Topspin and Backspin
Rowden Fullen (1990’s)
With the many varying rubbers on the market it is not always possible to rely on the stroke action. (e.g. a push against backspin may be backspin, float or topspin!).
Try to read the spin by:
- flight (the trademark on the ball). Watch the ball 5 to 8 centimetres before it hits the table on your side.
- bounce (what the ball does after hitting the table).
Explain with diagrams, the turbulence and high pressure on the top side of the ball, the low pressure on the bottom side. Air pressure forces the ball downwards. The topspin ball is faster through the air and dips and shoots forward after bouncing. The incoming angle is greater than the outgoing angle.
The backspin ball has low pressure on the top side, turbulence and high pressure below. Air pressure forces the ball upwards. The backspin ball is slower through the air, carries a little longer in flight and kicks up after bouncing. The incoming angle is less than the outgoing.
Points to consider — Your opponent’s topspin spins towards you, his backspin away from you. When your opponent plays with your topspin the ball is returned with backspin, when he plays against your topspin he returns the ball with his topspin, (the opponent reverses the spin). However this may not apply if he or she is using long pimple or anti-loop where he or she cannot or can only partially reverse the spin.
Let us look a little at spin, what it is and how it affects the ball, because we need to know a little about the basics before we can cope with playing against different rubber combinations. Most players and coaches will be aware of what is known in physics as the Magnus effect. In many countries in Europe it is taught in the first coaching stage on trainers’ courses. The 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.
- No spin — same angle in and out. (physics, angle of incidence = angle of reflection.) This rarely happens in table tennis, test for yourself by throwing a no-spin ball forward, the ball acquires topspin after bouncing because the bottom of the ball is held momentarily by the floor and the top moves forward. (If a topspin ball hits the net, the bottom of the ball is held and even more topspin is created.)
- Topspin has a smaller angle after the bounce and the ball shoots forward low and fast. However if you have a high, very slow loop with much spin, because the main impetus is down the ball will often kick up a little, then drop down very quickly. This is why this type of loop is very useful against defence players.
- Backspin has the bigger angle after the bounce, the ball slows and kicks up sometimes quite sharply. Why many players have problems against backspin is that they don’t understand this slowing-down effect, that the ball doesn’t come to them. They must move forward, lower the centre of gravity and get under the ball.
Topspin is of vital importance in modern table tennis. Without topspin it would be quite impossible to hit the ball as hard as we would like to. When we for example hit a ball which is below net height gravity is not enough to bring the ball down on the other side of the table, especially if it is travelling fast. Another force is required and this is provided by topspin which causes the ball to dip sharply downwards. Thus the harder we hit, the more topspin we need to bring the ball down on the other side of the table. Our modern reverse rubbers give us great help in hitting the ball very hard from below net height, because they are capable of imparting very much topspin. This has an additional advantage in that the ball shoots off the table very fast 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. Topspin forces the ball down, backspin conversely forces it 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 we get low pressure. As a result the ball is forced downwards. At the bounce the bottom of the heavily spinning ball is held, topspin increases and the ball shoots forwards very quickly.
Sometimes the ball behaves in a different way and not as the laws tell us it should. In fact at times it can behave exactly the opposite to what we are led to believe – a topspin can jump up and a chop can skid low under certain circumstances. This is because of what occurs in the last 20 – 25 centimetres of flight, just before the ball actually strikes the table, (this is also a time when few if any players watch the ball.) A skidding chop occurs when a ball comes through low with very much backspin, (often for example when a defender takes the ball early when it is still rising) — the spin tries to make the ball rise and kick up during the last few centimetres of its travel and after the bounce, but it hits the table with a shallower angle than usual and also at a faster speed and a lower trajectory. What ends up happening is that the ball skids through quite fast and low after bouncing. Equally a slow loop with a great deal of topspin and a high arc, will dip sharply at the end of its flight and hit the table at a steeper angle than normal. Its downward velocity is increased and it has a higher impact speed so often the ball will kick steeply upwards after bouncing before dropping down sharply. Tactically this can be extremely useful if you can loop either very short or very long on the opponent’s side of the table.