Do shots with backspin or topspin throw as much as shots with stun?
Stun shots exhibit the most cut-induced throw (see “Throw – Part II: results” – BD, September, 2006) and spin-induced throw (see “Throw – Part IV: spin-induced throw” – BD, November, 2006). For more information, see the maximum throw resource page. Draw and follow shots at the same speed result in up to 75% less throw for cut angles up to about 30° (see “Throw – Part III: follow and draw effects” – BD, October, 2006). Throw is a result of horizontal rubbing motion caused by friction between the CB and OB during contact. When a stunned CB hits the OB at an angle, the rubbing motion is completely horizontal, creating maximum throw. When there is top or bottom spin, the rubbing motion is less horizontal, creating less horizontal throw. Also, for a given shot speed, the relative speed between the ball surfaces during impact is faster when there is top or bottom spin, which reduces the amount of friction (for more info, see maximum throw). However, as described in one of the follow-up questions below, these effects are less at larger cut angles.
In comparing throw of draw and follow shots at the same CB speed at OB contact, the amount of throw is the same if the amount of backspin is the same as the amount of topspin. For more information, see “Throw – Part III: follow and draw effects” (BD, October, 2006) and Bob Jewett’s May ’06 article. However, because bottom spin wears off due to “drag” action, many draw shots will have less spin, and more throw, than typical follow shots (because most follow shots, especially those at slower speed, will have complete forward roll). The drag action of a draw shot also slows the CB on the way to the OB which also results in more throw. On the other hand, typical draw shots are often hit with more speed than typical follow shots, and there is less throw with faster CB speed at OB impact.
Now, when the CB is far from the OB, it is difficult (or impossible) to create slow-speed stun. If this is the case, a slow follow shot might create more throw than a stun shot, which need to be at a much faster speed which results in less throw (see throw speed effects).
One advantage of draw shots compared to follow shots is the backspin rubbing of CB on the cloth tends to wipe chalk marks off the CB (especially the new mark from a straight draw shot). This can reduce chances for cling/skid/kick on future shots.
Object ball (OB) swerve has a slight effect on throw with topspin and bottom spin. A follow shot will have slight OB swerve in the throw direction, effectively increasing the effective throw a tiny amount (more when there is cling/skid/kick), but the effect is very small (see the end of TP A.24 for example numbers). For all practical purposes, follow and draw shots with equal amounts of spin and speed at OB contact throw the same amount.
Do I need to aim follow and draw shots differently than stun shots?
Yes. As mentioned above, stun shots (with no top or bottom spin) involve the most throw, especially at slower speeds close to a 1/2-ball hit. With a cut shot, cut-induced throw (CIT) makes the effective cut angle smaller, so you need to aim to overcut the ball slightly (unless using outside english). For many shots, one doesn’t need to adjust for throw, especially with short and fast draw or follow shots on tables with generous pockets. However, on a tight table, and with longer shots, one must adjust aim for throw and be aware of the various throw effects. This is especially true for softer-speed shots with very little top or bottom spin (i.e., close to stun).
If you are comparing a draw or follow shot to a stun shot with the same CB speed at OB impact, because top and bottom spin decrease the amount of throw, the effective cut angle will be slightly greater with draw or follow. So if comparing to a stun shot, you can aim a draw or follow shot slightly fuller. However, as mentioned above, drag and shot speed are also factors.
Why do stun, follow, and draw shots create radically different amounts of throw at small to medium cut angles and similar (but smaller) amounts of throw at large cut angles?
The reason why top and bottom spin make less difference at larger cut angles is that sliding motion between the CB and OB is mostly horizontal at the larger angles. Imagine a CB spinning in place with topspin in contact with an OB ball. If the CB is in front of the OB (as with a full-ball hit), the CB is rubbing straight down on the OB. Now, with the CB still spinning, move it around the OB (while keeping the spin direction the same) simulating different cut angles. When the CB is on the side of the OB (as with a 90° cut), the spin creates no rub at all at the point of contact between the balls. The amount of downward rub changes gradually with the cut angle. It is larger for a small cut angle, and smaller for a large cut angle. That is why stun, follow, and draw shots create similar amounts of throw at larger cut angles.
Dr. Dave keeps this site commercial free, with no ads. If you appreciate the free resources, please consider making a one-time or monthly donation to show your support: