line: more movement = more spin.

Just another myth.
It is more a sign of incorrect setup.

 

[TBrady]

Just another myth.
It more a sign of incorrect setup.

Wrong dude. Lets hear your scientific rebuttal.

 

[Bedrock]

Wrong dude. Lets hear your scientific rebuttal.

There is nothing to rebut.
It is like saying Control on strings package means No Control.
(But nodoby cares about true meaning)
Or like calling k90 a low power frame

 

[TW Professor]

I like this article, it emphasizes the importance of the friction between the string and ball.

But in another article posted in TWU
http://twu.tennis-warehouse.com/learning_center/COF.php
called: "Static Friction and Spin" clearly states that: "Ball-To-String Friction Does Not Matter", and only "String-To-String Friction Does Matter". It is pure BS and it contradicts with this new article. Could someone in TW please revise this article so all the conclusions and statements are consistent with each other?

The article has been substantially revised. The key distinction as to whether ball-to-string friction matters in the spin difference between strings is whether or not the strings move. If strings move, it matters. If they do not, it doesn't.

I think the two articles are up-to-date and in agreement now.

 

[TW Professor]

I like this, it addresses a lot of issues.

There's still one glaring issue though.

The issue that bothers me is this:



And later this statement:



In a real swing there is always string movement. Even if the strings never move at all relative to each other (which is impossible), the entire racquet is moving. Even taking into account the loss of velocity during the hit, during a 5-6ms impact, the racquet, and thus the strings in the racquet, are going to move a lot. How much depends on the swing speed and racquet characteristics of course, but it is significant (for example using a 65mph tip speed and 40% plowthrough rating, the racquet/strings will move 10-14cm during impact).

My question is one of reference really. If you take the stringbed as your reference plane, than snap back clearly has the potential to add spin. But if you look at the moving racquet as the reference, is the snap back actually adding spin, or simply returning a portion of the energy that is lost due to the initial string deflection (as stated in the first statement above)?

Using a clamped racquet, the only possible source of tangential force is string snap back. Using a moving racquet, the movement of the entire stringbed provides tangential force. Is snap back able to return more tangential energy than is lost doe to the initial string deflection, or is it more a matter of minimizing losses (in other words maybe no string movement, meaning no initial lateral movement, is ideal).

It is the relative speed of the contact point of the ball and the strings that matters. The relative speed is composed of the ball velocity parallel to the strings, the rotational speed and direction of the ball at its contact with the strings, and the speed of the strings/racquet parallel to the ball. The relationship does not care whether the racquet speed is 0 or 100 mph; or whether the ball is 0 or 100; or any other combination.

If the ball impacts with backspin to the racquet, as it usually does, then the relative speed of ball to strings will be ball speed at the center of mass plus rotational speed at the bottom of the ball plus the racquet speed parallel to the ball, all considered as positive numbers. The relative speed will determine how long friction must act to slow the ball parallel to strings and change the spin in the opposite direction until the relative speed of the bottom the the ball and racquet equals zero, at which point the ball is said to bite the strings. It does this the same way whether the relative speed is caused by the ball alone (clamped racquet), racquet alone (stationary ball--e.g., serve), or a combination of each (groundstroke).

Friction duration just cares about the relative speeds. The magnitude of the friction force will indeed depend on whether the racquet is clamped or swinging or the ball stationary or moving, or a combination. But whether it is a big friction force or a small one, they both act until biting occurs, at which point the spin will be about the same, even though they take different amounts of time to achieve this. But a moving racquet does not add and special tangential force. That force is friction and friction will act until the ball bites. The fast moving racquet will increase the normal force which will increase the friction force, but, again, that will terminate upon biting.

When strings move out of position they store tangential elastic energy. Thus, we then have two tangential forces: friction and elastic. Friction will both reverse the spin of the ball and move the string, storing some otherwise wasted tangential energy. When the ball bites, the friction terminates but the elastic energy is still available to spin the ball. Friction again will contribute by determining the snap-back string's grip on the ball.

In fact, friction is again the main actor. As the string begins to snap back, that once again increases the relative speed of string to ball and friction will then again start pushing against this motion and spinning the ball at the same time. The elastic energy stored in the string is transferred to the ball via friction.

 

[julian]

For TW Professor

It would be good if you would visit this POST from time to time.
Thank you
Julian

 

[julian]

Can we agree on terminology,please

It is the relative speed of the contact point of the ball and the strings that matters. The relative speed is composed of the ball velocity parallel to the strings, the rotational speed and direction of the ball at its contact with the strings, and the speed of the strings/racquet parallel to the ball. The relationship does not care whether the racquet speed is 0 or 100 mph; or whether the ball is 0 or 100; or any other combination.

If the ball impacts with backspin to the racquet, as it usually does, then the relative speed of ball to strings will be ball speed at the center of mass plus rotational speed at the bottom of the ball plus the racquet speed parallel to the ball, all considered as positive numbers. The relative speed will determine how long friction must act to slow the ball parallel to strings and change the spin in the opposite direction until the relative speed of the bottom the the ball and racquet equals zero, at which point the ball is said to bite the strings. It does this the same way whether the relative speed is caused by the ball alone (clamped racquet), racquet alone (stationary ball--e.g., serve), or a combination of each (groundstroke).

Friction duration just cares about the relative speeds. The magnitude of the friction force will indeed depend on whether the racquet is clamped or swinging or the ball stationary or moving, or a combination. But whether it is a big friction force or a small one, they both act until biting occurs, at which point the spin will be about the same, even though they take different amounts of time to achieve this. But a moving racquet does not add and special tangential force. That force is friction and friction will act until the ball bites. The fast moving racquet will increase the normal force which will increase the friction force, but, again, that will terminate upon biting.

When strings move out of position they store tangential elastic energy. Thus, we then have two tangential forces: friction and elastic. Friction will both reverse the spin of the ball and move the string, storing some otherwise wasted tangential energy. When the ball bites, the friction terminates but the elastic energy is still available to spin the ball. Friction again will contribute by determining the snap-back string's grip on the ball.

In fact, friction is again the main actor. As the string begins to snap back, that once again increases the relative speed of string to ball and friction will then again start pushing against this motion and spinning the ball at the same time. The elastic energy stored in the string is transferred to the ball via friction.

You said above
"If the ball impact with a backspin to the racket ..."
A simple question:
If I hit a TOPSPIN serve do you call it A BACKSPIN as well?

 

[TW Professor]

You said above
"If the ball impact with a backspin to the racket ..."
A simple question:
If I hit a TOPSPIN serve do you call it A BACKSPIN as well?

In general, whatever shot you hit, when it bounces from the court it has topspin (except extreme circumstances)--more if you hit a topspin shot, less if you hit a slice. This is topspin in the frame of reference to the court. Looking from the side of the court and in comparison to the court, for example, the top of the ball is spinning in the same direction as the forward motion of the center of mass of the ball. When you swing low to high for a topspin shot, the ball will travel across the strings (actually down the strings). In that case, the top of the ball (compared to the strings--i.e., tilt your head perpendicular) is spinning up the racquet and ball's center of mass is moving down the racquet--i.e., backspin. Or, perhaps this is easier to remember: if at the contact point of the ball with its surface (court or strings) the direction of spin and of translation is the same, then it is backspin to the surface. If the directions are opposite, it is topspin.

 

[Bedrock]

In general, whatever shot you hit, when it bounces from the court it has topspin (except extreme circumstances)--more if you hit a topspin shot, less if you hit a slice. This is topspin in the frame of reference to the court. Looking from the side of the court and in comparison to the court, for example, the top of the ball is spinning in the same direction as the forward motion of the center of mass of the ball. When you swing low to high for a topspin shot, the ball will travel across the strings (actually down the strings). In that case, the top of the ball (compared to the strings--i.e., tilt your head perpendicular) is spinning up the racquet and ball's center of mass is moving down the racquet--i.e., backspin. Or, perhaps this is easier to remember: if at the contact point of the ball with its surface (court or strings) the direction of spin and of translation is the same, then it is backspin to the surface. If the directions are opposite, it is topspin.

whatever shot you hit, when it bounces from the court it has topspin This is way too general.

