Understanding that the cue-ball will deflect off at a 90 degree angle after making contact with the object ball is a very important concept to understand when learning cue-ball positioning.
You will use 2 object balls and the cue-ball for this drill.
Place one object ball near a pocket, any pocket. The other put randomly on the table.
You are given ball in hand. Place the cue-ball in a location where you will be able to make both balls. You should hit the cue-ball center in order to judge the delflection at a 90 degree angle. The cue-ball needs to still be sliding when it hits the first object ball.
It is important to remember that at longer distances away from the first object ball the cue-ball must be struck harder. If the cue-ball isn’t sliding, but instead has generated some foward roll, it will not come off the object ball at 90 degrees. The cue-ball will drift foward and deflect at an angle greater than 90 degrees.