The 40mm Ball

Rowden Fullen (2000)

The 40mm ball has a larger surface area so it will suffer more air resistance, which will tend to slow it down in flight. This however is offset by the fact that the ball is heavier and a heavier ball does not suffer so much retardation as a light one. If the weight is increased pro-rata with the size, then the two cancel each other out and the two balls will travel at the same speed through the air. The I.T.T.F. specification for the big ball is not quite a pro-rata increase which will mean that it will travel around 2.5% slower. To achieve the required weight the material for the big ball will need to be slightly thinner. Perhaps the I.T.T.F. recognized that it could be difficult to produce a ball that was consistently hard, for in the quality assurance tests they specified a median value which is slightly higher. Balls meeting this value will travel only about 1.5% slower. They further specified a maximum value which gives a pro-rata increase, meaning that the two balls would travel at the same speed!

Without accurate scientific testing (this would of course mean testing in the way in which table tennis strokes are played, where the racket contacts the ball usually at an angle and propels the ball forward) it remains to be seen what can be achieved practically but it would appear that the big ball will travel around 1 – 2% slower through the air. If you just drop a big and a small ball, they will both reach the ground at the same time but the big ball will not bounce up so high. Therefore it is in the reaction off the bat and off the table where any significant reduction in speed is likely to occur. Any specific reduction is not easy to assess because practically balls do not meet the table or the racket perpendicularly and even more importantly contain spin, which affects speed through the air and after the bounce. In some of the initial tests done in the research centre in Ottawa, they found that the harder the hit, the less difference there was between the speed of the big and small ball! Perhaps a really hard hit and the big ball will travel faster than the small one! Indications at the moment are that speed at the fast end of the game has not been affected very much but that speed at the slow end is rather slower.

Most players agree that the ball is more visible, slows down more quickly and tends to dip at the end of its trajectory. It also drops down to floor level rather more rapidly and doesn’t ‘carry’ so far after bouncing as the small ball did, especially with a lesser power input. As far as the ball coming off the racket is concerned, the sponge and rubber combination we use cannot create energy, it can only minimize energy losses. The ball will deform as will the racket surface — such deformation represents a loss of energy and the rebound speed of the ball (other aspects being equal) will always be less than the impact speed. The bigger ball with a larger surface area and the racket surface will both deform more, leading to higher energy losses. A similar situation will occur when the larger ball hits the table, there will be a little more deformation, a little higher energy loss.

It is in the area of spin rather than that of speed where most players are going to notice a difference with the big ball. The critical factor is air resistance which will slow the larger ball quicker, accelerating the dissipation of spin and causing it to ‘dip’ more rapidly under topspin conditions. The speed of revolution (spin) will be in inverse proportion to the size of the ball. The larger ball will clearly spin slower and less and since any point on the surface will travel further to complete a revolution, the spin will decrease quicker due to air resistance. However there is also the possibility that because of the larger surface area it is feasible that more friction can be transmitted to the larger ball, so that in service, very thin contact or over the table shots the opponent who stays close may face more spin! This is of course an equally valid argument with the hard hit ball but if the opponent takes this at a deeper position much of the spin will have dissipated.

A particularly important aspect is what happens after the ball hits the table. Spin is converted into forward or backward momentum. Topspin will add to the speed of the shot after the ball has bounced — the bottom of the ball stops but the top shoots forward increasing the topspin. With the larger ball where we have a larger surface area contact this will tend to dissipate the spin, but at the same time the bottom of the ball should be gripped more on contact thus increasing the topspin effect after the bounce. Which will predominate? Players seem to agree that the big ball dips more both before hitting the table and after the bounce.

Only months after the introduction of the 40mm ball many manufacturers were already producing quicker or oversize blades and faster glues. One of the answers is obviously to increase the power input so we have more spin and speed off the racket and thus to restore the status quo. But is this really the smart thing to do? Surely we the innovative players should be thinking of how to turn any new situation to our advantage not to restore things to what they were? Do we really want to end up slugging it out topspin to topspin two and a half metres back from the table till one or other player tires? If the ball drops rather more quickly, especially with spin and if there’s more effect with the slower shots, perhaps we should look into these aspects rather more — spin and variation rather than power!

It is perhaps also of interest to think a little of the difference in the power element between the men’s and women’s game. We must touch on science here for a brief moment — we know that a modern ‘sandwich’ rubber racket can be swung in a much flatter plane than the old ‘hard’ bat, thus giving the ball more forward speed. The harder the ball is hit with this type of stroke, the more topspin it will contain. The sponge does much of the work in lifting the ball over the net and the spin in bringing it down on the other side of the table. However women don’t hit the ball as hard as men and will therefore achieve less topspin effect than men on the power strokes such as the loop drive. At the very highest levels in the women’s game those players who use the power strokes are going to achieve less spin through the air, less ‘dip’ on to the table and less speed off the table after the bounce. It should therefore be rather easier for the close-to-table women players to cope with those who like to back away and topspin from a deeper position.

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