Collision Induced Throw

L

LAMas

AzB Silver Member
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The geometric cut angle for CTE is 30 degrees. What is actually happening to cause the OB to travel at around 25 degrees after contact.

"Throw is imparted to a ball by collision from a cue ball with no english on it through friction. This is sometimes called "collision-induced throw". The direction of the object ball's throw depends on the cue ball's path immediately before impact. Collision-induced throw "pushes" the object ball in the same direction as the cue ball was traveling before impact. Thus, a cue ball traveling from the left will cause an impacted object ball to be thrown slightly to the left of the OB's natural impact line."
Wiki

Is it because of the forward motion of the CB "pushes" the OB in a combination of this forward direction/motion and in the CP on the CB to the CP on the OB (30 degrees for CTE) direction at the same time before the OB starts to roll at around 25 degrees?

Is there a high speed vid of what is happening with the 30 degree line from the base of the OB before the collision with the CB drawn on the cloth?

Thanks.
 
alphadog

alphadog

AzB Silver Member
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LAMas said:
Thanks,
I saw that before but I wish/want to see the geometrically correct line on the cloth and the line that the OB actually takes. Does the OB actually move forward before rolling?

Be well
Click to expand...

Yes greater the speed, more it moves.
 
ENGLISH!

ENGLISH!

Banned
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LAMas said:
The geometric cut angle for CTE is 30 degrees. What is actually happening to cause the OB to travel at around 25 degrees after contact.

"Throw is imparted to a ball by collision from a cue ball with no english on it through friction. This is sometimes called "collision-induced throw". The direction of the object ball's throw depends on the cue ball's path immediately before impact. Collision-induced throw "pushes" the object ball in the same direction as the cue ball was traveling before impact. Thus, a cue ball traveling from the left will cause an impacted object ball to be thrown slightly to the left of the OB's natural impact line."
Wiki

Is it because of the forward motion of the CB "pushes" the OB in a combination of this forward direction/motion and in the CP on the CB to the CP on the OB (30 degrees for CTE) direction at the same time before the OB starts to roll at around 25 degrees?

Is there a high speed vid of what is happening with the 30 degree line from the base of the OB before the collision with the CB drawn on the cloth?

Thanks.
Click to expand...

Big E,

Also keep in mind that upon the collision both balls, OB & CB pick up an outside rotation or spin or english or 'roll' from the collision of the balls.

If the OB picks up what is 'outside' spin it is as though it was hit by a CB with inside spin. (if isolated out of the full picture)

I know you know this, but I just thought it was good to bring into the thinking.

There is much going on & too many times a parameter is left out of 'conversations', for what ever reason.

When I first came on AZB I referred to something & used the word 'push'. I was almost immediately led to The Guillotine by the politically correct science 'followers'.

I hope someone has a slowmo but I am not sure you would even be able to see too much as you would probably need to see it from both the horizontal & vertical perspective & I doubt there would be two slowmo cameras for the one occurrence.

But all we need to know is that it 'pushes'.

You Be, Stay, & Shoot Well.
 
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L

LAMas

AzB Silver Member
Silver Member
Spin.
In the vid, the OB has a line created by the white and black hemispheres aimed at the intended direction/path of the OB. After contact, instead of rolling with that line centered, the OB is rotating CCW causing it to "swerve?" before it starts rolling on its final path. Is it like throwing a curve ball? Is friction required between the OB and the cloth?

If I was inclined, I could go frame by frame and draw the geometrically correct line and plot the position of the center of the OB after impact to see if it curves into its new/final direction that it rolls caused by the spin...or not. Does this instead happen instantaneously at contact and the spin has no effect?

Be well
 
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B

bdorman

Dead money
Silver Member
I'm not sure if this answers your question but: 1) for OB spin to effect the path of the ball, the OB needs to be in contact with the cloth, and 2) all balls leave the cloth when they begin moving. The time "off the cloth" might only be 1mm for a soft shot or 2ft for a power draw shot -- it all depends on the speed of the shot: more speed = more time off the cloth.

