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calcuttaman
02-08-2007, 12:25 PM
Lets say you had a straight in shot, and you hit the cue ball just ever so slightly above center.

Would the cue ball "bounce back" somewhat then continue slightly forward?

Same situation but with definate top english. Is there any "bounce back" to the cue ball?

bsmutz
02-08-2007, 01:00 PM
I'll leave it to the physics experts to put this to rest; but my guess would be that it wouldn't bounce back, but hesitate/stop before rolling forward. I think the mass that the cue ball is hitting needs to be more than that of the cue ball to cause backward motion before rolling forward.

randyg
02-08-2007, 01:49 PM
<blockquote><font class="small">Quote bsmutz:</font><hr> I'll leave it to the physics experts to put this to rest; but my guess would be that it wouldn't bounce back, but hesitate/stop before rolling forward. I think the mass that the cue ball is hitting needs to be more than that of the cue ball to cause backward motion before rolling forward. <hr /></blockquote>

Great answer...randyg

Jal
02-08-2007, 02:21 PM
<blockquote><font class="small">Quote calcuttaman:</font><hr> Lets say you had a straight in shot, and you hit the cue ball just ever so slightly above center.

Would the cue ball "bounce back" somewhat then continue slightly forward?

Same situation but with definate top english. Is there any "bounce back" to the cue ball? <hr /></blockquote>What bsmutz said. It doesn't really matter how much topspin you put on it. If the masses of the two balls are the same, the cueball should stop for a moment.

In reality though, it moves forward slightly because the collision isn't perfectly elastic. But since cueballs wear down faster than the other balls, I suppose it's often true that it does either stop or bounce back a little, the inelasticity of the collision being balanced by its lower mass, more or less.

Jim

cushioncrawler
02-09-2007, 12:24 AM
Jim -- From some tests i did on small balls, the qball allways follows throo (for a fullball impact) at a speed that depends on "e". This varyd from 2.8% of its original speed for a low speed impact of 1m/s, and woz 4.7% for 6m/s. This is the qball's remaining speed at the end of impact. It duznt matter whether the qball has draw or top or stun -- these effects only come into play in the seconds after impact ends.

During impact, my newton shmoos told me, that the qball moovs forward (while it is in contact with the objectball) about 0.2mm at 1m/s, and about 1.2mm at 6m/s. Here, the qball is slowing down from its initial approach speed to its "final speed". madMac.

Jal
02-09-2007, 04:46 PM
<blockquote><font class="small">Quote cushioncrawler:</font><hr> Jim -- From some tests i did on small balls, the qball allways follows throo (for a fullball impact) at a speed that depends on "e". This varyd from 2.8% of its original speed for a low speed impact of 1m/s, and woz 4.7% for 6m/s. This is the qball's remaining speed at the end of impact. It duznt matter whether the qball has draw or top or stun -- these effects only come into play in the seconds after impact ends.

During impact, my newton shmoos told me, that the qball moovs forward (while it is in contact with the objectball) about 0.2mm at 1m/s, and about 1.2mm at 6m/s. Here, the qball is slowing down from its initial approach speed to its "final speed". madMac. <hr /></blockquote>Hi Mac. I thought you would have something to say about this since you've done testing in this area. Your results (.2mm at 1m/s and 1.2mm at 6m/s) are consistent with a contact time of .0004 seconds, as opposed to Marlow's measured value of .0002. I know you don't hold Hertz's theory in much regard, so are you using some other method to get the force, other than F ~ x^(3/2), where x is the total compression distance? Why do you think the .0004 might be/is more accurate?

Jim

cushioncrawler
02-09-2007, 05:47 PM
<blockquote><font class="small">Quote Jal:</font><hr> <blockquote><font class="small">Quote cushioncrawler:</font><hr> Jim -- From some tests i did on small balls, the qball allways follows throo (for a fullball impact) at a speed that depends on "e". This varyd from 2.8% of its original speed for a low speed impact of 1m/s, and woz 4.7% for 6m/s. This is the qball's remaining speed at the end of impact. It duznt matter whether the qball has draw or top or stun -- these effects only come into play in the seconds after impact ends.

During impact, my newton shmoos told me, that the qball moovs forward (while it is in contact with the objectball) about 0.2mm at 1m/s, and about 1.2mm at 6m/s. Here, the qball is slowing down from its initial approach speed to its "final speed". madMac. <hr /></blockquote>Hi Mac. I thought you would have something to say about this since you've done testing in this area. Your results (.2mm at 1m/s and 1.2mm at 6m/s) are consistent with a contact time of .0004 seconds, as opposed to Marlow's measured value of .0002. I know you don't hold Hertz's theory in much regard, so are you using some other method to get the force, other than F ~ x^(3/2), where x is the total compression distance? Why do you think the .0004 might be/is more accurate? Jim <hr /></blockquote> Jim -- I did some of my tests on cheap soft light pool balls, "e" here would be perhaps 0.92 instead of perhaps 0.95 for the best pool balls. I calculated the impact times to be 0.00040 at 0.9m/s and 0.00036sec at 6m/s. So, i would give way to any actually measured impact times, especially for good balls. And my calcs rely heavily on my tests for flatspot dia versus load, using a static load (me and my ford), so here again, my results using static forces shood give way to actual impact times which involve dynamic short-term forces. It was better than nothing, at that time. madMac.

