OB Throw Video for the Physics Nerds

MacGyver said:

Just wondering, but which angle was the "true" cut angle at?

I mean discounting throw/english at all and just the line between each balls center at moment of contact...

Click to expand...

I actually had a small arrow piece of paper indicating what I believe to be the true cut angle (line through ball centers), but it doesn't show up well on the video.

It's actually about where you see the OB hit on the hard shots. Perhaps an inch or so left of that point.

btw: One degree works out at about 1.5 inches. So for the hard shots, they are about 1 degree short of the natural cut angle as I figure.

General Note:
I think this test indicates that alignment with natural roll, draw, hard shots and Inside English (on over 15 degree cuts) is very predicatable. But soft stun and outside english bring in large variations that require adaptation and fine touch for consistancy.

1/4 and 3/4

MacGyver said:

Very very cool stuff...

I'd like to see the same done for a thinner hit or a fuller hit(1/4 and 3/4 perhaps), I wonder how they compare to 1/2 ball hits.

Click to expand...

I figure the results will be pretty similar with 1/4 and 3/4 angles, though the range may squeeze up a bit on the ends. Also, as we move toward full ball, IE starts to act a bit differently and begins throwing the OB toward the direction of the spin, which it seems not to do at 20 degrees and finer cuts.

All very crucial data for making sense of BHE type systems.

I'll do a bit more testing on thicker and thinner cuts. Not sure if I will do a whole new video though...takes a few hours.

frankncali said:

I just wonder how "off line" your stroke was. Not trying to put you down but it looked like an aweful lot of movement on some of the shots.

Did you do the test on straight ahead full ball hits as well?

I was surprised by the fact that inside english had little effect on the OB compared to the outside and stun. The first shot (i believe) had the most effect on the OB to the shooters left. I would have thought that
a slow inside english shot would have had the most in this direction especially considering the shooting angle.

If you make some more please post them as they are interesting to view.
I think it you could shoot the same shots with different cues(shafts) it
would be interesting. I just wish the stroke was more mechanical.

nice stuff thanks

Click to expand...

Hi Frank,
Part of the cue movement you saw may have been caused by exagerating the cue movement after contact to avoid the double kiss as the CB and OB are just an inch apart.

On each shot I line up quite precisely with the butt on the pocket edge and an aim point on the side rail. I also bridge at the pivot point so that any error in where the CB contacts the OB is very small...I believe much less significant than speed and secondly the amount of spin.

I've tested these angles quite a lot and get consistant results. But as I mentioned, on the stun shot the speed can have quite an influence. On the OE shots, the amount of spin applied makes a significant difference.

The other shots are fairly consistant, rarely varying more than an inch either side.

The 2 balls are held in small dimples made by tapping them into spot before the tests.

It may not be highly robotic, but it is repeatable and can confirm the basic relationships of CIT (Contact Induced Throw) and SIT (Spin Induced Throw) effects.

The video is just a demonstration which selected the shots that performed according to past testing. Most of them came out perfect first shot. Some I had to hit a few times to get the speed or spin right so that they hit the markers which represents the average test result.

eg. The slow stun will often travel thinner if you hit it a bit harder or get a little spin on it. And the OE shots can vary a few inches depending on how much spin I get on the CB and how it grips the OB.

MacGyver said:

I'm not suprised about inside...

remember with a cut you have CIT which is acting as outside english due to the gear motion when the balls collide.

Thus any extra outside would be able to magnify the throw, while inside would have to counteract the CIT and THEN work to throw the ball.

a bit(only in analogy) like jumping up the same strength in an elevator that stopping downward or stopping upward. Same amount of force involved in jump but acting together produces much bigger reaction than against.

Click to expand...

What I think is happening with IE is that the spin increases the speed between the contact surfaces and that this reduces friction and hence throw.

Hitting with IE basically has the exact same throw effect as hitting with follow (for cut angles 15 degrees or more) making it a quite predictable shot for using Back Hand English so long as you know your cue's pivot point for the speed of shot being played.

I'll rarely miss a BHE shot with IE so long as the distance is not so great, or the speed not too slow such that swerve comes into play.

However, with BHE using OE, I have to aim the original pot line to miss by a few degrees to make the shot, or use a bridge much longer than the pivot point to get a thicker contact, or play the shot much harder which increases the squirt for a thicker contact and reduces the SIT slightly. All these still tend to make the shot less predictable and less consistant without a lot more practice.

One lesson to consider from this is that it may not be a good idea to practice with a lot of stun shots as it will program your brain to line up to overcut the angle shots when played with increased speed or roll or harder follow or draw.

To me the best way to drill the pot angles into the brain is to play a lot of of medium speed natural roll potting (which pots within a degree of hard shots, draw or follow, slow roll and IE shots. Then adjust as necessary when you need to play soft stun (aim thinner) or OE (aim thicker).

A lot of people fall into the habit of playing some OE on many of their shots. From this testing, it would not seem to be a good idea for both consistancy and memorizing the pot angle considerations. That said, there is an argument to be made for playing stun shots with a touch of OE to bring the pot angle to the same as the medium speed roll potting angle. A lot of players seem to do this intuitively, but it requires good feel and accuracy of CB hit. Just an 1/8th tip too much or too little OE can widen or narrow the pot angle significantly.

UWPoolGod1 said:

HAve you guys ever been here for slow motion collision videos? Check them out. They are very educational. There is also a large section on the physics of pool.
http://www.engr.colostate.edu/~dga/pool/index.html

Click to expand...

