I need a clear answer, when receiving, when does the ball has LESS spin? Off the bounce? Or after it reached its apex?

[The Omega Man]

I am receiving conflicting information on this, some friends at the club told me it is off the bounce due to the ball briefly slowing down by the contact with the table before the law of physics make it resume its spinning and force, a friend told me that's why so many pro players like Truls just give the ball a quick zap to the ball the very instant it bounces.

Then some people say the ball loses spin exponentially the more I wait to hit it, I am talking serves receives here, so that would be around when the ball starts to go down?

Which one is it? Using the laws of physics and inertia, when am I LESS susceptible to the spin from a serve? When does the ball has less spin after a serve?

For the sake of this question, let's assume I am talking about a short/half long serve regular pendulum serve type of serve.

Any clear answer on this?

 

[sebi]

The ball has less spin the longer it travels.
So after the bounce spin -> apex less spin -> after apex even less spin.

But there is very little difference, because the spin only gets slowed down by the air resistance. I bet it's so little it might just be 1rpm or less

 

[Infernal]

The ball loses spin when it bounces on the table (backspin serves lose the most spin), but it does not stop spinning.

Time in the air does not change the spin much. Pros return the ball off the bounce for different reasons (can drop short, the ball is rising, so you get a better angle on the racket, better angles if you want to go wide, less time for your opponent, etc), not because "zomg the ball has no spin off the bounce" .

 

[sebi]

The ball loses spin when it bounces on the table (backspin serves lose the most spin), but it does not stop spinning.

And it does not spin back up, the spin it loses on impact is lost and does not magically come back. After the bounce the spin is pretty consistent

 

[NextLevel]

I am receiving conflicting information on this, some friends at the club told me it is off the bounce due to the ball briefly slowing down by the contact with the table before the law of physics make it resume its spinning and force, a friend told me that's why so many pro players like Truls just give the ball a quick zap to the ball the very instant it bounces.

Then some people say the ball loses spin exponentially the more I wait to hit it, I am talking serves receives here, so that would be around when the ball starts to go down?

Which one is it? Using the laws of physics and inertia, when am I LESS susceptible to the spin from a serve? When does the ball has less spin after a serve?

For the sake of this question, let's assume I am talking about a short/half long serve regular pendulum serve type of serve.

Any clear answer on this?

People make all kinds of statements about the physics of table tennis that are really comments on their experience of how difficult it is to do things with balls at certain points in the travel trajectory and are far less about physics. That's why I laugh at where you are coming from, these kinds of statements are made by great coaches and are often useless. Issues with serve return are far less about spin susceptibility and far more about how easy it is to *read* spin and contact the ball at certain points in its trajectory to produce a certain effect.

 

[thisisit]

qualitatively, you'll find the answer in middle school physics books.
quantitatively, you'll need undergrad mechanics+fluid dynamics.

 

[NetProphet]

I am receiving conflicting information on this, some friends at the club told me it is off the bounce due to the ball briefly slowing down by the contact with the table before the law of physics make it resume its spinning and force, a friend told me that's why so many pro players like Truls just give the ball a quick zap to the ball the very instant it bounces.

Taking the ball from the bounce is not easier because of less spin, it can be easier because the acceleration of the ball just after the bounce needs a different technique when contacting, because it has its maximum upward speed at this point, before it slows and begins to drop again.
This means you have to impart less force on the ball to achieve the distance you want and so it can allow greater/different possibilities for control.
I'm not able to explain it very well but if you've ever played football/soccer it's similar to striking the football on the half volley, just after bounce. Or rugby with the dropkick. You can just hit the ball harder because of the energy the ball has (from its bounce) as it contacts your foot.
Same for TT, kinda. But the ball still has it's (mostly) full spin.

Then some people say the ball loses spin exponentially the more I wait to hit it, I am talking serves receives here, so that would be around when the ball starts to go down?

My coach has told me this several times. Longer you wait on long balls = less spin on the ball. But my coach is an ex pro with European medals so he can read spin so easily that we're not even talking the same language when it comes to dealing with spinny balls. Altho, he played in the celluloid ball era so maybe it mattered more then??

I can't quantify how much spin the ball loses due to air resistance slowing it's spin rate. For him it seems to matter and he can probably calibrate for it.
I absolutely cannot, backspin is pretty much backspin for me.
I can calibrate to maybe 3 notches; lots medium and little but not anything in between. He probably has 9 degrees of calibration so for him waiting or not makes an actual difference to the technique/shot he'll play but for most of us I reckon forget it.
It stands to reason that the ball loses some spin the longer it travels - it can't spin forever eh - but I just treat a heavy backspin serve as heavy backspin whether I take it early or late. 🤷

 

[RefereeNumber2]

The short, direct answer to your question is that the spin decreases slightly over time as the ball travels through the air, due to friction. So the spin will be slightly weaker if you hit the ball later rather than earlier. But, in my opinion, this effect matters much less than other factors. The timing matters much more for 1) the position of the ball (height and length), 2) your own ability to move into position to play the shot you want, and a distant 3) the speed of the ball, which also decreases over time due to air resistance.

