grippy vs tacky?

it seems to me that tacky does not really increase the amount of spin; rather its purpose seems to be to suck power out of the ball, improving the short game.

seguso wrote: it seems to me that tacky does not really increase the amount of spin; rather its purpose seems to be to suck power out of the ball, improving the short game.

They way I know it, the tackiness is there to generate spin if you use the correct stroke. That's to compensate for a hard sponge (your typical hard Chinese sponges) which focuses on speed and hence less spin due to the less "dwell time" of a harder sponge compared to a euro/jap sponge.

To the original question - grippy and tacky both describe how much spin a rubber can impart on the ball. The difference is that:

grippy - produces spin due to the increased surface area that will "wrap" the ball when the ball sinks into the sponge

tacky - since Chinese sponges are harder, there will be less surface area that will "wrap" the ball and hence less spin. To compensate, they make the rubber tackier (more sticky)

Another note on the short game - actually..if you have a really tacky rubber, in PASSIVE strokes for the short game (i.e. blocks), you will notice that the incoming spin will have more dramatic effect (trajectory of bounce after hitting the rubber) and hence you need to use ACTIVE (or at least semi-active) strokes even in the short game.


Edited by davidwhang - 03/08/2013 at 11:50am

As a general rule making a topsheet more tacky will decrease elasticity and vice versa.
To compensate this tacky topsheets often have a bit thicker base for the topsheet and or firmer pips structure making them less supple in play. And also used with more firm sponges to avoid too much deformation of the topsheet in which case the lack of elasticity would be felt more.

Tackyness is not a real objektive meassure. Grippy topsheets also have some tack for celluloid but it,s just not enough to carry the weight of a ball.

From least grippy to extremely tacky it has a continuous increase for the so called frictional coefficient.

The frictional coefficient for static friction ( the ball dassumed not to slide to the rubber ) is more or less a constant given from the substances.
In this case the substances are celluloid and rubber with the cellluloid as a constant for all rubber offcourse.

So extremely tacky will have a higher frictional component then less tacky.

fc >/= Ff/Fn. This is the standard fysics equation for friction and normal force and fc can be bigger then 1 for this.

In words : the frictional component needs to be more or ecqual to the ratio between frictional force and the normal force both between ball and rubber to avoid slippage.

So higher frictional component means that for a given frictional force it needs less normal force between the rubber and the ball to avoid friction.  Or vice versa a higher frictional coefficient allows more tangential force excerted on the ball with the same normalforce.

Tackier means the ball can be brushed thinner and not tacky, less grippy needs a firmer contact for the same speed. That,s why tackyer rubbers are better in separating spin and speed ; at lesser normal force it will still allow an ecqually spinny ball.

In tabletennis practice decreasing the normal force is limited offcourse ; the ball will have to travel a certain distance and this needs a minimal normal force. But a shorter distance for short game will need less normal force for speed. More tacky rubbers usually have a more obvious advantage then for spin. For instance for a short return with a soft contact (thus lesser normal force) applying spin. A slow loop also can be executed more spinny.

But when the speed has to be increased with more "pressure", higher normal force, the normal force increases and won't limit the tangential force anymore in practice. So the advantage for spin becomes more or less neglectable or disappears completely. fc is not critical.

It can be confusing that pressure in tabletennis is often used as a term where for fysics the term normal force would be the adequate term. Pressure in the fysical sense (or contactsurface area) is not relevant for this. At least not part of this equation.

When an incoming ball has a lot of speed tacky topsheets and sponges that go with it most cases do tend to take kinetic energy from the ball. 
I also think it,s possible to transform this energy and with some energy from oneself use it for spin.
Technical skill and also being accustomed with equipment will determine to what degree this energy can be used or will be wasted.

Ps
Hope my English is somewhat understandable, it,s not my native language.



Edited by mercuur - 03/08/2013 at 5:55pm

Hitting into the sponge happens by virtue of the ball approaching the rubber. The more normal the blade face is to the approaching ball's path, the more penetration into the sponge. The player can increase the penetration further by hitting more and brushing less. Are these concepts perhaps the reason for the "hit then brush" theory?

Another faktor for spin with spongehardness could be that with harder sponge the forces/energy is concentrared on a smaller amount of pips involved.
When the topsheet is supple, wider spaced finer pips aso, the elasticity of the pips can be overstretched for best result. The harder sponge then makes the topsheet the limiting faktor for spin.
Making the sponge softer for such a topsheet involves a higher amount of pips in the action for spinstrokes and the elasticity for spin will feel and be stronger allowing more spin.
 
It has an optimum then, somewhere, for sponge hardness/softness depending on things as topsheettype and - strukture, technicque and also bladehardness/softness and incoming spin (when it comes to counterspin). The topsheet as weakest link in the rubber (chain) as a whole is in a way strenghtened by making another link (the sponge) less strong, easier to deform (relative to the blade) which is a known principle for many technical construktions.

Rubbers with a higher frictional coefficient can be used for high spin even with lower normal force and allows finer brushing.  Topsheet and sponge both have to be made stronger then to avoid that these become a limiting faktor for spin.  Otherwise the higher frictional coefficient would become useless.

...



Edited by mercuur - 03/11/2013 at 5:17am

seguso wrote: racquetsforsale wrote: Refreshing read. Thanks. Based on your explanation, for the same amount of spin, grippy rubbers require a firmer contact and therefore more penetration into the sponge than do tacky rubbers? This seems contrary to what I perceive as common perception and advice often given that Chinese rubbers require hitting more into the sponge than do their Euro/Jpn counterparts. It seems both tacky and grippy rubbers require hitting into the sponge, the former perhaps for more speed and the latter for spin. I think it is misleading to frame the problem as "chinese" versus "european", or as "tacky" vs "grippy". The correct framing is IMHO hard rubbers vs soft rubbers. Unless we are talking about brush loop, hard rubbers play the same for loops, whether or not they are tacky. For example, M1 plays the same as H3 boosted. With both rubbers, you don't get good spin unless you hit very hard. So no good spin in controlled loops, or blocks. I think Zhang Jike could play with M1 without changing his fh technique the slightest. (they say he uses a nontacky H3, by the way). Hardness is what matters.