# Please recommend a poly that just grabs the "bleep" out of the ball

#### travlerajm

##### Legend
Snapback is actually a misnomer.

In the 5ms that the ball is in contact with the string surface, it compresses and then decompresses.

In the case of a topspin groundstroke, the ball pulls downward on the mainstrings as it compresses.

Then as it decompresses, it starts to pull upward on the mains as the ball’s surface starts to move upward faster than the stringbed due to its rotational moment of inertia. If the main strings are locked, then they are not free to travel upward with the ball’s surface, so they will exert a downward frictional force on the ball. This downward frictional force limits topspin.

But if the mains are not locked, the downward frictional force acts for a much shorter period. This allows the ball’s surface to continue to accelerate longer, generating more ‘overspin’ before it leaves the stringbed, resulting in much higher rpm.

So strings that can ‘snap back’ do generate more topspin, but it has nothing to do with how fast the mains snap back when you pull down in them with your fingers.

#### Sean Sullivan

##### New User
Snapback is actually a misnomer.

In the 5ms that the ball is in contact with the string surface, it compresses and then decompresses.

In the case of a topspin groundstroke, the ball pulls downward on the mainstrings as it compresses.

Then as it decompresses, it starts to pull upward on the mains as the ball’s surface starts to move upward faster than the stringbed due to its rotational moment of inertia. If the main strings are locked, then they are not free to travel upward with the ball’s surface, so they will exert a downward frictional force on the ball. This downward frictional force limits topspin.

But if the mains are not locked, the downward frictional force acts for a much shorter period. This allows the ball’s surface to continue to accelerate longer, generating more ‘overspin’ before it leaves the stringbed, resulting in much higher rpm.

So strings that can ‘snap back’ do generate more topspin, but it has nothing to do with how fast the mains snap back when you pull down in them with your fingers.
Great explanation, thanks!

I think a lot of people see the ball and string bed as a furry sphere being brushed up upon by only the frictional forces of a flat plane of interwoven strings. But when you see what actually happens to the ball at impact, it might change how you consider the deformation, compression, rate of expansion, etc. of the ball and stringbed (in addition to friction) in determining the speed of rotation of the ball after impact.

This is a flat impact, but it gives you an idea of what’s really happening to the ball when it gets hit. The strings don’t simply brush and roll the ball. They compress it into a disk, then the massive inner air pressure surge, plus the rebound forces of the deformation of the strings and ball, all act to launch the ball while the frictional forces are simultaneously doing their thing to the “pancaked” ball.

We all see the end result when we actually hit, but there’s really a whole lot going on under the hood.

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#### Injured Again

##### Professional
Watch:

At about the 0:05 mark, there’s a great example of “this is not how materials work”. Here in slow mo, Fed’s racquet appears to be quite flexible. Now, try to distort your racquet with manual forces (by hand) to the same degree and let me know how it turns out for you. It’s almost as if the racquet has different “tolerable range of distortion” properties under the conditions of a high speed ball impact as compared to say “being placed in a vice and slowly bent”, but yeah, that’s just silly.

All I’m saying is that it’s possible that tennis strings, being less rigid than actual racquets, also distort/rebound to some degree upon real time impact that cannot be properly replicated by simply pushing them to the side slowly and letting go. And, this deformation of strings also has some impact on how spin is imparted to a ball during a full speed groundstroke.

People continue to be perfectly capable of designing things in spite of the fact that they don’t fully understand exactly how they work: aspirin, cloud computing, and tennis equipment being among them.
Sure you can manually bend that racquet to that shape, and it won't break. Just take a look at how many posts there have been on this forum about people who have shrunk their frame length by significant amounts using tension differentials.

More technically, read up on stress-strain diagrams. An understanding will show that the vast majority of materials, including those in frames, behave uniformly within their elastic regime. Stress-strain diagrams do **not** contain an axis showing the speed of the stress impulse, nor do properties like yield strength or ultimate strength contain constraints based on the speed of the stress. As a matter of fact, in many composite materials, you can obtain a greater elastic bending by slowly applying the stress, as a sudden stress can initiate a brittle fracture.

#### Injured Again

##### Professional
Snapback is actually a misnomer.

In the 5ms that the ball is in contact with the string surface, it compresses and then decompresses.

In the case of a topspin groundstroke, the ball pulls downward on the mainstrings as it compresses.

Then as it decompresses, it starts to pull upward on the mains as the ball’s surface starts to move upward faster than the stringbed due to its rotational moment of inertia. If the main strings are locked, then they are not free to travel upward with the ball’s surface, so they will exert a downward frictional force on the ball. This downward frictional force limits topspin.

But if the mains are not locked, the downward frictional force acts for a much shorter period. This allows the ball’s surface to continue to accelerate longer, generating more ‘overspin’ before it leaves the stringbed, resulting in much higher rpm.

So strings that can ‘snap back’ do generate more topspin, but it has nothing to do with how fast the mains snap back when you pull down in them with your fingers.
Is there a source, like Cross and Lindsey, who has photographic evidence this is what is occurring?

What about the downward displacement of the strings that initially occurs during the compression phase of the contact? You don't mention this but I am assuming you saying that a more locked stringbed allows less recovery of the deflected mains back to their original position while the string and ball are still frictionally locked to each other?

#### travlerajm

##### Legend
Is there a source, like Cross and Lindsey, who has photographic evidence this is what is occurring?

What about the downward displacement of the strings that initially occurs during the compression phase of the contact? You don't mention this but I am assuming you saying that a more locked stringbed allows less recovery of the deflected mains back to their original position while the string and ball are still frictionally locked to each other?
No that’s not what I wrote. There are more than a dozen articles published on this.

#### Injured Again

##### Professional
No that’s not what I wrote. There are more than a dozen articles published on this.
Can you post a link to one please? And if I'm reading into your response that you're not interested in having a conversation on this, then just let me know and it can stop.