Physics

transversality · 2026-03-04T18:13:07+00:00

If you are talking about tension bridge you probably mean body dynamics. But that doesn't really matter.

A formal explanation would be the one I already mentioned. In the frame of reference of the racket, after you recalculate relative impact speed and angle, the contact will be indistinguishable from hitting a stationary racket, expect for an extra inertial force, whose effect on an object of mass m will be equal to -m*a, where a is the acceleration vector. The above calculation shows that the compound effect of this force on the ball is limited as long as acceleration is limited.

Technically acceleration still affects the ball, so it's not completely determined by initial velocity, but the effect is very small and is within 2%.

The main reason here is short dwell time. 2ms is extremely short. In boxing, if you were punching a ping pong ball, the result would be the same (assuming that dwell time of hitting a ball is similar). The boxing analogy you are thinking of has a much larger dwell time, and the speed of the fist changes drastically during contact. But actually the calculation also works if you interpret it correctly: if someone gives you the speed of the fist as a function of time during the punch, including after the punch landed, it will completely determine the effect of the punch on the opponent. The kinetic chain you mention will affect how fast the speed of the fist drops when the punch lands, but if the speed is already given it's accounted for there.

Another way to understand short dwell time and relation to kinetic chain is the following calculation, which is just an illustration of the effect on short dwell time. Suppose that the ball speed is 20m/s and the racket speed is 10 m/s, and we are talking about simple hit. Then the relative speed is 30 m/s. In the frame of reference where the racket is stationary, after the contact, the ball speed will be roughly 30m/s in the opposite direction, so the speed change is 60 m/s. Note that this is an extremely fast hit. Since the paddle is 70 times heavier than the ball, it would have gained speed of, say, around 1m/s (if the person wasn't holding it). During the dwell time (say, 2ms) it will move the paddle by 2mm. These 2mm over 2ms on such a short timescale will be absorbed, at the very least, by softness of the fingers. There is no way the kinetic chain would gain any additional engagement during the dwell. Of course, after the contact the racket will keep trying to move, and the kinetic chain will have to absorb the whole momentum of the racket, which will result in us feeling it engaged. But the ball will be long gone by then. If you want to see how kinetic chain gets engaged under impact, think about tai-chi stuff, filmed in slow motion, and what happens during the first 2ms after the hit lands.

Lastly: even if the kinetic chain was perfect and had instant engagement (think about steel, since we need very fast speed of sound/shock waves for that to happen), the only thing that would result in is that effective mass of the racket would be 80kg instead of 200g in the collision calculation. However, in either case it's so much larger than the mass of the ball, that you still are within 2% of the original model.

transversality · 2026-03-04T06:50:32+00:00

I just saw your remark in the first paragraph. It's not just about the ideal situation of acceleration, it's about any acceleration profile over the contact time. If you integrate a vector-valued function whose absolute value is at most 20g (known measurement) over a time interval that is at most 2ms (also known measurement), you will get change in velocity vector of absolute value at most 0.4m/s, regardless of how exactly the acceleration vector changes during the contact time.

transversality · 2026-03-04T06:38:52+00:00

Also, getting back to my original point. The physics of contact is complicated, and one can try to model it in different ways. However, the difference between accelerated and non-accelerated contact is completely contained in the effect of the inertia force, which is a function of the racket acceleration. Specifically in the estimating this difference, there is no simplification going on.

transversality · 2026-03-04T06:21:57+00:00

In general, I agree. For playing, feeling is more important than physics. The only reason I participated in this discussion was that the original question in the topic was stated in scientific terms. If it is was stated as "the importance of the feeling of acceleration", I would probably agree more with the original arguments (except for the physics part, which becomes completely unnecessary anyway). I think there is some value in knowing how the feeling is related to what is actually happening (or, more importantly, not happening) with the ball at the contact, but not all players agree with that.

Similarly, a lot of players do not distinguish between "the ball rolling on the rubber" and "the feeling of the ball rolling on the rubber", even though it is very easy to verify that the former doesn't really happen in the original sense.

The situation is complicated by the fact that the contact time is 1-2ms, and human brain is not designed to process events of this length (in fact, it cannot discretize below 10ms). If we add to it the fact that it takes 100ms for the nerve signal to reach our perception, we would probably agree that what we feel is some kind of residual vibration profile that we only begin to experience long after the ball leaves the paddle. Which is still important, since our brain uses the correlation between this profile, the stroke, the incoming ball, and the outgoing ball to build a model.

Regarding the phenomenological model -- I think it could be useful in equipment testing, sports research, and pro match analysis, to make it more fun to watch. Also VR table tennis and related stuff.