kyle
02-11-2007, 03:38 PM
I think the hesitation is the cue ball sliding before the high gear takes affect.

cushioncrawler
02-14-2007, 01:04 AM
<blockquote><font class="small">Quote calcuttaman:</font><hr> Lets say you had a straight in shot, and you hit the cue ball just ever so slightly above center. Would the cue ball "bounce back" somewhat then continue slightly forward? Same situation but with definate top english. Is there any "bounce back" to the cue ball? <hr /></blockquote> I just revizited Dr Dave's videos of frozen throw. U karnt see the qball, but u can see both object balls. Most of the impacts are done at 2 or even 3 speeds. Anyhow, if u look, u can see the No1 ball stunning throo the No2 ball faster and faster as the speed increases. This is due to "e" being less than 1.00. But it can allso be inkreeced by a heavy No1 ball. madMac.

calcuttaman
02-14-2007, 06:05 AM
<blockquote><font class="small">Quote cushioncrawler:</font><hr> I just revizited Dr Dave's videos of frozen throw. U karnt see the qball, but u can see both object balls. Most of the impacts are done at 2 or even 3 speeds. Anyhow, if u look, u can see the No1 ball stunning throo the No2 ball faster and faster as the speed increases. This is due to "e" being less than 1.00. But it can allso be inkreeced by a heavy No1 ball. madMac. <hr /></blockquote>

Exactly what videos numbers are you viewing. I did look at some of his "frozen" ball video's but if anything, those are 2 different situations, ie, I'm only talking about bounce back on a single object ball where it looks like there might be some bounceback on 2 frozen object balls in the videos (and it looks like they use a stun shot).

cushioncrawler
02-14-2007, 04:06 PM
<blockquote><font class="small">Quote calcuttaman:</font><hr> <blockquote><font class="small">Quote cushioncrawler:</font><hr> I just revizited Dr Dave's videos of frozen throw. U karnt see the qball, but u can see both object balls. Most of the impacts are done at 2 or even 3 speeds. Anyhow, if u look, u can see the No1 ball stunning throo the No2 ball faster and faster as the speed increases. This is due to "e" being less than 1.00. But it can allso be inkreeced by a heavy No1 ball. <hr /></blockquote> Exactly what videos numbers are you viewing. I did look at some of his "frozen" ball video's but if anything, those are 2 different situations, ie, I'm only talking about bounce back on a single object ball where it looks like there might be some bounceback on 2 frozen object balls in the videos (and it looks like they use a stun shot). <hr /></blockquote> I think that the videos are A-86 etc. Its a pity that the qball iznt shown, koz i am sure that it would be seen to bounce-back (at first) no matter what spin or top it had -- here the qball feels all of the mass of the first-ball and a large bit of the mass of the second-ball, ie the first-ball would feel very heavy, hence the bounce-back.

But i didnt mention these videos re the possible (but unfortunately invisible) qball bounce-back here, i mentioned them koz they might be more convincing to some players out there. What i mean, is, the first-ball is here more likely to have pure stun, and hence there shood be less room for arguement that a bit of topspin is fooling everyone.

Hmmmm -- Wait, i have changed my mind. Yes, i am (partly) wrong. If the first-ball (in the frozen combo) feels heavyr to the qball, then the qball must feel heavy to the first-ball allso, hence u shood expect quite a large stun-throo effect, ie making it look like "e" was smaller, eg say 0.90 instead of say 0.95). Ok, disregard everything i said.

madMac and madSherie went for a longish drive this week to see a guy at a timber mill at a small town. Afterwards we had a counter-dinner at the pub (a one-pub town). They had a 7' bar table, nice blue cloth, and the local pub team, with their team-shirts, were warming up for their 8-ball match against the team from a pub in another town. Got talking to one guy, turned out to be the brother of one of my old team mates who happens to live on the same hill as me (my mountain home the other side of Melbourne). Got talking to the barman (the owner), he told me that some time ago he played a few frames of snooker against the then Prime Minister of Ozz, at their club in Melbourne, i bet that no-one here can say they ever took money off the Prez of the USA. Anyhow, the qball on the blue bar-table was small n lite, and of course bounces back (at first) on every shot. madMac.

Qtec
02-14-2007, 10:26 PM
There might be a bounce up. There could be a bounce forward. Bounce back- ball on ball? Don't think so.

Q

TennesseeJoe
02-18-2007, 06:36 PM
There is another factor which could have an impact on your conclusions. When a cue tip contacts a cue ball, the cue ball usually elevates and the faster it is hit, it elevates higher. Now when the cue ball hits the object ball it could be going up (after a bounce?), going down, or (less likely on a fast hit) on a level plane. If the cue ball was going downward on contacting the object ball--- it may bounce backward.

cushioncrawler
02-18-2007, 10:30 PM
<blockquote><font class="small">Quote Qtec:</font><hr> There might be a bounce up. There could be a bounce forward. Bounce back- ball on ball? Don't think so.<hr /></blockquote> Q -- If the qball is "dead on line" with 2 balls that are frozen, and if u hit the qball to hit the first ball fullball, the qball will bounce back.

