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View Full Version : spin transfer & "vertical throw" from follow/draw



dr_dave
05-30-2007, 05:05 PM
FYI, I just filmed and posted some high-speed video clips that illustrate spin transfer and "vertical throw" (ball hop) resulting from follow and draw. The clips can be found in HSV A.143-A.146 (http://www.engr.colostate.edu/~dga/pool/high_speed_videos/index.html). Notice how the effects are much greater when chalk is added to the object ball surface.

Remember: keep those balls clean.

Regards,
Dave

cushioncrawler
05-31-2007, 07:06 PM
Dr Dave -- Nice slo-mo's. I am allways amazed at how little the qball stuns-throo the OB at impakt, for pool balls, the "e" must be about 0.97 or something. In the slo-mo's the qball actually bounces back a little during impakt, ie az if "e" is 1.03 or something, even for the "chalky" impakts. I think that the qball here must have been much lighter than the OB. madMac.

dr_dave
06-01-2007, 09:55 AM
<blockquote><font class="small">Quote cushioncrawler:</font><hr> Dr Dave -- Nice slo-mo's. I am allways amazed at how little the qball stuns-throo the OB at impakt, for pool balls, the "e" must be about 0.97 or something. In the slo-mo's the qball actually bounces back a little during impakt, ie az if "e" is 1.03 or something, even for the "chalky" impakts. I think that the qball here must have been much lighter than the OB.<hr /></blockquote>Mac,

I used a brand new set of Elephant Practice Balls for these clips. I would be very surprised in the cue ball were "much lighter" than the object ball. I'll weight them when I can get access to high-quality digital scale. If the weights are different, I bet the difference is only a tiny fraction.

I just played HSV A.143 (http://www.engr.colostate.edu/~dga/pool/high_speed_videos/new/HSVA-143.htm) on my computer, placing the cursor at the ball impact point. The cue ball seems to stop pretty much perfectly in place at impact (i.e., the cue ball pretty much stays on the cursor), before the follow does its thing. The cue ball bounces back only a hair. I agree with you that the COR (e) must be pretty good.

Regards,
Dave

dr_dave
06-01-2007, 10:35 AM
<blockquote><font class="small">Quote cushioncrawler:</font><hr> Dr Dave -- Nice slo-mo's. I am allways amazed at how little the qball stuns-throo the OB at impakt, for pool balls, the "e" must be about 0.97 or something. In the slo-mo's the qball actually bounces back a little during impakt, ie az if "e" is 1.03 or something, even for the "chalky" impakts. I think that the qball here must have been much lighter than the OB.<hr /></blockquote>Mac,

FYI, I just took some measurements and did some calculations from HSV A.143 (http://www.engr.colostate.edu/~dga/pool/high_speed_videos/new/HSVA-143_follow-shot_no-chalk-on-ball.wmv), based on the incoming cue ball speed and the outgoing object ball speed. I calculated a coefficient of resitution (AKA "COR" or "e") of 0.95, so the cue ball must be a hair lighter to stop in place (or bounce back a hair).

Regards,
Dave

cushioncrawler
06-01-2007, 04:46 PM
Dr Dave -- I carry a small digital set of scales in my cue case at all times. Cost me $104. I find that english billiards balls fall between 137.0gm and 142.5gm. In a set of three, they are supposed to be all within 3gm of each other, which is a terrible rule, in the oldendayz the rule used to say "within 0.3gm". Anyhow, 3gm in 140gm is about a 2% varyation, which might make an e of say 0.96 act like an e of 0.94 or 0.98 (nearnuff). Elephant balls have a reputation i think for accuracy of diameter etc, but u never know. madMac.

dr_dave
06-02-2007, 07:54 AM
<blockquote><font class="small">Quote cushioncrawler:</font><hr> Dr Dave -- I carry a small digital set of scales in my cue case at all times. Cost me $104. I find that english billiards balls fall between 137.0gm and 142.5gm. In a set of three, they are supposed to be all within 3gm of each other, which is a terrible rule, in the oldendayz the rule used to say "within 0.3gm". Anyhow, 3gm in 140gm is about a 2% varyation, which might make an e of say 0.96 act like an e of 0.94 or 0.98 (nearnuff). Elephant balls have a reputation i think for accuracy of diameter etc, but u never know. madMac.<hr /></blockquote>Mac,

I don't have a high quality scale handy, but I do have a Vernier Caliper. I just checked the diameters of my new Elephant Practice Balls. There is a slight difference. The CB measured 2.249" and the OB measured 2.255". Assuming uniform and consistent density, these diameters would imply the OB is about 0.8% heavier than the CB. That would explain why the cue ball stopped dead (or even backed up a hair) in the videos, as you observed. The lighter weight of the CB is counteracting the COR (e) effect.

Regards,
Dave

cushioncrawler
06-02-2007, 07:37 PM
Yes -- 0.8% is about 1.3gm in 160gm, pretty good -- a 4.0gm diff would mean trouble. In oldish snooker sets the white is often as much as 5gm light (in 140gm) due to wear, and this badly affects snooker play, ie the qball runthroo velocity, and qball deflexion angle, but i guess that it duznt affect the OB angle much -- and it is poizon for english billiards, ie for loozers, ie for the in-off angle. madMac.