Interesting thing about half ball hits

N

nrhoades

AzB Silver Member
Silver Member
I was looking at some of Dr. Dave's proofs and noticed something interesting. I'm sure that most of you know about this, but at least myself and one of my friends didn't, so I'll share.

I did some calculations to see how much aiming error I can play with and still scratch from the foot spot. The cue ball trajectory (of a naturally rolling cueball) after a collision with another ball peaks out at about 38 degrees as a function of OB angle. This peak is right around a half ball hit (30 degrees for OB). For a +/- 1 degree variance in the post collision cue ball angle, the OB has a variance of +/- 7 degrees. This is pretty big.

What this means, is that in the attached pictures, you can hit the object ball into any part of the red zone and the cue ball will always end up in the white zone. The exact angles may vary from table to table, but the idea is the same.

This must be one of the reasons why I see carom players aim for the edge of the ball often.
 

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nrhoades:

The half-ball hit is probably the most useful shot in the pool player's arsenal (and can also be a pain in the taint), for several reasons:

1. The margin of error, as you've well noted, is significant -- you can hit a large variance around the edge of the object ball, yet the cue ball's carom trajectory is nearly the same.

2. The path of the object ball and the cue ball, as well as their SPEED, is very predictable. In fact, on a table with a normal cue ball (i.e. same size and mass as the object balls themselves), a half-ball hit results in the cue ball losing 50% of its kinetic energy, and the object ball inheriting that 50% kinetic energy. Result? The cue ball and the object ball head off in their respective directions at the same speed. For this reason, the half-ball hit is most commonly used for safeties -- both for cue ball / object ball hiding safeties, as well as pinning-the-object-ball-to-an-adjoining-rail-to-force-your-opponent-into-a-bankshot safeties. This property, of course, goes out the window on barboxes with non-standard (e.g. heavy) cue balls.

3. Many effective aiming systems are based on first sighting a half-ball hit (e.g. CTE), so it's a well-known "first step" ball-to-ball relationship.

4. The half-ball hit is the one shot that most prominently displays the effects of spin-throw (spin/throw effects are optimum during a half-ball hit), so if you can master spin with a half-ball hit, other ball-cut angles are a piece of cake.

5. A half-ball hit shot optimizes the chance for a skid -- most complaints e.g. "that ball skidded on me!" occur during, or close to, a half-ball hit angle.

Good thread, and I'm sure some really interesting posts are going to be contributed!
-Sean
 
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This is why the hb hit has been known for generations to be the foundation of english billiards. No other way of making a run consisting of hundreds of scratches on a 12' table with 4" pockets.
 
Another fun fact about half ball hits that I have found useful in safety play is that the cue ball and object ball travel the same distance after a half ball hit.
 
Luxury said:
Another fun fact about half ball hits that I have found useful in safety play is that the cue ball and object ball travel the same distance after a half ball hit.
Click to expand...

That's what I said in point #2 in post #2 above. ;)

But yes, it does bear reinforcing, for damn sure! That actually should be point #1 instead of #2.

-Sean
 
Luxury said:
Another fun fact about half ball hits that I have found useful in safety play is that the cue ball and object ball travel the same distance after a half ball hit.
Click to expand...

This bears repeating. This fact can be used to take a lot of the "touch" (speed control, really) out of certain safety shots.

-Andrew
 
sfleinen said:
That's what I said in point #2 in post #2 above. ;)

But yes, it does bear reinforcing, for damn sure! That actually should be point #1 instead of #2.

-Sean
Click to expand...

Apparently the fact that it bears repeating... bears repeating.

Oh well, it's the sincerest form of flattery, right Sean?

-Andrew
 
Andrew Manning said:
Apparently the fact that it bears repeating... bears repeating.

Oh well, it's the sincerest form of flattery, right Sean?

-Andrew
Click to expand...

*coffee spit all over monitor*

Thanks, Andrew. Now I have to go find a paper towel...

:D
-Sean
 
nrhoades said:
I was looking at some of Dr. Dave's proofs and noticed something interesting. I'm sure that most of you know about this, but at least myself and one of my friends didn't, so I'll share.
Click to expand...
Good illustrations!

There are many "gems" associate with the 1/2-ball hit. Mike Page has an excellent summary here:
and Bob Jewett has an excellent article on this topic here:

and the following video demonstrates the powerful implications of the 30-degree rule:

FYI, more information, articles, and videos on this topic can be found here:

Regards,
Dave
 
dr_dave said:
Good illustrations!

There are many "gems" associate with the 1/2-ball hit. Mike Page has an excellent summary here:
and Bob Jewett has an excellent article on this topic here:

and the following video demonstrates the powerful implications of the 30-degree rule:

FYI, more information, articles, and videos on this topic can be found here:

Regards,
Dave
Click to expand...


Wow. Thanks! I have to learn to read the existing literature first before making my own.
 
and......whenever I get stuck trying to aim a bank shot, or it doesn't feel right, I go with the 1/2 ball hit, and more likely then not it goes.

Funny thing....I had a post over at 1p.org about banking. John Brumback pm'd me to start with 1/2 ball hit and start adjusting from there!

