Lets say an object ball is a few balls widths off the rail, and you are hooked. You kick into the rail at an angle so that it hits the object ball full. If you do hit the OB full, do you use top or bottom to get the cueball to draw back? Logic tells me that it would be reversed since the cueball is coming towards the OB at an opposite angle. So would you use topspin to draw the cueball off a kick shot? Or is it still draw, and can someone please explain the physics of it? Thanks
Kicking and Topspin/Bottom- Physics Experts Please Help
- Thread starter LowEnglish
- Start date
I am no physics expert, but I was a Physics major for the few semesters in college, so this is what I believe happens. Even if you use top spin when the cue ball hits the rail, the cue ball will have aquired top spin as it leaves the rail(not backspin). Part of the reason is that the cloth on the rail will grip the cue ball and spin it the other way. Since forces come in pairs, the cue ball is pushing against the rail with topspin, the rail is however pushing it back the other way. When the cue ball has completely compressed the rail, it is momentarily at rest. There is no spin. Once it starts being pushed off the rail it should have the spin the rail imparted on it. That is, when looking behind the cueball as it leaves the rail (opposite side from the shooter), it has topspin.
Here is an example of how spin can be reversed. Get a superball or rubberband ball and spin it with backspin and throw it forward a bit. When it hits the ground naturally it comes backward, but on the second bounce it goes forward again and so on. Spin on the ball grips ground, ground grips back and reverses the spin. This is not a perfect analogy I admit, but the simplest one I can think of right now.
Now there are other factors that come into play. The cueball actually sinks into the rail and because it contact above the equator of the cue ball, the rail will actually push the cue ball slightly into the table and the cueball leaves the table for a fraction of time. The harder you hit, the longer it leaves the table. In this case, the cue ball may have no spin and upon contact with the obect ball will stop dead (as in your example).
This is where my physics fails me. I did switch majors so if anyone wants to correct and pick up from here please do.
I believe however that it is possible with the right amount of topspin and speed of the kick, and an object ball very close to the rail, you might be able to produce some, though negligible amounts of draw. When I say negligible I mean a couple millimeters. However this could just be due to collision from ball to ball or other factors that I can't think of at 4am.
Here is an example of how spin can be reversed. Get a superball or rubberband ball and spin it with backspin and throw it forward a bit. When it hits the ground naturally it comes backward, but on the second bounce it goes forward again and so on. Spin on the ball grips ground, ground grips back and reverses the spin. This is not a perfect analogy I admit, but the simplest one I can think of right now.
Now there are other factors that come into play. The cueball actually sinks into the rail and because it contact above the equator of the cue ball, the rail will actually push the cue ball slightly into the table and the cueball leaves the table for a fraction of time. The harder you hit, the longer it leaves the table. In this case, the cue ball may have no spin and upon contact with the obect ball will stop dead (as in your example).
This is where my physics fails me. I did switch majors so if anyone wants to correct and pick up from here please do.
I believe however that it is possible with the right amount of topspin and speed of the kick, and an object ball very close to the rail, you might be able to produce some, though negligible amounts of draw. When I say negligible I mean a couple millimeters. However this could just be due to collision from ball to ball or other factors that I can't think of at 4am.
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The direction the cueball spins remains the same before and after contacting the cushion. The contact will only take some of the spin away. So, if you shoot top spin, the cueball will continue spinning along the direction of your cue after it has hit a cushion in any angle, if you shoot draw, the cueball will continue spinning along the direction of your cue, but towards the bumper. Well, I think you might a fraction of sidespin if you shoot a dead ball into a cushion at an angle, the cushion will give a fraction of "running side/english" on the cueball.
The contact between the rail and the cueball is still quite fast and the friction is quite low to make a significant change in the spin direction.
The contact between the rail and the cueball is still quite fast and the friction is quite low to make a significant change in the spin direction.
twilight said:
The spin does reverse with a superball on a smooth surface, but not with a billiard ball on a billiard cloth. The answer to the original question is topspin. Visualize it this way: the cueball will go into the rail spinning such that the top of the ball is spinning away from you. It comes back the cushion still spinning such that the top of the ball is spinning away from you. When it hits the back of the object ball, this type of spin is draw.
It takes quite a follow stroke to make the cue ball keep spinning after it comes back off the rail, though. Also note that unless you're shooting perpendicular to the rail, the topspin will make the cue ball curve after coming off the rail (picture the curved path of the cue ball after hitting a hard not-quite-straight shot with follow; the same concept makes the cue ball curve hitting the rail not-quite-straight with follow).
-Andrew
When you hit the rail with topspin, as mentioned above, the cueball will still be spinning in the direction you hit it. There is an old trick shot with one principle that you have probably encountered in a game. If you have an object ball very close to a hole and hit it nearly full with topspin, the cue ball will hit the ball in the pocket, hit the rail, and either kill or continue spinning forward and strike the rail more than once. The only difference is there is no second object ball after the rail. If there were, the cueball will strike that object ball and draw back toward the rail.
When you hit a ball with topspin, the cue will actually skid due to the topspin as it travels along the cloth. It it is still skidding when it hits an object ball, the cueball will follow through. If you draw, the reverse happens. The cueball is actually spinning backward as it slides forward on the cloth, and if it is still spinning backward when it hits the object ball, you will draw. Just imagine that the rail is an object ball. If you hit it with draw, it will still be spinning backwards when it hits the rail, and will follow after hitting the object ball. You will likely not be able to produce the same amount of draw after a rail as you can follow, because the rail sucks up most of the topspin when compressing. There is a longer contact time with the rubber than another object ball.
Someone correct me if I'm wrong, but that's how I understand it.
