One of the coolest and most useful shots to use when in a jam, the bank shot is a shot worth mastering which takes both skill and knowledge to execute. For any beginner looking to learn about banking, check out the banking lesson to learn the basics of aiming a bank shot. This lesson will cover some of the variables that come into play when banking balls.
Once you have the basics of bank shots down, you’re going to want to know about a few variables that affect a bank shots trajectory. Since pool has a lot to do with physics, theory and geometry only help so much to visualize a bank shots path. You need to use experience and feel to properly adjust for all the variables at the table. The three main factors you need to be aware of are speed, spin, and cut angle.
The most important, and the most noticeable factor for changing bank shots trajectory is speed. The speed of the bank shot is hit is noteworthy because the harder you hit a ball into the rail the more that rail compresses. Rails are made from rubber and rubber is a springy material which makes it flex and move when struck. This is exactly what happens when a bank shot is hit hard, the rail gets pushed in farther than it normally does, and it decreases the angle that the bank shot comes out.
Conversely, if you hit a bank shot soft it will go wider than on a typical bank shot. Because the rail is compressed less at slow speeds it tends to have a wider angle. In the demonstration below you can see that even though both shots are aimed in the exact same direction there are drastically different results depending on the speed of the cue ball.
These examples used 3 balls lined up in a row to show that the aim of the bank didn’t change and spin isn’t throwing the balls in another trajectory.
Whenever you use spin on the cue ball to hit an object ball, the object ball always takes some of the cue balls spin and goes in the opposite direction. When you put right spin on the cue ball the object ball will have left spin when they hit because the friction between the two balls is enough to impart the spin from the cue ball.
This means that on bank shots, if you use spin on the cue ball you can change the path of the object ball off the rail since it will have some spin. When you use inside english, this puts opposite spin on the object ball which shortens its path and when you use outside english on the cue ball the path of the bank shot widens. This can be helpful when you can’t see the entire ball you’re trying to bank and either need to shorten or lengthen the shot to make it.
Along with using spin on the cue ball to change trajectory, cut bank shots also impart spin on the object ball. Therefore, for banks shots that are not straight on, you may need to cut the object ball more or less to make it than you think. Reverse cutting bank shots usually means you need to cut them more to make them whereas cutting across the object ball requires less of a cut shot.