Physics of Spin and speed off a rail

[zpele]

Alright so I was puzzling over this the other day...

We all know that in Physics every action has an equal and opposite reaction.

Now lets look at an example from pool that has me confused.

Using the exact same stroke and speed from the same spot on the table you hit the cueball at an obtuse angle into the rail.

The first shot you use exact middle english. The cueball hits the rail and some of the power is absorbed into the rubber making it lose speed.

The second shot you hit two cuetips off to the left or right (depending on whichever is running english off the chosen rail). When the cueball hits the rail it shoots off with more speed than it went into it because of the spin.

Why does this happen if you are exerting the exact same amount of force to the cueball?

Where does the force go when you hit the center of the cueball?

 

[softshot]

the spinning ball grips the rail this is where the force is multiplied or reduced depending on the spin

sidespin off of a rail alters the angles.. one type of spin is known as running english this spin grips the rail in the direction of travel and accelerates the ball.. and widens the angle

the other type of spin is reverse or kill english.. this english grips the rail opposite of the direction of travel and has a braking effect that slows the ball down..and shortens the angle


in your experiment if you shoot perpendicular to the rail .. left or right english will cause the ball to rebound to either the left or right.. being perpendicular there is no running or reverse..but only when perpendicular..

when the line into the rail is left of perpendicular..right english is running english and left english is reverse

when the line into the rail is right of perpendicular you get the opposite...

it's a lot easier to show at the table but I hope this helps

 

[zpele]

the spinning ball grips the rail this is where the force is multiplied or reduced depending on the spin

sidespin off of a rail alters the angles.. one type of spin is known as running english this spin grips the rail in the direction of travel and accelerates the ball.. and widens the angle

the other type of spin is reverse or kill english.. this english grips the rail opposite of the direction of travel and has a braking effect that slows the ball down..and shortens the angle


in your experiment if you shoot perpendicular to the rail .. left or right english will cause the ball to rebound to either the left or right.. being perpendicular there is no running or reverse..but only when perpendicular..

when the line into the rail is left of perpendicular..right english is running english and left english is reverse

when the line into the rail is right of perpendicular you get the opposite...

it's a lot easier to show at the table but I hope this helps

Thanks for the response...

I think I just figured it out.

In order to understand this phenominom and how it applies to spin off a rail I had to think about how spin on the cueball applies when an object ball is hit.

The object ball is not a static object and thus takes some or all of the spin from the cueball. Hence the force of the object ball is directly proportionate to the force on the cueball. If the cueball is not spinning when it hits the object ball only one type of force is being applied. If the cueball is spinning when it hits the object ball there is more than one type of force being applied and the object ball reacts in two ways instead of one.

Now if you think about a rail it can be considered for most intents and purposes a static object. Because the rail is a static entity most force stays on the cueball.

Last we need to consider that a rail is not entirely static and gives a little when hit. This give absorbs some of the force of the cueball and thereby reduces the amount of speed for the cueball coming off the rail. It also translates any spin into an opposite force.

If you hit the rail with straight top it will come off at the exact opposite angle it went into the rail with but with reduced speed because of friction and the give of the rail itself.

If you hit the rail with running english the forward spin of the cueball does the same thing as the above paragraph but because there is also sidespin that force has to go somewhere it cant just disappear (hence the Physics rule of every force has an equal and opposite reaction). This spin is translated into increased speed off the rail.

Let me know if I'm way off base this is more a stream of consciousness and it might not flow well.

 

[thommy]

Don't need to know why, just accept it and go with it

Just kidding, sorta, I think you are correct, but I'll wait for the physicists to respond . . .

 

[Tony_in_MD]

What is the last thing that goes through a fly's mind...

If a fully loaded train is traveling down the track at 120 MPH and a fly hits it head on......


Sorry, the devil made me post this.

 

[krupa]

The simple answer is that the physics (i.e., forces at work) of spinning bodies is a lot different than non-spinning bodies.

Here's the long answer: http://www.sfbilliards.com/shepard_apapp.pdf

 

[zpele]

The simple answer is that the physics (i.e., forces at work) of spinning bodies is a lot different than non-spinning bodies.

Here's the long answer: http://www.sfbilliards.com/shepard_apapp.pdf

Sweet that is exactly what I was looking for.

 

[Bob Jewett]

One other thing to note is that the speed of the ball away from the cushion is still less than the speed into the cushion. The total speed of the cue ball may increase because the speed parallel to the cushion is increased by the side spin. If a ball goes diagonally into a corner with a lot of running side spin, it may come out of the corner at a higher speed (and nearly along the same line it went in on) but that's because it got two sideways boosts on the two cushions.

 

[zpele]

One other thing to note is that the speed of the ball away from the cushion is still less than the speed into the cushion. The total speed of the cue ball may increase because the speed parallel to the cushion is increased by the side spin. If a ball goes diagonally into a corner with a lot of running side spin, it may come out of the corner at a higher speed (and nearly along the same line it went in on) but that's because it got two sideways boosts on the two cushions.

Yes this is what I thought but it took me a few days of heavy brain use to deduct it. People must have been looking at me weird because i was just spinning a cueball into a side rail with my hand for about an hour with this confused expression on my face.

 

[mfinkelstein3]

Cue ball forces

Tom Simpson explains this the best. The cue ball has two forces, one a forward force and the other a spin (rotational) force.

With a center ball, only the forward force is acting and as Bob says, some of the energy is eaten up by the rail.

With spin, the forces are the forward force plus the spin force minus the energy the rail absorbs.

Hope that helps

 

[greyghost]

Alright so I was puzzling over this the other day...

We all know that in Physics every action has an equal and opposite reaction.

Now lets look at an example from pool that has me confused.

Using the exact same stroke and speed from the same spot on the table you hit the cueball at an obtuse angle into the rail.

The first shot you use exact middle english. The cueball hits the rail and some of the power is absorbed into the rubber making it lose speed.

The second shot you hit two cuetips off to the left or right (depending on whichever is running english off the chosen rail). When the cueball hits the rail it shoots off with more speed than it went into it because of the spin.

Why does this happen if you are exerting the exact same amount of force to the cueball?

Where does the force go when you hit the center of the cueball?

The spinning force that makes the cue zip off the rail when using running english is GYROSCOPIC PRECESSION, Earl does this extremely well

http://www.youtube.com/watch?v=IUgn_z7i_6I&feature=related (earl)

http://www.youtube.com/watch?v=OQX_H8GxZRc (blackjack)

hope that helps......you can even look up GYROSCOPIC PRECESSION on here and a good thread on it comes up (minus the small flame war....oldie but goodie)

best wishes,
Greyghost

 

[bbb]

The spinning force that makes the cue zip off the rail when using running english is GYROSCOPIC PRECESSION, Earl does this extremely well

http://www.youtube.com/watch?v=IUgn_z7i_6I&feature=related (earl)

http://www.youtube.com/watch?v=OQX_H8GxZRc (blackjack)

hope that helps......you can even look up GYROSCOPIC PRECESSION on here and a good thread on it comes up (minus the small flame war....oldie but goodie)

best wishes,
Greyghost

wish i could make the cue ball do that (espeially earls shot)....

 

[greyghost]

Bbb in the thread I was talking about there's a good drill that will help u to learn to hit that stroke better. The shot is useful an comes in many forms u can use it with follow an draw alike, some are not nearly as highly difficult as earls an most are not as tough to execute as one might think.

Go search
How to force follow like Strickland

That's the thread where we talk all about it an I go over that drill Brian jones showed me some time ago

 

[Bob Jewett]

The spinning force that makes the cue zip off the rail when using running english is GYROSCOPIC PRECESSION, ...

I think that technically, the action off the cushion has nothing to do with "gyroscopic precession". In fact since the ball has no major axis, the development of its spin during shots has more or less nothing to do with gyroscopes.

 

[greyghost]

As usual I was simply generalizing. But to a degree wouldn't it be close to a form of Torque-free gyroscopic precession?

