What is going on with Spin?
There is never a time in which a player wants to make in the cue ball, which means that this is a bad shot. Why did this happen? Conservation of momentum says that all of the cue ball's energy should be transferred into the yellow ball and the cue ball should then be at rest. Think about what happened.

Here is an aerial view of a second shot taken from the exact same place. Notice how the cue ball stays on the table.

 

If your answer is that I used spin differently, you are wrong! In both cases I used follow.  You can see in the gif that the cue ball rebounds, but then spins forward. The ball stays on the table due to the location the yellow ball is struck. I do not hit it squarely enough for the cue ball to directly follow it in.


Any skilled player knows that spin is an important part of billiards. This is usually referred to as English if it is side spin. If it is vertical spin, it is called draw or follow depending on the direction the ball goes after the shot. Follow is accomplished by hitting the cue ball near the top. It is an applied forward spin. As you can now guess, draw can be accomplished by hitting the ball near the bottom, which applies backspin. English is then accomplished by hitting the side of the cue ball, as shown in the following picture.


Taken from http://billiards.colostate.edu/physics/Alciatore_SCIAM_article_posted_version.pdf

Due to friction, half of the radius is the maximum spin that can be achieved without the cue ball slipping. For a detailed math and physics analysis of why this is the case, see http://billiards.colostate.edu/technical_proofs/TP_2-1.pdf .

Once the ball has been struck, we have what we have already discussed, linear momentum. If the ball was struck to have spin, we have a second momentum called rotational momentum. This is defined as    L = Iw where L is the rotational momentum, I is the Inertia, and w is the angular velocity. Inertia is an objects tendency to resist a change is motion. This is a value that depends on shape and mass. Angular velocity is the rate of change of angular displacement. It is not very practical to do a problem on something like this because angular velocity is not something that can be easily determined as the ball is struck. The only thing pool players need to know is that spin can be applied to make the cue ball land where you want it to go, or aid in making a difficult shot. The following video link gives an example of applying English to make a shot. http://billiards.colostate.edu/normal_videos/NV4-17.htm. I would show you a gif of myself doing this, but it is not something I can do. English should really only be used by expert pool players. Now you know how spin works! Play smart pool players

 
      
Next Page: Sources
Title Page