# Reverse Throw

#### RicNic

##### Registered
Does anyone know how much reverse throw is applied to the cue ball when throw is applied to the object ball?

#### realkingcobra

##### Well-known member
Silver Member
Does anyone know how much reverse throw is applied to the cue ball when throw is applied to the object ball?

Wouldn't that apply to the shot at hand?

#### Bambu

##### Dave Manasseri
Silver Member
Never heard of reverse throw, reverse spin maybe? Still confused, how can you apply anything to the cueball from the object ball?

#### DallasHopps

##### AzB Silver Member
Silver Member
I was under the impression that throw happens due to the friction between cue/object ball allowing the object ball to change it's path in the direction the cueball strikes it.
Under that assumption, no "reverse throw" is or can be applied unless the cueball hits the object ball, throwing it, and then the object ball goes 3 rails and hits the cueball, throwing it.

#### OnTheMF

##### I know things
Silver Member
Does anyone know how much reverse throw is applied to the cue ball when throw is applied to the object ball?

I didn't bother to look anything up, so this could be wrong, but I believe the answer is none. The force line of any throw is parallel to the tangent line, so the only effect throw could have on the CB is a infinitesimal reduction in speed.

#### Black-Balled

##### AzB Silver Member
Silver Member
Wouldn't that apply to the shot at hand?

As a result of the many variables...agreed.

#### desmocourtney

##### AzB Silver Member
Silver Member
Every action has an equal and opposite reaction, I think.

#### Cdryden

Silver Member
Does anyone know how much reverse throw is applied to the cue ball when throw is applied to the object ball?

This depends on how much spin the CB has to begin with, the impact force and the speed at which the CB is traveling into the object ball. Other factors would be the cloth (slow of fast) and the balls (clean or dirty).

It will also depend on how full/thin you hit the object ball. (only because hitting the OB full changes the direction of the CB more than a thin hit)

But for most shots I don't think it will not reverse the spin, more than likely it will just reduce the amount of spin left on the CB.

#### jsp

##### AzB Silver Member
Silver Member
But for most shots I don't think it will not reverse the spin...
If the CB has very little inside english spin before contact, I can see how throw can reverse the spin of the CB post contact.

...more than likely it will just reduce the amount of spin left on the CB.
Actually, the opposite is true on outside english shots provided the amount of OE spin on the CB is insufficient for perfect "gearing" english (the resulting shot will have positive throw). In this case, the CB will have more OE spin than it started out with.

#### Jal

##### AzB Silver Member
Silver Member
If the CB has very little inside english spin before contact, I can see how throw can reverse the spin of the CB post contact.

.....

Actually, the opposite is true on outside english shots provided the amount of OE spin on the CB is insufficient for perfect "gearing" english (the resulting shot will have positive throw). In this case, the CB will have more OE spin than it started out with.
Jsp, for what it's worth, I agree with both of your observations.

RicNic said:
Does anyone know how much reverse throw is applied to the cue ball when throw is applied to the object ball?
Exactly the same amount, but in the opposite direction along the tangent line.

For instance, the cueball has a certain component of velocity in the direction of the tangent line, call it Vct. If the object ball is thrown in the same direction with velocty Vot, then the cueball's new velocity along the tangent will be Vct - Vot. If the object ball is thrown in the opposite direction along the tangent line because of excessive outside english, then the cueball's new velocity will be Vct + Vot.

This is just Newton's Third Law of action/reaction.

Jim

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#### Cdryden

Silver Member
If the CB has very little inside english spin before contact, I can see how throw can reverse the spin of the CB post contact.

Actually, the opposite is true on outside english shots provided the amount of OE spin on the CB is insufficient for perfect "gearing" english (the resulting shot will have positive throw). In this case, the CB will have more OE spin than it started out with.

True, in that case. But as I stated in the beginning of my reply, the outcome depends on several factors. You could probably come up with six different scenarios and get six different results. Since the OP didn't specify a particular shot I was trying to generalize.

#### TATE

##### AzB Gold Mensch
Silver Member
Does anyone know how much reverse throw is applied to the cue ball when throw is applied to the object ball?

I'm not versed in physics but my experience on the table is the cue ball throws a lot less than the OB on most spin throw cut shots. In other words, the cue ball's path is not changed that I can tell. I think the reason why is because the cue ball has forward momentum vesus a stationery OB, so minor force of the gearing effect does not have much effect on the forward momentum of the cue ball.

