From a pool player's perspective, it just happens. Lol. From a physics perspective, it's a friction-time thing.
The actual time that elapses during the collision is called the
impulse. Naturally it's a tiny amount of time, measured in milliseconds. If you checked out the BU link, you probably noticed Dr. Dave's test results show less throw when the CB is shot hard versus soft. This is because a faster CB-OB collision creates a smaller impulse (contact time at the moment of collision). The softer shot has a slightly higher impulse during collision. Friction occurs during this time, so more time equals more friction, which equals more throw. Different angles produce different amounts of friction/impulse times as the CB's momentum transfers to the OB.
Here's where the stun shot comes in.... If the CB is rolling, or spinning forward or backward when it strikes the OB, it has a perimeter velocity during collision. The friction is reduced because the point of contact between the balls isn't stationary, the perimeter (outer surface) of the CB is moving across the contact point on the OB. A sliding CB (stun shot) results in a stationary contact point between the balls for the duration of the collision. I'd say it's sort of like the old box on a ramp: Think of a heavy box on a steep ramp. The friction between the box and the ramp is greater when the box is stationary. It takes an effort to get the box moving, but once you get it moving the friction decreases with the momentum of the sliding box, and it slides on down the ramp with minimal effort. Maybe that's not a good example.
