Offensive Play and Spin
Rowden Fullen (2000)
When hitting the ball with an attacking shot the bat moves in a forward and/or upward direction. The forward motion projects the ball forward and the upward motion imparts topspin. The flatter the trajectory the faster the ball will leave the racket and the less topspin it will have. The ultimate is the flat hit which gives maximum speed and no spin. Topspin is the most important spin in table tennis because it gives a greater margin of error when hitting offensive strokes and without it we would not be able to hit the ball so hard when it is at or below net height. Due to the nature of the execution of the stroke in comparison with the drive (more lift) it is easy to use many more timing points and thus much more variation. What many players in the Western world especially women do not appreciate is the critical importance of timing in drive play. A flat hit will have very little margin for error and a slight miscalculation will cause the ball to go into the net or off the end of the table. However a topspin hit can be aimed well above the net and the topspin will cause the ball to dip down and still land on the table, thus giving a much greater margin for error.
Topspin is needed in attack because it gives the ball a downward-curving flight path while maintaining directional control. What is good about a downward-curving flight path? It is much more certain that the ball will hit the table because its final approach is nearer to the vertical instead of almost horizontal as in the flat drive. The gyroscopic effect of the spin gives strong directional control, thus more and more power can be fed into the stroke without greatly reducing the on-the-table accuracy.
An important point is that both backspin and topspin cause the ball to deviate in flight. Test this for yourself. In your own training hall loop the ball hard and long with much topspin — it will dip quickly to the floor during flight then after bouncing will spin forward and run on to the end of the hall. The backspin ball will veer upwards before dropping down, will run forward only a little, then will spin back towards you and can end up spinning back past you. Not only does the type of spin affect the ball in the air but it also affects the way the ball behaves after the bounce.
But why does spin cause the ball to deviate in flight and why do we sometimes have unusual, unpredictable effects after the bounce? This is in fact to do with the interaction of the spinning ball as it moves through the air against the flow of air molecules. (We have all felt air, when we stick our hand out of a car window moving at speed we can feel that air is rather more solid than we thought). As the ball moves through the air different areas of the surface are subject to lesser or greater resistance, the Magnus effect. With topspin the ball is forced down, with backspin conversely forced up. If we take a topspin ball for example, the fast moving area at the top of the ball opposes the air flow and we get resistance or high pressure. However at the bottom, the fast moving area of the surface moves with the air flow, the air molecules speed up and you get low pressure. As a result the ball is forced downwards. At the bounce the bottom of the heavily spinning ball is held by the table, topspin increases and the ball shoots forwards very quickly.
Once the ball has crossed the net some force is required to bring the ball down on to the table — gravity alone is not enough if the ball is travelling fast. This force is provided by topspin which causes the ball to dip. Therefore a hard hit must contain a lot of topspin to bring the ball down on to the table — the harder the hit the more topspin it must contain. Modern bats allow the ball to be hit very hard from below net height because they create sufficient topspin on the ball. This topspin also causes the ball to come off the table very quickly, shooting through fast and low after the bounce.
With the modern racket the characteristics of the sponge and rubber allow the bat to be swung in a different, flatter arc, giving more forward speed to the ball. Because of the spin produced, much more energy can be fed into the shot. In effect the ball sinks into the bat, is grabbed by it and as the bat is moving up and forward, the ball is projected upwards and forwards too. The surface of the rubber is very tacky so it grips the ball and imparts a great deal of topspin. It is this topspin which causes the ball to dip down on to the table. Another vital point is that for the same bat path, the faster the racket moves, the more spin it puts on the ball. A fast hit will contain more topspin than a slow hit. Most players, especially women, do not understand the importance of spin in hitting the ball hard. Very few women for example ever attempt to play with the same degree of closed racket angle as the men, so how can they hope to achieve the same level of spin as the men? It also means that the variety of topspin trajectories are often more limited in the women’s game. How much spin you produce is seen most readily when you play against long pimples and your hard hit comes back with very much more backspin than your slow hit.
Nowadays players have mentally absorbed the fact that topspin makes the ball shoot through fast after hitting the table. When they play against pimples they complain that the ball comes through much slower. Often players have problems coping with the flat hit with lesser topspin. The ball comes off the racket faster, therefore travels through the air faster, but comes off the table slower!
What many players fail to appreciate is that the ball will always come off the bat faster when it hits the bat at a perpendicular angle because the energy losses will be less. However fast and elastic, sponge cannot create energy, it can only minimize energy losses. With the sponge racket the grabbing and lifting effect enables the bat to be swung flatter to give more forward speed, but the flatter angle of attack means there are more energy losses due to a larger depression being made in the surface of the sponge. If the elasticity is increased, so that the ball springs off the racket more quickly, this will almost certainly reduce the lifting effect and the amount of topspin produced so there will be less ‘dip’ on to the other side of the table.
What players must understand too is that we should consider the relevance of speed over three different areas, speed off the racket, speed through the air and speed off the table. We should also consider how the different speeds are affected by how we play the stroke and then examine the trajectory of the ball. Will a loop ball which has a pronounced arc in trajectory reach the other end of the table more quickly than a flat hit which travels in a straight line? Obviously not unless there is a much greater difference in the power input.
We must also put a little thought into just how much effect the 40mm ball is going to have on our stroke play. 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 at around 1 – 2% slower through the air. If you just drop a big and a small ball from the same height, 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.
It is in the area of spin rather than that of speed that most players are going to notice a difference with the big ball. The critical factor is air resistance which will slow the larger ball more quickly, 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 reduce 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 still face much 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 with the air 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.
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 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 the women’s game. We must touch on science here again 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 as women don’t hit the ball as hard as men and usually play with a less closed bat angle, they will achieve proportionately less topspin effect than men on the power strokes such as the loop drive. Women will tend to suffer more with the big ball than men, those who do have a topspin game will be less effective because it will be more difficult for them to increase the spin element and thus some of the ‘on-the-table’ effect will be lost and with it a measure of control. 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 closer-to-table women players to cope with those who like to back away and topspin from a deeper position.