On perfectly straight in shots, or nearly straight shots, then I think the forces would be more equal and it's possible to throw the cue ball using side spin.

Maybe Dr. Dave or Bob Jewett has something that addresses this.

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#### Cornerman

##### Cue Author...Sometimes
Gold Member
Silver Member
Does anyone know how much reverse throw is applied to the cue ball when throw is applied to the object ball?

I like the question. In fact, I love the question. The examination and answer should open up a lot of eyes for both stop/stun shots and cut shots.

Freddie <~~~ yeah, no wonder I scratched

#### RobertR

##### WWSLD
Silver Member
Only Mike Page knows the answer to this question.

#### TATE

##### AzB Gold Mensch
Silver Member
I like the question. In fact, I love the question. The examination and answer should open up a lot of eyes for both stop/stun shots and cut shots.

Freddie <~~~ yeah, no wonder I scratched

#### Bob Jewett

##### AZB Osmium Member
Staff member
Gold Member
Silver Member
Jsp, for what it's worth, I agree with both of your observations.

Exactly the same amount, but in the opposite direction along the tangent line.

For instance, the cueball has a certain component of velocity in the direction of the tangent line, call it Vct. If the object ball is thrown in the same direction with velocty Vot, then the cueball's new velocity along the tangent will be Vct - Vot. If the object ball is thrown in the opposite direction along the tangent line because of excessive outside english, then the cueball's new velocity will be Vct + Vot.

This is just Newton's Third Law of action/reaction.

Jim
Another way to put it is that the object ball is thrown by the slightly sticky surface of the cue ball pulling it to the side. Since the cue ball is not attached to the table, it will have be pushed in the other direction. Depending on the situation, the cue ball will be going faster or slower along the tangent line right after the contact due to that frictional force against the object ball.

#### RicNic

##### Registered
Thanks to all for considering this question. As a number of you have suggested, there is an equal and opposite reaction on the cue ball, the magnitude and direction, of which, depend upon the specific conditions, i.e., stun, draw, etc. Published papers on this concept appear to be in need of correction if they say that there is none or very little effect on the cue ball's motion. We would all benefit if someone would explore this effect in some mathematical way, and applied in a practical way.

#### MitchAlsup

##### AzB Silver Member
Silver Member
The CB departs on the tangent line defined by conservation of momentum when throw is applied. To the tangent line is altered in exactly the same way as the line of departure for the OB is altered by the throw.

#### Cornerman

##### Cue Author...Sometimes
Gold Member
Silver Member

No, I can't!!!

The answer starts pointing at tangents and the theory of tangents. I think that because of the velocity vectors, the throw for the cueball is in the same direction as its "tangent line path," but the throw for the object ball is perpendicular to its direction of line of centers creating a different angle.

Therefore, the vector of the cueball might be tangent to the contact point line of centers, but the path of the cueball is not perpendicular to the path of the object ball.

Freddie <~~~ now somebody set me straight

#### Bob Jewett

##### AZB Osmium Member
Staff member
Gold Member
Silver Member
Thanks to all for considering this question. As a number of you have suggested, there is an equal and opposite reaction on the cue ball, the magnitude and direction, of which, depend upon the specific conditions, i.e., stun, draw, etc. Published papers on this concept appear to be in need of correction if they say that there is none or very little effect on the cue ball's motion. We would all benefit if someone would explore this effect in some mathematical way, and applied in a practical way.
Well, in some sense there is less effect on the cue ball's motion than on the object ball. Suppose the cue ball lands full on the object ball at a speed of 10 inches per second and with enough spin to give the object ball a speed to the side of 1/2 inch per second (a "slope" of 20:1, or about 3 degrees of throw). Suppose the cue ball has no draw or follow. The cue ball will be moving to the other side at 1/2 inch per second. If the rolling friction on the cloth is such that the cue ball rolls one inch to the side before stopping, the object ball will roll about 400 times as far in total (assuming it doesn't hit a cushion) for a total distance of 400 inches roughly. With a slope of 20:1 off dead straight ahead, that means it will go to the side 20 inches in its 400 inches of travel. If you count "total distance to the side" as the important parameter, there was more effect on the OB than the CB.

Of course, it would have to be a pretty large table to have a 400-inch clear path, but if the object ball went a more reasonable 80 inches before a rail, it would have gone to the side 4 inches in that distance.