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View Full Version : A measurement of SIT

Ross
12-09-2004, 12:08 AM
Ok, we had a thread arguing that spin induced throw is indeed real. In Dave's Q&amp;A he states (like many others before him) that SIT exists, and gives some mathematical equations to describe it. The next step is to quantify it for real life situations. That is, how far is the ob thrown for different side english shots?

The problem in testing this is to make sure you are hitting the ob where you think you are. Because of both swerve and stroke variation you may think you threw the ball when in reality you just cut the ob because you hit it in a different place than you thought.

So to make sure any deviation in the cb path from the line of centers was due to SIT and not due to cutting the ball I set up the following test (balls were fairly new Super Arimith balls, average cleanliness for a home table):

START(%A^7Z7%B`1Z7%C]4Y3%DQ7[0%E]5Z7%Fa5Z7%GF3Y4%HF3V3%IF3Z8%Pa4Y4
%WD4X0%X\2Y3%]L2W0%^C4W8%eA6a7)END

This setup made ensured that I hit the ob either exactly in the center or more likely very, very slightly to the right of center (opposite direction of the throw). Otherwise I ran into one of the blocking balls between the cb and ob. Oh yeah - I removed the 5 next to the ob before I shot.

Results:

When the cb was 2 balls away from the ob (4 1/2 inches), using max left english, soft shot (just enough to make it to end rail and back less than 2 diamonds), the ob usually missed both balls frozen close to the corner pocket by about 1/4 to 3/4 inch. To miss the 7 the ob had to be thrown a balls width or 2 1/4 inches. Once out of 15 or so tries I hit the 8 ball directly. Since it was 1 1/2 balls away from the 7, this indicated a throw of 1 1/2 balls or 3 3/8 inches.

Bottom line: For a straight on hit with the ob about 4 or 5 inches away and a target about 4 diamonds away, a very slow hit with nearly maximum side english will throw the ball a little more than a balls width (or about 2 1/2 to 3 inches).

Variations:

I got about a 1/4 to 1/2 inch more throw (maybe 2 3/4 to 3 1/2 inch total on average) when I moved the cb to within 1 ball of the ob.

When I moved to cb to a distance of 3 balls (6 3/4") it was more difficult to hit the ob exactly where I wanted. In other words the swerve toward the blockers was harder to judge for these soft shots. In any case typically the ob hit the 7 indicating a throw consistently less than 2 1/4 inches.

Back to the 2 ball gap but with a different speed: When I hit the ball a little harder (enough to get a 4 diamond rebound to the middle of the table) the ob often clipped the 7 ball, meaning the throw was typically about 2 inches or so.

PS - The 4 ball is there to save effort. Occasionally I would clip the blocking balls (the 1 and 2) and this would cut the ob toward the corner pocket messing up my measuring setup next to the corner pocket. So I put another blocking ball half way to the pocket to intercept the errant little bugger.

This experiment just takes a minute to set up. Anyone else willing to try it on their table and report the results to see how much variation there is due to cloth, balls, etc.?

Bob_Jewett
12-09-2004, 11:06 AM
<blockquote><font class="small">Quote Ross:</font><hr>...

This experiment just takes a minute to set up. Anyone else willing to try it on their table and report the results to see how much variation there is due to cloth, balls, etc.?
<hr /></blockquote>
I think the experiment at http://www.sfbilliards.com/throwtest.gif that I suggested before is much easier to set up and has much better control to prevent the shooter from making subconscious corrections.

I think your result is correct for clean balls. I think you can get almost as much throw with less english as long as the cue ball doesn't have any draw or follow when it gets to the object ball.

Ross
12-09-2004, 11:53 AM
Bob, your setup and test (both ob and cb go to the left) seem more designed to prove the existence of throw than to measure it's effects.

Our setups are very similar but I have a measuring device at the end (for example you can just look at how far you miss the 7 and add that to 2 1/4" to estimate your throw. Or if you hit the 8 you know you are getting 3 3/8" throw or more).

Also in your setup the only way to be sure you didn't actually cut the ob to the left is if the cb doesn't move at all to the right. This determination in turn (for the most accurate head-on hits) requires some judgement or using a ball to measure the distance of the cb from the rail. My setup automatically ensures that you cannot cut the ball toward the direction of the throw.

So either setup would work for determining the size of the throw effect. You would just have to add a target for yours and make sure the cb never drifted to the right at all.

Bob_Jewett
12-09-2004, 12:05 PM
<blockquote><font class="small">Quote Ross:</font><hr> Bob, your setup and test (both ob and cb go to the left) seem more designed to prove the existence of throw than to measure it's effects.
<hr /></blockquote>
Well, mostly, but the final measurement in my setup is how far the cue ball can be from the object ball and still move the object ball to the side but keep the cue ball from moving to the opposite side. I think that many players over-estimate this distance.

Fred Agnir
12-09-2004, 12:33 PM
<blockquote><font class="small">Quote Ross:</font><hr> Results:

When the cb was 2 balls away from the ob (4 1/2 inches), using max left english, soft shot (just enough to make it to end rail and back less than 2 diamonds), the ob usually missed both balls frozen close to the corner pocket by about 1/4 to 3/4 inch. To miss the 7 the ob had to be thrown a balls width or 2 1/4 inches. Once out of 15 or so tries I hit the 8 ball directly. Since it was 1 1/2 balls away from the 7, this indicated a throw of 1 1/2 balls or 3 3/8 inches.

Bottom line: For a straight on hit with the ob about 4 or 5 inches away and a target about 4 diamonds away, a very slow hit with nearly maximum side english will throw the ball a little more than a balls width (or about 2 1/2 to 3 inches).
<hr /></blockquote>Good experiment and demo, Ross. I think if everyone tried it, they see just how much of these shots are due to throw and how much is due to swerve (by implication of the difficulty of missing the blocking balls).

It's very interesting (and not surprising) what happens when you either increase the speed of the shot (and not much) or increase the distance. The "increases" start to mimic most speeds and distances of shots, shots that people continue to say that they "throw" or "spin in."

Fred