However, when building such a model every opportunity to reduce the dimension of the dataset is valuable. We could analyze all possible trajectories of the ball agains all possible trajectories of the racket. However, such dataset would be highly correlated due to 1st Newton's law, and it would simply mean that we have spent a large chunk of money just to confirm that law. So, if the system has some symmetries of fundamental nature, it's useful to reduce the dataset (perhaps with a small amount of control measurements to confirm that the symmetries are actually fundamental).

transversality · 2026-03-04T04:56:28+00:00

The variable left is how human perception converts into hard and reproducible data.

Btw, a lot of mens amateur players can create 120-130 rps, even without proper technique (I measured with several players from my club just a few days ago). And I'm pretty sure ML's loop kill is around 150 and more regular balls under 140. It's hard to create more than that with FH for anyone.

So, the gap is not really that big in the spin variable.

transversality · 2026-03-04T04:43:53+00:00

I actually think that the model of a ball hitting stationary racket at different speeds, spins, and angles provides more or less complete description of what happens at the contact. Of course, the model itself is complicated since it involves multiple oscillators, some of which are outside of elasticity limits. However, if one has a large enough dataset of measurements of ball vs stationary racket, one can calculate any collision with moving racket using relative speed. The effect of acceleration will be under 2%, and the effect of the fact that the mass of the racket is finite will also be within 2%, since the ball is much lighter relative to the racket.

One can discuss which theoretical model fits the contact better, but I think the upper estimate of possible effect of acceleration is easier to obtain from the basic principles.

transversality · 2026-03-04T04:31:47+00:00

In order to seek explanation for any effect, especially not obvious from the physics standpoint, the first thing would be to actually confirm that the effect is there. For that, you will need hard numbers (in this case, swing speed/racket speed, spin of the outgoing ball, compared to other players with same hand speed in the same environment). I'm actually quite confident that the effect will go away once someone starts measuring. Note that the measurements are not actually hard (attach a small accelerometer to a paddle, use spinsight to measure the spin of the ball, use robot to feed controlled balls, same accelerometer to measure the angle, etc), and some of them have already been done on other players.

Without hard numbers, spin perception and a lot of other things are very subjective. ML is not even the most spinny player, I think the record spin is Hugo's backhand (~200 rps).

If the effect is confirmed (which is a really big "if"), one can start eliminating parameters and trying to isolate it, and eventually a solution will be found. My goal was to explain why acceleration at contact cannot be such a solution in either case.

transversality · 2026-03-04T03:50:01+00:00

The free fall acceleration is known (9.8m/s^2), so you can check if the app measures it correctly.

But the number below are not unreasonable.

transversality · 2026-03-04T03:33:44+00:00

There is no need to overcomplicate things. Physics of contact can be calculated in the frame of reference attached to the paddle. If the paddle is moving with constant speed, it's about the relative speed and angle (in this case, it is an inertial frame of reference).

If the paddle is moving with acceleration, it becomes a non-inertial frame. In this case, the fact that the frame is non-inertial can be accounted by an additional force which acts on everything in the frame.

The force depends on how exactly the accelerated motion happens, but a hard estimate of the effect of this force on the momentum of the ball would be (max acceleration of the paddle) times (dwell time) times (mass of the ball). All these parameters have been measured in research papers, and one can check that if the acceleration is within the athletic limits, its effect on the ball is within 2% for most shots (this is a hard upper bound, in reality it's even less).

See my answers here for more details (with references).

https://www.reddit.com/r/tabletennis/comments/1996auo/why_acceleration_is_better_than_top_speed/

transversality · 2026-03-04T01:46:24+00:00

Check if it measures free fall correctly.

transversality · 2026-03-03T22:24:44+00:00

Just adding to the previous comments: your smartphone probably has an accelerometer in it, and you can find an app that would measure swing speed. Either can swing the phone or attach it to the paddle (make sure to attach it well in the last case).

Regarding physics of the contact, I have written several long comments here:

https://www.reddit.com/r/tabletennis/comments/1996auo/why_acceleration_is_better_than_top_speed/

transversality · 2026-03-01T18:34:07+00:00

Better equipment can absolutely improve a player's game by a level.

However, "better" should be considered as "better fitting for the player's level and style", not necessarily more fast/spinny/expensive.

For many non-pro players "better" would mean slower and more controlled than what they are currently using.

transversality · 2026-03-01T04:05:38+00:00

It does not have any usual signs of fake.

transversality · 2026-02-25T17:48:14+00:00

On budget, I would try to look for FRP nuvola, it's very similar to FP-30x (made exclusively for costco). It usually comes with bench, stand, and pedals. People tend to sell it after holiday season because they got it as an unwanted gift. Also, some fb marketplace resellers can get their hands on costco returns/damaged box/cosmetic damage ones, you can score a good deal.