Yep, many times. It a great resource and some of the work done by Dr. Dave is the reason I created the video so as to make a more visually clear demonstration of some of theories he and others have discussed.

frankncali said:

Thanks for the response

I read your response to McGyver and understand what you are saying. Just in my thinking I would have figured that the CIT would have started
the OB pushing and then the IE would have increased it. I guess not.

Click to expand...

That's what I had imagined would happen, but some early testing showed it just wasn't the case on cut angles. I had been playing with some BHE adjustment systems and it just wasn't working as expected with IE cut shots. So I think this knowledge is very useful for anyone wanted to take a more systematic approach to adjustment.

Also, the soft stun creating the very large amounts of throw surprised me a bit, and explained a lot of confusion I had encountered over the years where I would sway back and forth between undercutting stun shots to overcutting the other shots based on what I was perceiving as the 'correct' potting angle. Now I know that there this correct angle (or contact point) varies more than I had thought and so I need to adjust my methodology of pot angle adjustment to better fit with what is really going on.

Years ago a guy showed me a shot that demonstrated just how much
an OB could be thrown off target by the shooters hitting unwanted english on the cueball. A lot of people do not believe this or dont realize it until they are shown.
That shot was a straight on hit. I like seeing the results you have gotten
on shots with a cut angle. .

Click to expand...

Yes, from a touching ball, the line can be thrown off a few degrees in either direction using either english (cueing straightish) or soft stun (across the ball).
On straightish shots, either spin left or right will act similar to how we see the OE acting in the video, turning the OB significantly. So any slight pull or push across or hitting slightly off center will have a significant effect. One way to reduce this is to hit it harder. This reduces the throw, but it may cause greater cueing inaccuracy too.

Watching alot of good players I notice them spinning the balls often. Thats one huge difference between bangers and Pros. The Pros have the ability to control the balls better with the english applied. They also have an ability to hit most any shot with most any english and get the wanted results.

Do you think that the Pros make an actual adjustment physically or that they just "know" what needs to happen and it occurs? Its hard enough to
find "the spots" without making tiny adjustments IMO

Click to expand...

I doubt many pro-players really understand this in all its details. Instead, they learn to memorize a wide range of shots and how to align to them.

Doing it that way, you need to keep in mind during the alignment what speed and spin you will be applying and then search the feel database. In my own experience the brain sends a message such that 'on this shot I tend to aim too straight...adjust thinner' based on past misses and successes.

But I think this is a slow and awkward process and requires immense memorization and familiarity with many shot types.

I expect that someone who can use an alignment system based on the real physics aspects as noted above, can quickly become highly proficient in finding the pot angles for the medium speed follow shot, and then make pretty accurate adjustments based on that angle such that a pretty full range of shots become consistantly executable and better yet, understandable (so that intellegent adjustments can be fine tuned).

There will always going to be a range of shots that require lots of practice and intuitive adjustment based only partly on an understanding of the physics knowledge such as masse, swerve, drag shots, CB positioning and how all those vary according to cloth and cushion conditions.

Funny thing is how many bangers I've seen who can pot the lights out. They achieve this by hitting most shots on the CB in the same place (usually just above center) and similar speed on nearly every shot. It's when players start trying to control the CB and table planning better with varying spins and speeds that their potting confidence starts going down the drain.

So I think this knowledge, combined with a knowledge of your cue's pivot point characteristics for applying BHE can allow an average banger to quickly step up to the next level of play.

And it may even allow an advanced player to improve their consistancy on some of their problem shots.

Note: One thing I didn't show in the video, or mention is the OE when played hard also straightens back toward where the other hard shots go. Here again the increased speed between surfaces reduces the effect of spin in inducing throw.

jsp said:

Thanks for the video and data Calc.

From your data, I guess I was wrong when I mentioned in the previous thread that a slow roll follow would accentuate the effects of throw (compared to a stun shot). Jal, you're right once again.

It's also interest to see the very predictable results using inside english. I remember reading a thread in the CCB forum. A poster stated that Efren uses low, inside english on the CB to reduce the chances of kicks/skids. Many posters (myself included) thought that what he meant to say was outside english instead of inside english. But from your data, maybe he was correct all along saying the Efren uses inside english.

Click to expand...

Some of the stuff Jal was talking about also helped me to get a better understanding of this. Thanks Jal!

That's interesting about Efren. Since making the discovery that IE OB angles behave almost identically to follow, I've been having a blast playing a lot of shots with IE with aim and pivot that previously were quite intimidating. On most shots my potting consistancy is similar to what it is potting with natural roll...and that is getting better the more I practice potting with natural roll.

The only times using IE gets tricky (requires additional adjustment) using pivot and aim (BHE) is the following:

1. On soft shots - the squirt reduces considerably and swerve comes into play, so I have to aim to overcut a little.

2. On long shots - These get tricky unless you have a very good understanding of your cue's pivot point for the speed you are playing the shot. Just a small error over 6 or so feet makes the CB hit at a distance from the required contact point.

3. On straightish slow and medium speed shots - the OB will turn noticeably, so again I have to aim to overcut a bit before pivoting.

4. Shooting very hard - This wil increase the squirt, but I can adjust to this quite well by shortening by bridge length to about 8-10 inches for high speed execution. (My normal low to medium speed pivot point is about 14")

Billy_Bob said:

Wow! This is great stuff - helps me to visualize throw and different hits. Certainly explains my troubles with power draw shots.

This is the best post of the year in my opinion.

Thanks!

Click to expand...

You're welcome BB. Glad you got something out of it.

I'm planning to do a lot more videos to clearly demonstrate some of the more advanced concepts of the game and also some of my methodolgies for using systems.

I will put them into a book or (pdf) with more detailed commentary and explanation and accompanying video links or DVD at a future date.