G.
 
Gerry said:
and......whenever I get stuck trying to aim a bank shot, or it doesn't feel right, I go with the 1/2 ball hit, and more likely then not it goes.

Funny thing....I had a post over at 1p.org about banking. John Brumback pm'd me to start with 1/2 ball hit and start adjusting from there!

G.
Click to expand...

I showed this to my friend Chris who is a much better player than me about 7 years ago and he couldn't believe it. I told him aim for a half-ball hit when the ball is close to the rail and sure enough the banks go in.

Or maybe he showed it to me.....anyway we spent about an hour trying it out and were both convinced that it's a good way to aim banks.

Here is something else to try. When shooting to make a ball in the side aim at the half ball and get down and shoot. See what happens. I think you might be surprised at the number of angles you can make the object ball go cleanly into the side from the half-ball approach.

For the PURISTS and the SCIENTISTS - no, a TRUE half-ball hit does not work for all shot angles to the side. BUT for some reason it works for a large number of angles when the shooter starts by looking at the half-ball hit and then goes into the shot and shoots.

optical illusion? subconscious? Who knows? But this was discovered by a pair of C-players in Loveland Colorado during a weekly tournament after I showed them some other aiming methods. I tried it and it worked. And it works well enough that I have won drinks setting up some pretty hairy cuts to the side and using that approach.
 
Question: What's the difference between a 1/2 ball Hit and a 1/2 ball Aim?
randyg
 
randyg said:
Question: What's the difference between a 1/2 ball Hit and a 1/2 ball Aim?
Click to expand...
If you aim to send the center of the CB through the edge of the OB (i.e., along the CTE line), then you are visualizing a "1/2-ball aim." A "1/2-ball hit" is what you get when you sight and align the cue along the desired line and deliver the stroke reliably with the desired tip contact point to actually send the CB to the necessary ghost-ball position to create at 30-degree cut angle (a 1/2-ball hit).

Or are you implying something else?

Regards,
Dave
 
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JB Cases said:
I showed this to my friend Chris who is a much better player than me about 7 years ago and he couldn't believe it. I told him aim for a half-ball hit when the ball is close to the rail and sure enough the banks go in.

Or maybe he showed it to me.....anyway we spent about an hour trying it out and were both convinced that it's a good way to aim banks.

Here is something else to try. When shooting to make a ball in the side aim at the half ball and get down and shoot. See what happens. I think you might be surprised at the number of angles you can make the object ball go cleanly into the side from the half-ball approach.

For the PURISTS and the SCIENTISTS - no, a TRUE half-ball hit does not work for all shot angles to the side. BUT for some reason it works for a large number of angles when the shooter starts by looking at the half-ball hit and then goes into the shot and shoots.

optical illusion? subconscious? Who knows? But this was discovered by a pair of C-players in Loveland Colorado during a weekly tournament after I showed them some other aiming methods. I tried it and it worked. And it works well enough that I have won drinks setting up some pretty hairy cuts to the side and using that approach.
Click to expand...

The CTEL is a beautiful thing.
 
randyg said:
Question: What's the difference between a 1/2 ball Hit and a 1/2 ball Aim?
randyg
Click to expand...

Oh, I can't resist...

"One is the result of the other?" (The former is the result of the latter?)

:p

J/K,
-Sean
 
sfleinen said:
2. The path of the object ball and the cue ball, as well as their SPEED, is very predictable. In fact, on a table with a normal cue ball (i.e. same size and mass as the object balls themselves), a half-ball hit results in the cue ball losing 50% of its kinetic energy, and the object ball inheriting that 50% kinetic energy. Result? The cue ball and the object ball head off in their respective directions at the same speed.
Click to expand...
That's true for 45-degree cut with stun on the cueball (no top or bottom spin). With a 30-degree cut, immediately after impact the object ball inherits (nice term) 75% of the cueball's energy, while the cueball retains 25%. Their respective speeds are 87% and 50% of the CB's pre-impact velocity. If the cueball is rolling before impact, however, their speeds equalize after natural roll sets in for both balls (i.e., the OB slows down some while the CB speeds up).

sfleinen said:
3. Many effective aiming systems are based on first sighting a half-ball hit (e.g. CTE), so it's a well-known "first step" ball-to-ball relationship.
Click to expand...
That's debatable. :)


sfleinen said:
4. The half-ball hit is the one shot that most prominently displays the effects of spin-throw (spin/throw effects are optimum during a half-ball hit), so if you can master spin with a half-ball hit, other ball-cut angles are a piece of cake.
Click to expand...
Not sure what you mean? Throw due to spin can be just as great at any cut angle.

sfleinen said:
5. A half-ball hit shot optimizes the chance for a skid -- most complaints e.g. "that ball skidded on me!" occur during, or close to, a half-ball hit angle.
Click to expand...
Not really, if by skid, you mean abnormal amounts of throw arising from surface contamination. Normal throw is typically maximized in the 20-40 degree range for stun shots, which might be interpreted as 'skid.'

Sorry about the nitpicking.

Jim
 
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