When you hit a ball with topspin, the cue will actually skid due to the topspin as it travels along the cloth. It it is still skidding when it hits an object ball, the cueball will follow through. If you draw, the reverse happens. The cueball is actually spinning backward as it slides forward on the cloth, and if it is still spinning backward when it hits the object ball, you will draw. Just imagine that the rail is an object ball. If you hit it with draw, it will still be spinning backwards when it hits the rail, and will follow after hitting the object ball. You will likely not be able to produce the same amount of draw after a rail as you can follow, because the rail sucks up most of the topspin when compressing. There is a longer contact time with the rubber than another object ball.
Someone correct me if I'm wrong, but that's how I understand it.
Both top and bottom spin can work depending on the nature of the rails. Most pros I've watched play the shot with draw. Normally the best you can achieve is a stop shot on impact with the OB after the kick.
Watch this highspeed video of topspin bouncing off the rail:
http://www.engr.colostate.edu/~dga/pool/high_speed_videos/HSV7-13.htm
Click next and watch the following 7 videos showing different spins bouncing of the rail. The 6th one is with draw where you can see the CB sliding for quite a distance.
Watch this highspeed video of topspin bouncing off the rail:
http://www.engr.colostate.edu/~dga/pool/high_speed_videos/HSV7-13.htm
Click next and watch the following 7 videos showing different spins bouncing of the rail. The 6th one is with draw where you can see the CB sliding for quite a distance.
Although I agree that the spin won't reverse to the extent of a superball on a smooth surface, I doubt you can get significant draw action on the cue ball after hitting a rail, regardless of how much topspin you impart on the CB.Andrew Manning said:
The reason is that for almost all follow shots, the rate at which the CB rolls (topspin) is directly proportional to its linear speed, since it is rolling naturally. In other words, the angular momentum is proportional to its linear momentum.
You would think that the greater the topspin, the more likely it will retain its spin after rebounding off a cushion. However, the greater the spin, the greater the linear speed, and thus the greater the coefficient of friction between the CB and the cushion upon contact. The friction acts to reduce/eliminate the spin of the CB (such as the extreme case of the superball).
Therefore, since the amount of friction is also proportional to the topspin (and speed) of the CB, I think things cancel out, such that you have roughly the same amount of resulting CB "backspin" (if you get any backspin at all) regardless of the incoming speed of the CB.
I'm just reasoning what seems to make sense in my head. I may be incorrect. I wish I had a table of my own so I can try it out.
LowEnglish said:
While the details depend on the rail gutter, the nose height, and the stickyness of the cloth on the cushion, the general result is that balls tend to lose all their top or bottom spin and come off a cushion sliding.
Unless you have unusually slick (i.e., new) cloth or have overspin, you're not gonna get draw after hitting an object ball off the cushion.
That's coming directly off the cushion though. Going into the cushion at an angle is a horse of a different color. You can get all sorts of wicked safeties hitting these kicks for a nearly full hit with draw. I suppose what's happening is the component of the backspin acting perpendicular to the rail is wiped out by the cushion, while the component acting parallel to the rail is still there and can be used to tuck the cueball in behind the second (offending) object ball.
mike page
fargo
Just a note: Hitting a ball dierectly into the cushion will have a reverse underspin or overspin on it. Note the ball did not change rotation, the rail assisted the english and the ball is spinning in the same direction. This is why it is important when hitting a cluster of balls from behind the rack to make sure that low english is used enabling the CB to make it through the cluster.
This effect rapidly approaches zero when shooting into an angle off the rail, instead it picks up side english (rail induced english). There are 3 cushion billiard shots that take advantage of rail english and rail-ball english which is why I think playing all the games is important.
This effect rapidly approaches zero when shooting into an angle off the rail, instead it picks up side english (rail induced english). There are 3 cushion billiard shots that take advantage of rail english and rail-ball english which is why I think playing all the games is important.
In addition to what the other posters have said, the dividing line is approximately at a 45 degree incoming angle to the cushion. If you're coming in at less than this, use draw. If greater, use follow. The cushion itself imparts a little bit of a draw component since the spin it puts on the ball is tilted by about 15.7 degrees from the vertical, which is due to the cushion being a little higher than the center of the cueball. (This is a completely useless fact but I thought interesting in this context ).LowEnglish said:
As Mike Page stated, the more perpendicular you come into a cushion, the more spin gets rubbed off. For a perfectly perpendicular shot at least, the amount of follow that is left (now effectively draw) is very sensitive to the amount of friction present and the cushion height. It may or may not have any spin left after it rebounds depending on the particular table.
If it has draw going into the cushion, all of it is removed. The difference is that, in the case of draw, friction with the cushion nose drives the ball down into the table bed (rail gutter), adding to the compressive downward force that the cushion applies to the ball (again due to nose height). So the ball experiences considerable friction from both the cushion and the bed, although much greater from the cushion.
In the case of topspin (follow) going in, the frictional force with the cushion nose opposes this downward compression force, and as a result there is very little overall downward force and thus friction with the bed.
As you make the incoming angle more shallow, the orientation of the friction force with cushion becomes less vertical and more horizontal. The torque from this is at a right angle to both the friction force and to the radius moment arm drawn from the center of the ball to cushion nose. This perpendicularity makes it go from less horizontal to more vertical. Since an angular momentum component always develops in the direction of the torque (the torque points in the direction of the newly developing spin axis), and since it is now more vertical, it won't cancel any existing follow or draw as readily since the angular momentum components for draw or follow are always horizontal. In brief, less spin is removed (although all of it might still be removed until the angle becomes shallow enough).
Well, you asked for a physics explanation. Hope it helped a little.
Jim
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