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Billiards: transmitting side

  1. Feb 19, 2009 #1
    Hello everyone,

    this seems to be my very first post on this forum. To some it might not seem like a reason enough for registering, but I do have a question bugging me and where better to ask than here.

    So in billiards games, taking in consideration an approximated fastest shot of 30 mph which is 50kmh, and a very fine ball surface and rotational energy. Do you think it would be possible to transmit adequate amount of this rotational energy from the cueball onto the object ball, so that the object ball would gain a wider/narrower rebound angle?

    Thanks to anyone who takes some time to answer my question
  2. jcsd
  3. Feb 19, 2009 #2


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    Zero spin at the point of contact results in a 90 degree angle between cue ball and object ball (or cue ball stopped after collision). Topspin results in less than 90 degree angle, backspin results in greater than 90 degrees.

    Collisions between billiard balls involve very high forces, so even though the coefficient of friction is low, some rotational energy is exchanged during a collision. There is also friction between felt and billiard ball, but the force is just the weight of the balll unless the ball bounces.
  4. Feb 20, 2009 #3
    basically, I'm not disputing that cueball does transmit side onto an object ball, but considering the conditions (materials and size of the contact surface), can the transmitted rotational kinetic energy be so substantial that the change in object ball's trajectory would be significant enough to effect the game?
  5. Feb 20, 2009 #4


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    There is something in my town called the 'Danny Cut'. Back when I was first learning to play, I realized that my cutting was far in excess of anything that an opponent expected. Can't bank worth a damn, but I've managed a couple of times to cut an object ball over 90º. The way that I did it was to put all possible opposite spin on the cueball, and aim for the paint on the edge of the object ball. There's a masse effect involved, as nearly as I can determine. Whatever the science behind it, it earned me my first trip to the world finals in Vegas.
  6. Feb 22, 2009 #5
    I am not exactly sure what you are asking but I know a bit about pool so maybe this will answer your question. The short answer is that in playing the game you can ignore the spin that is imparted to a ball from another spinning ball if there is any (at least I have never noticed any but I will check this next time I play since it's an interesting question). The contact area and time is extremely small so I think that if the effect is there it is so small it can be ignored. Look at what you have to do to the cue tip just to make it impart spin on the cue ball. It has to be rough and covered with chalk or it won't spin the cue ball at all and a cue tip is much softer than a ball.

    The cueball can pick up spin in a few ways. You can give it any spin with the cue stick. Any ball will pick up top spin from the felt eventually. If a ball is hit hard and fast it can take quite a distance before it will pick up top spin from the felt, slow and it will start to top spin (roll) almost right away. Although this spin is actually just rolling it becomes important when the ball changes direction. It has to lose that spin and acquire the top spin of the new direction. Balls will also pick up side spin from a bank. The smaller the angle of incidence the more side spin they will get. This is because the ball has a much larger contact area for a much longer time with a bank than it does hitting another ball.

    Angle of incidence equals angle of reflection except in pool. The angle of reflection is almost never the angle of incidence. Partly because of acquired rolling spin or imparted spin, partly because rubber doesn't return 100% of the energy put in. With large angles of incidence the angle of reflection is usually more. With shallow angles of incidence the angle of reflection is usually less than the angle of incidence.

    The most important thing to know about pool is that the striking ball always tends to move off at a tangent from the point of contact while the ball that is struck by another ball moves directly away from the point of contact, perpendicular to the tangent. This is generally only modified by the spin on the striking ball. The struck ball can be pushed a little when hit hard at a good angle. Understanding the principle of the tangent you will always know not only where the ball you hit with the cue ball will go but where the cue ball will go after it hits a ball.
  7. Feb 22, 2009 #6
    You would have to masse it around the ball to get over 90°, it would be impossible otherwise.
  8. Feb 24, 2009 #7

    Its good to join your discussion here....

    Many players have a good cue action but seem to be afraid of cueing.When you are ready to follow through, you should attempt to push the cue through the cueball with a fluent motion by 8-10" also.

    If you can achieve this or even get somewhere near then you should be well on your way to improving your execution of one of the most difficult shots.

    If you want to shoot pool in style at your next pool tournament you can try it out here..

    << link to commercial website deleted by berkeman >>

    Last edited by a moderator: Feb 24, 2009
  9. Feb 24, 2009 #8


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    That's what I always thought, but it's not the way that I do it. I put opposite spin on the cueball. It has to be the spin imparted to the object ball that affects the shot that way.
    (And lest you think that I'm exaggerating, five of my friends are world-certified referees and they've all seen me do it.)

    Welcome to PF, Jonstewarts.
    You should be aware, though, that commercial links are against forum rules. I shoot with a Steel Stick, by the way.
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