Something to the effect as Forward motion pushes the ball into the cushion,the side spin "peels out" on the cushion face an sort of sling shots.....sort of how they get around the moon. Well not sort of but that's what comes to mind....it's breaking the friction coefficient or some cient lol

 

[Bob Jewett]

... But to a degree wouldn't it be close to a form of Torque-free gyroscopic precession? ...

All gyroscopic action necessarily involves both torque and angular momentum.

I've heard others use the word "gyroscopic" in relation to what pool balls do, but I don't think it's ever been used correctly.

 

[bbb]

Bbb in the thread I was talking about there's a good drill that will help u to learn to hit that stroke better. The shot is useful an comes in many forms u can use it with follow an draw alike, some are not nearly as highly difficult as earls an most are not as tough to execute as one might think.

Go search
How to force follow like Strickland

That's the thread where we talk all about it an I go over that drill Brian jones showed me some time ago

i did the search and found your post
im going to start working on it
so that anyone else wants to know im going to quote your post
THANK YOU FOR RESPONDING :thumbup:
from grey ghost
Brian Jones showed me a drill to work on that I guess about 5/6 years ago.

You use just the striped balls, place two inline about 3-5 foot apart depending on how hard the drill is for you. Hit the horizontal plane on the "CB" and use at least a good couple tips of side left or side right.

If you do it right the "CB" will hit the OB and pocket it, and the "CB" will stay in place (horizontal plane w/speed is just a stop shot) and SPIN its butt off either left or right depending on the side you put on it.

Now quickly b/f the spin fades put another stripe in place for your "CB" and stroke the shot with the OPPOSITE Side english you just shot the first shot with.

Perfect would be 7/7 with the 9-15 balls. If the "CB" that became the OB stops spinning b/f you shoot at it then you have to start over. If you miss thats ok too, just as long as the "CB" kills and stays in its place for the next shot and maintains its spin.

VERY TOUGH & DEMANDING DRILL.....

its not for beginners, and intermediate level players will def have a super tough time with it......advanced level players only basically.

If your a beginner or intermediate player and you don't feel like torturing yourself then just shoot the shot 1 at a time. Just set it up, and try and pocket the ball and see how well you can keep the "CB" spinning in place after contact.

Like Bob said 30sec would be basically a maximum to retain spin......If you can do this and keep it spinning for more than 12-15 sec your doing well with it. But to do the actual drill your going to need to consistently maintain a 20 sec or more average spin time as it takes you about 10sec to get the ball in place for the next shot and then another 10sec to shoot.

Like I said this is a VERY TOUGH DRILL, don't let it get the best of you....b/c it will if you let it aggravate you.

Stay focused and take it one step at a time, and no matter how bad you do find at least one good thing that you did well/correctly. Don't ever finish a practice session all beat up, even if you are look on the bright side and find at least one positive note in regards to the session. Its practice, you will make mistakes, but better to make them there than in a live match or tournament.

best wishes,
-Grey Ghost-

 

[greyghost]

All gyroscopic action necessarily involves both torque and angular momentum.

I've heard others use the word "gyroscopic" in relation to what pool balls do, but I don't think it's ever been used correctly.

Well Bob we are always trying to better define the effects in the game, how would you say the effect we speak of be called or defined in your professional opinion?

All the best,
Greyghost

 

[Bob Jewett]

Well Bob we are always trying to better define the effects in the game, how would you say the effect we speak of be called or defined in your professional opinion?

All the best,
Greyghost

I think simply saying that the side spin of the ball rubs on the cushion which gives a force to the side and consequently speed to the side is sufficient. I think it is a mistake to get too technical without a real good reason. A student only has to see the action once or twice and then do it once or twice to understand it. A spotted cue ball helps.

 

[greyghost]

I think simply saying that the side spin of the ball rubs on the cushion which gives a force to the side and consequently speed to the side is sufficient. I think it is a mistake to get too technical without a real good reason. A student only has to see the action once or twice and then do it once or twice to understand it. A spotted cue ball helps.

Good point.......K.I.S.S.:wink: