Will it burn: Various TT Ball Halves Ignited

> The forces involved are much less that we typically see in even a low level match.

I recall a study of college level players (>>2k) showed ~20m/s top loop speeds. The ball drops significantly in speed (maybe ~1/3) at the other end of the table. This is for top end scenario, not typical club level shots. Most such fast shots taken are taken at near table level and don't clear the net by much, so the ~15deg angle isn't off by much.

Also, I'm pretty sure 2x speed isn't 4x force unless maybe you assume same stopping distance, and we can at least agree the ball is elastic and not magical.

> I see the errant bounces in my chopping drills against loops and forehand drives.

In your shots or their topspins? Can you experimentally/observationally control for their spin?

> All the more reason to think that a ball with a more consistent structure might produce a more consistent bounce. 

Except it doesn't at all empirically. Should we do a bounce test from 2x, 3x the height and see if it matters?

> Small cracks can have very minor (essentially not noticeable in play) affect on the bounce.

I'm talking about balls substantively cracked. Most of the time they're not landing on the crack yet don't bounce right at all since the structural integrity of the whole is affected.

> Players seem to be very much prejudiced by the sound that a ball makes.

I've mentioned this before somewhere as a possible source (I also think one of the main reason "bad" tables "bounce weird" even if they're uniformly rigid). Maybe it just sometimes sound, not actually bounce, different.

I think we'd have to do slow motion video studies of some ball flights to settle this.  While practicing chop against an over 70 hardbat player, his forehand drives frequently bounced well over my shoulder height - well more than 30cm and possibly over 50cm.  I'm pretty sure that high level players regularly loop well more than six inches above net height.

AgentHEX wrote: > > All the more reason to think that a ball with a more consistent structure might produce a more consistent bounce.  Except it doesn't at all empirically. Should we do a bounce test from 2x, 3x the height and see if it matters?

I am no engineer but the static bounce height strongly predicts whether people generally like to play with a plastic ball or not.  It is the single best predictor and I have actually have done some blind tests.  Of course, it is certainly possible that one could collect more sophisticated data with all sorts of variations in bounce tests and other stuff too.  The important thing is that the static bounce test suffices.  Probably other properties co-vary with this one and it doesn't mean that knowing all those other physical features of the ball are not in some way interesting.  If somebody wants to do it, great.  But the static bounce height is the single most obvious deficiency of Chinese seamed balls. Anybody can see it at their club or on any hard flat surface.  They are not at the ITTF standard coming in Jan. 2016, and it has a big effect on how Chinese seamed balls sometimes behave in live play (and why I do not plan to ever buy another one).  I also suspect the underlying reason may also explain their fragility too, but that is just guessing.

AgentHEX wrote: I'm only deducing from reproducible data for reasons you can be sympathetic to; otherwise the new ball might have more gears but less catapult and/or throw. Hopefully the direct hardness test (across both axis types) and its corresponding speed equivalency point can put your mind more at ease.

AgentHEX wrote: The base plastic materials like PVC these balls are made of tend to be significantly more elastic than celluloid so there's little reason for inherent low bounce, esp given other balls made of similar stuff. There's also zero evidence I've seen that they don't conform to 2016 bounce specs already. The difference to amended spec is only 3mm or ~1% anyway.

There may be little obvious reason but there must be something because they clearly bounce low.  I have no idea what they are made of, maybe you do.  Why do you think it is PVC?  I am not a materials expert so that is an honest question.  About the rest, if Debater's data are close to accurate, they will not pass Jan 2016 tests, but they might squeeze by on the low end under ITTF conditions.  Still, they are always lower than every celluloid ball and the other plastic balls too.  Always.  There are all sorts of not to fancy ways this can be shown.   The larger problem they face in the future, though, is that DHS/Jooola plastic are quite far from meeting weight specs.  I have not yet seen a single one that would pass!  My laboratory balances are very accurate (I don't normally use them for ping pong balls).  Personally I don't think the weight is why they suck.  It is the low bounce.

The reply above is to Jay.

> Why do you think it is PVC?  I am not a materials expert so that is an honest question. 

It's just an example, all such plastics I checked are better Young's modulus than celluloid. I arbitrarily picked PVC because I recall it has almost same density.

> About the rest, if Debater's data are close to accurate, they will not pass Jan 2016 tests,

Why not? Jay's test shows ~255mm for cell and Debater's test you mentioned was ~1cm lower (I didn't bother to check again). The cutoff is 240, the temp cuttoff is 237. Debater's actual results per se aren't accurate (but precise) because he bounced off wrong plate, but the relative delta is about right.

I think Joola cell is also DHS same as what Jay tested.

AgentHEX wrote: Hopefully you have a link since I don't know what you're saying. The DHS balls really don't have a bounce problem at least in ITTF's tests.

http://tabletennisengland.co.uk/wp-content/uploads/2013/04/Poly_Celluloid_Balls_Testing.pdf