Why is CIT less at faster speed and SIT less with lots of sidespin?
The direction of throw depends on the direction of the rubbing. Maximum throw occurs with just the right amount of rubbing speed. Less rubbing gives less throw, and faster rubbing also gives less throw:
Per NV B.86 and “Throw – Part II: results” (BD, September, 2006), cut-induced throw (CIT) is actually independent of speed (i.e., the throw is the same at all speeds) at cut angles below about 20°. At larger cut angles (i.e., thinner hits), the amount of CIT is significantly larger for slower speed shots as compared to faster speed shots. For more info, see “Throw – Part II: results” (BD, September, 2006) and Ball Motion Properties in Stun and Follow Shots.
Spin-induced throw (SIT) with a straight shots is also independent of speed for small amounts of sidespin. See “Throw – Part V: SIT speed effects” (BD, December, 2006). Per Diagram 1 in the article, below about 25% spin, speed has no effect on the amount of SIT. For more information, see: HSV B.18 – spin-induced throw speed and english effects. Per NV B.86 and “Throw – Part V: SIT speed effects” (BD, December, 2006), SIT is largest for a slow stun shot with about 50% of maximum sidespin (for a straight shot). SIT is less at larger amounts of spin (greater than about 50% of maximum sidespin). For how maximum SIT varies with shot speed and cut angle, see TP B.25 – Percentage Sidespin Required for Maximum SIT at Any Cut Angle.
The reason why CIT is less at faster speeds and inside spin at larger cut angles and SIT is less with more sidespin is: friction is less at faster sliding speeds between the ball surfaces. With more cut angle and speed or with an amount of sidespin very different from the gearing amount, the CB slides along the OB with faster relative speed during contact, producing less throwing force. One possible reason for this is that the air compressed between the balls during contact doesn’t get out of the way as easily with a faster relative surface speed. Also, maybe with faster relative surface speed, the asperities (small but rough features) on the surfaces don’t interact, catch, or lock as easily since they are hitting, flexing, and vibrating more dynamically. Here’s an example where throw is less with inside spin as a result of this effect:
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