That's why there's less CIT on a high-speed shot than a low-speed shot. Less time the OB is in contact with the cloth.

It's the same principal as the amount of time (distance) the CB will remain on the tangent line after striking an OB.
 
K

ktrepal85

Banned
LAMas said:
Spin.
In the vid, the OB has a line created by the white and black hemispheres aimed at the intended direction/path of the OB. After contact, instead of rolling with that line centered, the OB is rotating CCW causing it to "swerve?" before it starts rolling on its final path. Is it like throwing a curve ball? Is friction required between the OB and the cloth?

If I was inclined, I could go frame by frame and draw the geometrically correct line and plot the position of the center of the OB after impact to see if it curves into its new/final direction that it rolls caused by the spin...or not. Does this instead happen instantaneously at contact and the spin has no effect?

Be well
Click to expand...

The change of direction happens instantaneously during the collision. The reason it happens is that the balls stick together momentarily and during that moment the object ball is jerked in the direction of the cue ball's momentum slightly. I hope that makes sense.

I think you are confusing the 30 degree concept. Throw is always present it is just maximized at a 30 degree angle.

When thinking about throw i think it's easiest to image a merri-go-round spinning on a playground. If you were to walk into it at a 30 degree angle you would be jerked and your direction would change. If you walk into just barely the edge of it you wouldnt feel nearly as much jerk therefore your walk path wouldnt change much. So basically the more solid of a hit the more throw. Good luck!
 
JohnnyP

JohnnyP

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The cut induced spin is readily seen in that video. That makes it easier to understand why some banks go way short, and for other banks, use it to turn a ball.
 
J

Jal

AzB Silver Member
Silver Member
LAMas said:
Spin.
In the vid, the OB has a line created by the white and black hemispheres aimed at the intended direction/path of the OB. After contact, instead of rolling with that line centered, the OB is rotating CCW causing it to "swerve?" before it starts rolling on its final path. Is it like throwing a curve ball? Is friction required between the OB and the cloth?

If I was inclined, I could go frame by frame and draw the geometrically correct line and plot the position of the center of the OB after impact to see if it curves into its new/final direction that it rolls caused by the spin...or not. Does this instead happen instantaneously at contact and the spin has no effect?

Be well
Click to expand...
The induced spin on the OB has essentially no effect on its direction, unless a bouncing cueball contacts it above center. (In principle, follow or draw on the cueball, even without any bouncing, will produce a slight swerving effect. But this effect is so small you'd have to do a very precise measurement to detect it. Random buffeting by the cloth might mask it even then.)

To see why the cloth can't have anything but a negligible effect, consider the forces involved. During the collision, the force (compression) acting along the line of centers between the CB and OB generally is in the area of thousands of pounds. The friction force alone, acting along the tangent line/plane and responsible for throw, is several tens of pounds (50 lbs or more is not unusual). Contrast this to the friction from the cloth, which is only a fraction of an ounce! It's as if the collision takes place while the balls are floating above the table's surface.

Jim
 
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Bob Jewett

Bob Jewett

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LAMas said:
Thanks,
I saw that before but I wish/want to see the geometrically correct line on the cloth and the line that the OB actually takes. Does the OB actually move forward before rolling?...
Click to expand...
So far as is known, the OB and CB move while in contact much less than a mm. After that, the OB leaves contact with the cue ball and travels in a straight line. If the OB curves at all it is not observable. For all practical purposes, the path of the thrown OB is a straight line from its starting point that is at a small angle (the angle of throw) from the line of centers at the instant of the collision.
 
dr_dave

dr_dave

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LAMas said:
Thanks,
I saw that before but I wish/want to see the geometrically correct line on the cloth and the line that the OB actually takes.
Click to expand...
The following video has more of what you want for different amounts of sidespin:

HSV B.33 - Outside english gearing, and cut and spin-induced throw

LAMas said:
Does the OB actually move forward before rolling?
Click to expand...
Yes, the OB always starts out with stun (unless the CB has topspin or bottom spin, which can transfer as a small amount of opposite spin on the OB).