 

[TW Professor]

whatever shot you hit, when it bounces from the court it has topspin This is way too general.

It's meant to be: When a ball bounces off the court it will have topspin to the court, unless it is a drop shot where the spin speed is faster than the forward speed and the angle of impact is almost vertical. Then friction may not be enough to turn the spin around into topspin and the ball may even bounce backward with, now, backspin to the receiver's side of the court. But, in general, 99% of the time, the ball will have topspin to the court.

It gets more complicated with respect to the receiver's racquet. A few examples: When the ball has topspin to the court does it have backspin to a fast, upward swinging stroke? Yes. But what if you hit a fast rising ball with a slower moving upward stroke, then the ball is moving up the strings, as is the spin direction at the top of the ball, so the incident spin is topspin to the racquet.

If I hit a topspin serve, will it be backspin to the receiver's racquet if he tries to return topspin? Yes. What if he returns a slice? Then no. If the ball is hit on the rise and the racquet is slicing down, then the direction of the ball is up the racquet and the direction of the inbound spin relative to the racquet is also up the racquet, so it is topspin to the racquet. What if I hit a slice of a dropping ball? Then, if the racquet is slicing down faster than the ball is dropping, then the ball is still traveling up compared to the racquet and the spin is also up so the ball has topspin to the racquet (this is even though both racquet and ball are dropping in the court frame of reference). If the ball is dropping faster than the slicing racquet, then the ball is moving down the racquet, the top of the ball is moving toward the top of the racquet, and it is thus backspin to the racquet.

It obviously can be complicated and counter-intuitive. If you go to the Shot Maker Program: http://twu.tennis-warehouse.com/cgi-bin/trajectory_maker.cgi and input your shot parameters, you can see the calculated spin and speed directions relative to the racquet if you scroll down to the "Spin Analysis Section."

 

[TW Professor]

Another tool to help understand the relationships between incoming and outgoing spin, speed, and angle is the Shot Helper tool: http://twu.tennis-warehouse.com/learning_center/trajectories/trajectories.php (hmmm, poor tool name...I should come up with a better name for the tool.)

This tool allows you first to choose either a topspin or a slice shot. Then you can choose to see any of how the outgoing parameters of spin, speed, angle, and distance relates to the incoming parameters of ball speed, spin, and angle in and racquet speed, angle, tilt and impact location.

It's a good tool for understanding these relationships.

 

[sureshs]

Was Breakpoint right or wrong?

In any case, the arguments with Breaky are what probably lead to the new studies.

As scientists of Einstein's era said, even when Einstein was wrong, arguing with him (Einstein, not Breaky) forced them to justify their correctness better!

 

[Consolation]

It is the relative speed of the contact point of the ball and the strings that matters. The relative speed is composed of the ball velocity parallel to the strings, the rotational speed and direction of the ball at its contact with the strings, and the speed of the strings/racquet parallel to the ball. The relationship does not care whether the racquet speed is 0 or 100 mph; or whether the ball is 0 or 100; or any other combination.

If the ball impacts with backspin to the racquet, as it usually does, then the relative speed of ball to strings will be ball speed at the center of mass plus rotational speed at the bottom of the ball plus the racquet speed parallel to the ball, all considered as positive numbers. The relative speed will determine how long friction must act to slow the ball parallel to strings and change the spin in the opposite direction until the relative speed of the bottom the the ball and racquet equals zero, at which point the ball is said to bite the strings. It does this the same way whether the relative speed is caused by the ball alone (clamped racquet), racquet alone (stationary ball--e.g., serve), or a combination of each (groundstroke).

Friction duration just cares about the relative speeds. The magnitude of the friction force will indeed depend on whether the racquet is clamped or swinging or the ball stationary or moving, or a combination. But whether it is a big friction force or a small one, they both act until biting occurs, at which point the spin will be about the same, even though they take different amounts of time to achieve this. But a moving racquet does not add and special tangential force. That force is friction and friction will act until the ball bites. The fast moving racquet will increase the normal force which will increase the friction force, but, again, that will terminate upon biting.

When strings move out of position they store tangential elastic energy. Thus, we then have two tangential forces: friction and elastic. Friction will both reverse the spin of the ball and move the string, storing some otherwise wasted tangential energy. When the ball bites, the friction terminates but the elastic energy is still available to spin the ball. Friction again will contribute by determining the snap-back string's grip on the ball.

In fact, friction is again the main actor. As the string begins to snap back, that once again increases the relative speed of string to ball and friction will then again start pushing against this motion and spinning the ball at the same time. The elastic energy stored in the string is transferred to the ball via friction.

The 2 bolded parts. The moving racquet does add a tangential force, assuming it is not a linear impact. Even when the ball is imbedded, the moving racquet will apply a rotational torque to the elastic ball material. String deflection will result in less rotational torque being applied from the swing, assuming string/ball friction is adequate. As the ball begins to leave, the strings continue to move tangentially accross the ball. Snap back can increase the relative speed of the string to ball, but even without snap back, there is still a speed difference.

A perfectly rigid string bed, say a wooden paddle with linear cut-outs, will still result in very large amounts of topspin if the racquet swing path is glancing (as anyone who has ever played table tennis or paddle tennis can attest).

My question is really very simple. Compared to a hypothetical rigid stringbed, is the loss of potential rotational torque due to string deflection more than made up for by the string subsequently snapping back. If I hypothesize that it is not, then the results would still be that a string that snaps back 'correctly' will result in more spin. But in this case it's not because it's adding spin, it's simply recovering more of the lost spin. The difference has practical implications because it results in markedly different characteristics to maximize spin. This is important when you try to make a rule that will predict results for an unknown string.

 

[Bedrock]

But what if you hit a fast rising ball with a slower moving upward stroke, then the ball is moving up the strings, as is the spin direction at the top of the ball, so the incident spin is topspin to the racquet. - It is just a masterpiece. Give me some more.

 

[julian]

An author,PLEASE

But what if you hit a fast rising ball with a slower moving upward stroke, then the ball is moving up the strings, as is the spin direction at the top of the ball, so the incident spin is topspin to the racquet. - It is just a masterpiece. Give me some more.

Who is an author of a quotation?

 

[Bedrock]

There are only two parameters we are looking for (from strings bed) to improve the spin potential: Dwell time(duration of strings/ball contact) and friction.
It is more efficient to have main and cross strings deform proportionally without breaking normal uniform than allowing one of the string move more than another.
The snapping back does not increase dwell time and does not change friction itself.
It is just a special case of setup (unbalanced one)

 

[TimothyO]

The snapping back does not increase dwell time and does not change friction itself.
It is just a special case of setup (unbalanced one)

Bedrock...would you explain the "unbalanced" comment? It sounds interesting but, being a tennis noob, I have no idea what it means!

 

[share1law]

The article has been substantially revised. The key distinction as to whether ball-to-string friction matters in the spin difference between strings is whether or not the strings move. If strings move, it matters. If they do not, it doesn't.

I think the two articles are up-to-date and in agreement now.

Thanks for updating the articles. But the main strings always move during a normal ground stroke or serve. Some of them move and snap back more than others depends on inter-string friction and string/ball friction.

 

[share1law]

There are only two parameters we are looking for (from strings bed) to improve the spin potential: Dwell time(duration of strings/ball contact) and friction.
It is more efficient to have main and cross strings deform proportionally without breaking normal uniform than allowing one of the string move more than another.
The snapping back does not increase dwell time and does not change friction itself.
It is just a special case of setup (unbalanced one)

When the mains slide over the cross, the more they slide, the longer the dwell time will be. It works just like the spaghetti stringing system. ITF banned the spaghetti stringing system, but the smooth polys just work in the similiar way.