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# Billiards Simulation/Game

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Hi all, I''m attempting to write a billiards game. Because the game is just something to do in my spare time, my goal is to use a fairly accurate representation of the physics involved. I took a physics course a couple of years ago, but I guess I didn''t understand this stuff as well as I thought :-\ I''ve searched through the forums for more information, but I''ve been having a hard time getting my head around it. If I throw out too many questions or too much stuff in general, just let me know, and I can separate some of it into another post. First let me explain how I think this should work, so that we can make sure my concepts are right. When the cue stick strikes the cue ball it imparts an impulse (? or force?) onto the cue ball, which changes the cue ball''s velocity (assume it strikes exactly at the center of ball). Ok, here is where I start to get confused. As I understand it, if the velocity of cue ball is high enough, it will overcome static friction, and begin to slide across the table. Once that happens, dynamic friction applies a force that (has the effect of) slowing down the ball. In a fairly short period of time, the velocity drops to a point where it cannot overcome the force of dynamic friction. However, the ball still has some momentum. Now does this cause the force of dynamic friction to apply a torque to the ball? If so, this is what starts the rolling of the ball. I''ll stop here for now. Ok, that could very well be incorrect in part or in whole. If it is right, then my questions are: I have seen on this forum (and in other resources) that frictional force is F = mu*N where N is the normal force and mu is the frictional coefficient (different for static and dynamic). As I understand it, gravity applies a force to the ball and the table applies a force back up, which is the normal force. So assuming that, our frictional force will be in the direction of the normal force... but I thought frictional force was applied in the direction opposite of motion? If it isn''t, then what exactly causes the ball to slow? (I think understand the link to the normal though... the stronger the normal force, the stronger the two objects are being pushed towards each other, and thus friction should be stronger.) Another question relates to once the ball starts rolling. Is it dynamic or static friction that is in play here? I don''t think it''s dynamic, as the ball isn''t sliding across the table. But I''m not sure what to do with static friction. Or am I thinking wrong and the frictional force is actually applying a torque in the direction opposite that of the ball rolling? Sorry for so many questions. I have googled and found some good information, but I am still struggling, so I''m hoping that some dialogue will help me. Thank you to whoever can and will help me

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