BTW, the phrase "cut induced throw (CIT)" is more modern and more accurate. It is the cut angle that causes the throw (or spin, in the case of SIT), not the "collision."

Also, probably the best video dealing with throw concepts is:

NV B.86 - Cut-induced throw (CIT) and spin-induced throw (SIT), from VEPS IV

If you haven't seen this (or haven't seen it lately), check it out.

And much more info (inluding numerous other videos and detailed and well illustrated instructional articles dealing with throw) can be found here:

squirt, swerve, and throw effects resource page

I think the videos, articles, and resource page answer pretty much every question possible concerning throw.

Enjoy,
Dave
 
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L

LAMas

AzB Silver Member
Silver Member
bdorman said:
I'm not sure if this answers your question but: 1) for OB spin to effect the path of the ball, the OB needs to be in contact with the cloth, and 2) all balls leave the cloth when they begin moving. The time "off the cloth" might only be 1mm for a soft shot or 2ft for a power draw shot -- it all depends on the speed of the shot: more speed = more time off the cloth.

That's why there's less CIT on a high-speed shot than a low-speed shot. Less time the OB is in contact with the cloth.

It's the same principal as the amount of time (distance) the CB will remain on the tangent line after striking an OB.
Click to expand...

I think that some collisions can make the balls leave the cloth especially with more speed, but a slow rolling OB may not have all of its mass against the cloth but can still be in contact with it. At rest, the mass of the ball is a force vector straight down but at collision it can become mostly forward on the line of centers and less down.

With that said, I concur with your post and thanks for the heads up.

Be well.
 
L

LAMas

AzB Silver Member
Silver Member
ktrepal85 said:
The change of direction happens instantaneously during the collision. The reason it happens is that the balls stick together momentarily and during that moment the object ball is jerked in the direction of the cue ball's momentum slightly. I hope that makes sense.

I think you are confusing the 30 degree concept. Throw is always present it is just maximized at a 30 degree angle.

When thinking about throw i think it's easiest to image a merri-go-round spinning on a playground. If you were to walk into it at a 30 degree angle you would be jerked and your direction would change. If you walk into just barely the edge of it you wouldnt feel nearly as much jerk therefore your walk path wouldnt change much. So basically the more solid of a hit the more throw. Good luck!
Click to expand...

The CB and OB are welded together for that instant on a cut shot and I accept that They travel to some degree in the direction of the CB before separation and that contributes to the path of the OB after contact.

CTE is geometrically a 30 degree cut on the line of centers and not just a concept to me.

Thanks for your explanation.

Be well
 
L

LAMas

AzB Silver Member
Silver Member
Jal said:
The induced spin on the OB has essentially no effect on its direction, unless a bouncing cueball contacts it above center. (In principle, follow or draw on the cueball, even without any bouncing, will produce a slight swerving effect. But this effect is so small you'd have to do a very precise measurement to detect it. Random buffeting by the cloth might mask it even then.)

To see why the cloth can't have anything but a negligible effect, consider the forces involved. During the collision, the force (compression) acting along the line of centers between the CB and OB generally is in the area of thousands of pounds. The friction force alone, acting along the tangent line/plane and responsible for throw, is several tens of pounds (50 lbs or more is not unusual). Contrast this to the friction from the cloth, which is only a fraction of an ounce! It's as if the collision takes place while the balls are floating above the table's surface.

Jim
Click to expand...

"To be different, it must make a difference" so the imparted spin on the OB doesn't affect the final path of the OB but instead it is only an incidental byproduct of the collision . The final path of the OB for CTE not being on he line of centers and is less than 30 degrees was determined by the forces at play during the collision.

I too thought about what happens if the CB and OB were launched off of the cloth due to enough force/s at play during the collision.

As always, thanks for your descriptive examples.

Be well.
 
L

LAMas

AzB Silver Member
Silver Member
Bob Jewett said:
So far as is known, the OB and CB move while in contact much less than a mm. After that, the OB leaves contact with the cue ball and travels in a straight line. If the OB curves at all it is not observable. For all practical purposes, the path of the thrown OB is a straight line from its starting point that is at a small angle (the angle of throw) from the line of centers at the instant of the collision.
Click to expand...

I concur, but seeing the OB spinning CCW after contact in the slo mo vid made me wonder.

Considering what has been proffered in this thread, the spinning might only take place while the OB is not touching the cloth and starts rolling with no spin once it again makes contact with the cloth due to frictional forces.

So far as is known, which may be the truth or not, the observed OB spin does not affect the OB final path that is a straight line without an initial curve that I wondered about.

Thanks for your qualified reply.

Be well
 
L

LAMas

AzB Silver Member
Silver Member
dr_dave said:
.....
BTW, the phrase "cut induced throw (CIT)" is more modern and more accurate. It is the cut angle that causes the throw (or spin, in the case of SIT), not the "collision."
.....
Enjoy,
Dave
Click to expand...

I used the Wiki wording and I have been aboard with cut instead of collision for throw can only exist with a cut, whereas a collision can exist without throw.

I have seen most of those vids and have understood their lessons for years.

They fortify my experiences with pool by visualizations that are shared for free.

What they lack for me is the precise reason why the OB cannot follow the line of centers when a center hit on the CB as in CTE. A graph of the path of the OB from initial contact to rolling on a straight line at every microsecond could be conclusive evidence.

In the end, my question is academic and of no practical utility.

As always, thanks for your post an all of the information you share for all to see.....for free.

Be well good doctor.
 
dr_dave

dr_dave

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Gold Member
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LAMas said:
I have seen most of those vids and have understood their lessons for years.

They fortify my experiences with pool by visualizations that are shared for free.

What they lack for me is the precise reason why the OB cannot follow the line of centers when a center hit on the CB as in CTE.
Click to expand...
The only way the OB could head in the line of centers direction would be if the force from the CB were only in the line of centers direction. This could happen only if the balls were frictionless, which is possible only theoretically. Because there is friction with real pool balls, any sideways rubbing between the balls due to cut angle or spin causes a throwing force. The throwing force pushes the OB away from the line-of-centers direction (and transfers sidespin to the OB). BTW, good illustrations of these effects can be found in the following articles (and the effects are clear in the referenced videos):

"Throw - Part I: introduction" (BD, August, 2006)

LAMas said:
As always, thanks for your post an all of the information you share for all to see.....for free.
Click to expand...
You're very welcome, and thank you for the kind words.

I aim to swerve. ;)

LAMas said:
Be well good doctor.
Click to expand...
You to.

Best regards,
Dave
 
dr_dave

dr_dave

Instructional Author
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LAMas said:
Jal said:
The induced spin on the OB has essentially no effect on its direction, unless a bouncing cueball contacts it above center. (In principle, follow or draw on the cueball, even without any bouncing, will produce a slight swerving effect. But this effect is so small you'd have to do a very precise measurement to detect it. Random buffeting by the cloth might mask it even then.)

To see why the cloth can't have anything but a negligible effect, consider the forces involved. During the collision, the force (compression) acting along the line of centers between the CB and OB generally is in the area of thousands of pounds. The friction force alone, acting along the tangent line/plane and responsible for throw, is several tens of pounds (50 lbs or more is not unusual). Contrast this to the friction from the cloth, which is only a fraction of an ounce! It's as if the collision takes place while the balls are floating above the table's surface.
Click to expand...
... so the imparted spin on the OB doesn't affect the final path of the OB but instead it is only an incidental byproduct of the collision.
Click to expand...
Bingo!

Well stated, Jim.

Practically speaking, the cloth has absolutely no affect on throw or cling/skid/kick, as some people might think. For more info, see the cling/skid/kick resource page.

Regards,
Dave
 
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