Billiards (aka pool) is a common sport in which the competitors try to knock their balls (either stripes or solids) into cups around the outside of the table. They use a Pool Cue to hit the Cue ball into other balls which will cause them to move in certain directions and ultimately into the cup. This sport is different than others because it SCREAMS physics: collisions, angels of incidence and reflection, friction and many other concepts are what this sport revolves around. First off, when the cue ball collides with other balls (assuming perfectly elastic collisions) momentum is conserved. This comes into play when the competitor is judging the amount of speed necessary to complete a shot. The more speed the cue ball has at impact will mean that the speed of the ball it hits will also increase. Another shot to perfect in billiards with the bounce shot. More often than not, the balls are not perfectly lined up to get the best shot possible.....so, the competitor needs to utilize the walls and bounce the ball off the wall in order to hit the target ball. When judging the angle to bounce the ball at, the competition must know that what ever angle the ball hits the wall with is the same angle it will bounce off with (angle of incidence=angle of reflection). Finally, frictions plays a very important role in the collision of the cue stick and the cue ball. Professional pool players put spin on the cue ball in order to make it do different things to give them an advantage. Often, the player will put chalk of the end of the pool cue to increase the friction between the sick and the ball which will increase the amount of spin on the ball and with more spin comes better results. So next time you play pool, think of the physics behind it.