The advantage of taking the serve return early has much more to do with the position of the ball, e.g., it's easier to keep the return low if you hit the ball when it's low. Since this can help with neutralizing whatever spin is on the ball, some players/coaches may internally conceptualize this as there being "less spin", but in reality the RPMs are not actually lower.

Contact with the table tends to reduce the spin on very spinny shots, but there are some instances where it can slightly increase the spin on the ball, e.g., giving a no-spin ball a small amount of topspin.

 

[M4rc0H]

It is incorrect that the ball loses a significant amount of spin over time. Over the distance of the table, the ball loses about 5% of its spin and 35% of its speed (spinsight measurements). I think the reduced speed is the reason why people believe that the ball loses a significant amount of spin. You simply have more time to position yourself correctly and execute the technique correctly.

 

[Dr Evil]

...off the bounce due to the ball briefly slowing down by the contact with the table before the law of physics make it resume its spinning and force...

False. After contact, the ball continuously loses speed and spin because of friction with the air and table.

Then some people say the ball loses spin exponentially the more I wait to hit it...

True. At least in the air the spin decay is essentially exponential because the torque from air drag is proportional to the angular velocity. Off the bounce it's not exponential; it’s more like a one step reduction determined by the ratio of tangential to normal forces at impact and the coefficient of friction.

...so that would be around when the ball starts to go down?

No, spin decay is continuous from the moment the server contacts the ball. The longer you wait, the less spin it will have.

...when am I LESS susceptible to the spin from a serve?

If you want the least possible spin, then hit the ball at the last possible moment (just before it bounces twice on your side). But there's more to it than just the spin. There's also the direction the ball is moving when you hit it. For example, if it's moving up (off the bounce) then you get the benefit of its upward momentum which will somewhat counteract the downward deflection of an underspin serve.

 

[PhoenixTT]

The law of conservation of angular momentum states the following:
1. Rotation will not speed up unless additional force makes it speed up. So the spin will be slower at the apex as compared to immediately after the bounce. Especially since some of the spin is eaten up by contact with the table and changing the momentum (direction) of the ball.

2. HOWEVER, Newton, Decartes, Bernoulli, Euler, and Einstein all do not play TT. Otherwise they would have added the exception: due to special relativity, the spin speeds up the moment it hits your racket in an amount inversely proportional to your ITTF rating (the lower your rating, the more it spins faster, because the ball hates you).

 

[ttarc]

The law of conservation of angular momentum states the following:
1. Rotation will not speed up unless additional force makes it speed up. So the spin will be slower at the apex as compared to immediately after the bounce. Especially since some of the spin is eaten up by contact with the table and changing the momentum (direction) of the ball.

Some data for topspin balls (not serves) showing this can be found in:
Speed and spin differences between the old celluloid versus new plastic table tennis balls and the effect on the kinematic responses of elite versus sub-elite players

View of Speed and spin differences between the old celluloid versus new plastic table tennis balls and the effect on the kinematic responses of elite versus sub-elite players

journal.racketsportscience.org

Table 1
1. Exit from machine: speed 7.56 m/s, spin 60.67 rps
2. Before ball-table impact (just before impact): speed 5.53 m/s, spin 57.25 rps (73% of the original speed and 94% of the original spin)
3. Post ball-table impact (right after impact/before peak): speed 6.27 m/s, spin 46.30 rps (some of the spin was converted to speed)

2. HOWEVER, Newton, Decartes, Bernoulli, Euler, and Einstein all do not play TT. Otherwise they would have added the exception: due to special relativity, the spin speeds up the moment it hits your racket in an amount inversely proportional to your ITTF rating (the lower your rating, the more it spins faster, because the ball hates you).

Heisenberg did play TT and also e.g. Edward Teller https://www.webofstories.com/play/edward.teller/22
so we could simply take σx * σp >= h_bar/2 and define h_bar as the highest world rank

 

[Tony's Table Tennis]

I think trying to play against weaker spin is the wrong priority.

Priority number 1 should be reading the spin and the placement
2 is knowing how to play the incoming spin
3 the shot you want to play determines the contact point on where the ball travels
4 is based on the above 3 coming together, so the execution of the ball.