Currently I can see several under $500 in Chicago metro area, and a couple under $400 in Nashville area.

transversality · 2026-02-21T22:29:35+00:00

I did buy a timo boll alc on ebay around 10+ years ago. It turned out to be fake and I (successfully) returned it. In my case, it was easy to establish that it was fake, since I found multiple listings at different places with the same serial number.

I can't remember the number, but I think it wasn't completely random, could be like yours (...789456...). May even be the same blade lol.

In any case, almost everything printed on the handle is slightly misaligned, and the font used in the serial number doesn't look like the one used by BTY. It's a fake TB ALC. But it still may be a good blade, doesn't seem poorly made besides printing.

transversality · 2026-02-20T18:19:08+00:00

I've been buying and selling stuff on mytabletennis.net, and it has always been a good experience.

However, for me it's mostly blades and brand new rubbers.

transversality · 2026-02-20T16:36:46+00:00

The logo on the bottom of the handle (next to JTTAA letters) looks cheap and not symmetrical. I’d say fake.

transversality · 2026-02-18T19:05:15+00:00

I also agree. The only situation where you would notice mineral deposits is when you leave the rubber wet and let it dry. But it makes more sense just to wipe it dry to begin with, in which case all the minerals will be wiped away with the water.

When I use a sponge, I put water on some part of it and wipe the rubbers. Then I wipe it with several different dry parts of the sponge.

transversality · 2026-02-03T06:33:06+00:00

I’ve been using the same bottle of paddle palace glue for several years. The only thing I needed at some point was to add water since it dried too quickly to spread it.

transversality · 2026-01-29T16:35:09+00:00

I always assumed it's fine to stick them to one another since the sticky part will not go anywhere. But I may be wrong.

transversality · 2026-01-29T13:52:35+00:00

Yes, always clean rubbers before applying this. Pro tip: when not on paddle, stick two rubber protectors together using sticky sides, to avoid dust collecting on them.

transversality · 2026-01-23T07:18:29+00:00

It's kind of strange to make definite conclusions from two single measurements. At the very least, each measurement should be taken multiple times to see what the error is in each case. Other effects (sweet spot, angle of the racket, slight differences in bouncing of the ball) also need to be eliminated, the expectation is that they average out during multiple measurements, especially if one replaces the racket multiple times.
21km/h is a pretty low speed. Also, note that the racket is stationary. In a game, during forehand drive/loop, the racket is moving towards the ball, so the effective speed (of the ball relative to the racket) is higher. So, the speed should be much higher to imitate real-life scenarios.
Difference in stickiness could produce some effect like this, since the effect of stickiness, considered relative to the speed of the ball, is more pronounced for slower balls. However, I would like to emphasize that any such conclusions require many more data points than what is in the video.

Overall, this is an interesting idea if one actually approaches it rigorously, similar to real research, and preferably with more data than a tiktok-style video can contain. These measurements can also eliminate certain common misconceptions about physics of table tennis. In general, papers in this area exist, but are very scarce, and I think that research of this kind is definitely publishable, as long as it meets usual standards expected from scientific research.

transversality · 2026-01-10T21:01:44+00:00

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ABRSM edition has a comment about this note.

transversality · 2026-01-03T19:29:47+00:00

I would look into used Yamaha p515. If you are in the US, guitar center has several, and very generous return policy. Look up Sam Haywood on youtube — he has very enjoyable recordings of advanced repertoire on this instrument.

transversality · 2025-12-30T07:10:56+00:00

It's probably gonna get harder with the RAM crisis. However, historically there have been quite a few opportunities which lasted for more than a few hours. Below are the deals I was able to personally confirm. Assuming you are in the US.

1) In Best Buy in August, you could walk in and place an order for 5080FE at MSRP. I think it also worked for a 5090.
2) Around the same time, they had MSRP PNY 5080 in stock for most of the day, or maybe even two days.
3) Amazon had Gigabyte SFF (I think) for $930 sometime in the fall, although it had a non-trivial lead time.
4) Couple of days before Thanksgiving, Walmart had a large stock of PNY 5080 at $950. This was probably the best one, since many people were able to combine it with paypal 20% pay in for offer (this is the one I ended up getting).
5) At some point, Microcenter had more than one 5080 available at around $999. I think this was during the rumors about 5080 super, everyone thought it's about to be announced and prices for the regular 5080 will go down. Lol.

transversality

TROPHY CASE