 

[Sherpa]

I find the longer you leave the time you contact the ball after it hits the table the more the ball has moved off lets say a straight line making it more difficult for you to return as it spins further away from you [sidespin serve]. I find it varies with the type of serve as well and also what you are trying to achieve with your shot

 

[StreamOfWater]

I am receiving conflicting information on this, some friends at the club told me it is off the bounce due to the ball briefly slowing down by the contact with the table before the law of physics make it resume its spinning and force, a friend told me that's why so many pro players like Truls just give the ball a quick zap to the ball the very instant it bounces.

Then some people say the ball loses spin exponentially the more I wait to hit it, I am talking serves receives here, so that would be around when the ball starts to go down?

Which one is it? Using the laws of physics and inertia, when am I LESS susceptible to the spin from a serve? When does the ball has less spin after a serve?

For the sake of this question, let's assume I am talking about a short/half long serve regular pendulum serve type of serve.

Any clear answer on this?

Pretty sure it's obvious to say that the longer the ball travels, the less spin it will have because energy doesn't come from anywhere. Racket gives the initially energy, everything after only slows it down. After a ball change, the ball loses spin incredibly quickly. Let's say you hit a good backspin serve that rolls back — by the time it hits opponent's side and starts rolling back, it barely has any spin

 

[canonFH]

I am assuming that you want to make the serve receive easier, that is why you're asking this question. If you're actually interested in the Physics of it, ignore what I'm writing.

If we ignore the Physics for a moment, and just go by what feels easier, you'll probably find it easier to receive using a push once the ball has reached its apex and is falling, and a topspin at the point where the ball is about to fall, or even when its rising. But you can't always react to the serve to reach the correct position at the correct time. So if you're particularly bad at receives, my advice is to pick a system (For example: topspin all long balls, and push all short balls) and master it. Then gradually incorporate variations.

The pros goals are different from yours and mine. They don't receive a particular way because its easy, or because the spin is less or whatever. Most of the time, their goal is to prevent the opponent from making a strong attack.

At my level, if I don't read the spin correctly, I can just chop it to the BH of the opponent. Even if its a bit high, I know my opponent won't kill the ball; even if he goes for it, he'll miss about 30% of the time.

Receiving at the bounce is a difficult thing to do. You have to know what is coming and where, and then be fast enough to reach there. Even then, your receive has to be at a particular angle, hold the bat at a particular stiffness, use a particular amount of force and then hope that you've read it correctly.

You have much more leeway when you're receiving late. You have more time to see the ball, and reach the correct position. You also have more contact time with the ball so you can also adjust a bit even after the ball touches the bat. If you don't know the spin, you can wait for the ball to completely fall and push it.

But the opponent also has more time to get into position and make a strong attack. Also, depending on the serve quality, late receives are difficult to keep short. Pros also receive late when they are having trouble reading the spin, most often with hook serves. A relatively recent UTT match of Kirill Gerassimenko vs Ankur Bhattacharjee comes to my mind. Umpires provided a lot of leeway to Ankur and Kirill couldn't read the serve thoughout the match.

 

[Tony's Table Tennis]

these kinds of statements are made by great coaches and are often useless. Issues with serve return are far less about spin susceptibility and far more about how easy it is to *read* spin and contact the ball at certain points in its trajectory to produce a certain effect.

I have to disagree with you here (agree on the front part).

I understand what you are saying, and how it is not applicable to lower level players, but the amount of spin and how much of the spin to override or to use/borrow, is part of service return and the useless things that you claim from great coaches does have a purpose and this all comes to the finer quality of the return. For example, BH flick, you can choose so many parts of that incoming position to flick the ball, and there is a meaning for each of the so called point of contact and we often have these conversions with players when working on service returns.

But now I'm going into territory not applicable for the forum but because it isn't applicable to the forum, it doesn't mean those statement from coaches are useless. It should be not applicable.

 

[igorponger]

SAVE MY TIME, PLEASE.

I make it an invariable rule for myself to not enter debates with non experts, nor to instruct the geeky guys. It is counterproductive time waste, anyway. Sorry.

You're welcome to leave questions to my PM. Веst regards.

 

[tzifos]

SAVE MY TIME, PLEASE.

I make it an invariable rule for myself to not enter debates with non experts, nor to instruct the geeky guys. It is counterproductive time waste, anyway. Sorry.

You're welcome to leave questions to my PM. Веst regards.

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I think that we have to distinguish the type of spins especially the up-spin by topspin and the down-spin like from a chop or push. The spin & speed change is quite different between these spins after the table bounce. For example when the ball has plenty of top-spin after the bound on the table its speed is greater and the opposite happens when the ball comes from a chop. The bounce height is also different; greater for down spin, less for up-spin.

 

[igorponger]

@ttarc

Hi, dear
Great findings of yours. Thanks. 👍
Btw, the test results will directly depend on the material and structure of the testing table, the surface COF foremost.
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Be happy all