This sort of bounce-back can be a problem. For example, say that instead of hitting the 1stBall fullball u decide to hit it halfball -- u might expect the qball to follow the uzual halfball deflexion angle, but it wont, the qball will deflect (initially) at a much wider angle -- here, the qball will deflect at say 70dg instead of the old reliable 59dg (no, the halfball deflexion angle iznt ever initially 60dg, koz e is allways less than 1.00). Rezult, a scratch perhaps. This "wide deflexion angle" is a sort of bounce-back too. madMac.

colincolenso
02-20-2007, 06:29 AM
<blockquote><font class="small">Quote cushioncrawler:</font><hr> <blockquote><font class="small">Quote Qtec:</font><hr> There might be a bounce up. There could be a bounce forward. Bounce back- ball on ball? Don't think so.<hr /></blockquote> Q -- If the qball is "dead on line" with 2 balls that are frozen, and if u hit the qball to hit the first ball fullball, the qball will bounce back.

This sort of bounce-back can be a problem. For example, say that instead of hitting the 1stBall fullball u decide to hit it halfball -- u might expect the qball to follow the uzual halfball deflexion angle, but it wont, the qball will deflect (initially) at a much wider angle -- here, the qball will deflect at say 70dg instead of the old reliable 59dg (no, the halfball deflexion angle iznt ever initially 60dg, koz e is allways less than 1.00). Rezult, a scratch perhaps. This "wide deflexion angle" is a sort of bounce-back too. madMac. <hr /></blockquote>

Yes Mac,
That was probably a typical English 2-shot pool (blackball) set.

The CB is 1 15/16" (some are even 1 7/8" I believe) and OBs are 2". It is standard for the CB to bounce backward before rolling forward on firm straight shots.

It can come back nearly 6 inches on some power topspin shots. Needless to say, the prefered method for positional play in this game is stunning back.

Colin

Stretch
02-20-2007, 09:14 AM
<blockquote><font class="small">Quote colincolenso:</font><hr> <blockquote><font class="small">Quote cushioncrawler:</font><hr> <blockquote><font class="small">Quote Qtec:</font><hr> There might be a bounce up. There could be a bounce forward. Bounce back- ball on ball? Don't think so.<hr /></blockquote> Q -- If the qball is "dead on line" with 2 balls that are frozen, and if u hit the qball to hit the first ball fullball, the qball will bounce back.

This sort of bounce-back can be a problem. For example, say that instead of hitting the 1stBall fullball u decide to hit it halfball -- u might expect the qball to follow the uzual halfball deflexion angle, but it wont, the qball will deflect (initially) at a much wider angle -- here, the qball will deflect at say 70dg instead of the old reliable 59dg (no, the halfball deflexion angle iznt ever initially 60dg, koz e is allways less than 1.00). Rezult, a scratch perhaps. This "wide deflexion angle" is a sort of bounce-back too. madMac. <hr /></blockquote>

Yes Mac,
That was probably a typical English 2-shot pool (blackball) set.

The CB is 1 15/16" (some are even 1 7/8" I believe) and OBs are 2". It is standard for the CB to bounce backward before rolling forward on firm straight shots.

It can come back nearly 6 inches on some power topspin shots. Needless to say, the prefered method for positional play in this game is stunning back.

Colin <hr /></blockquote>

Hi Colin, you'd be a good one to ask this question too. I've been working on the Ronnie Alcano Break Shot. When i saw him Roll through the field in the World Championships i said Um-Hum maybe i ought to give this break a try. /ccboard/images/graemlins/smile.gif Anyway, what Ronnie had down was to break from the side rail and get a full ball hit, but he was able to draw the cue ball back to the side rail by his bridge hand, which would get the cue ball to the end rail and back up table a ways! The 1 ball just angled off the side rail and sat for an easy shot in the side pocket from where the cue ball finished.

So here's my question ( sorry about the long way round lol ) You'd think that the one ball supported by the whole rack would make it child's play to draw back the length of the table. With those bounce back effect combined with back spin you'd think that cb would literally take right off, it dosn't. This shot still takes the right blend of speed and spin to work. Plus you really need ideal conditions like super fast cloth and lively rails.

I'm wondering, does a bad contact take a lot of spin off the CB? On breakshots the speed forces the cb to become a little airborn if it does not meet the ob perfectly as they are both sitting then the curve of ball contacted will make it do funny things. Instead of that bounce back effect you speak of it almost looks like they are sticking a little bit or double kissing before the draw wins out. Is this just bad contact? or maybe a GAP in behind the head ball?

Anyway having tried to get this break shot to work for me i can only be amazed at how Alcano mastered it to kill everyone at the Worlds. St. &lt;sorry for the long post&gt;

dr_dave
02-20-2007, 03:10 PM
<blockquote><font class="small">Quote calcuttaman:</font><hr> Lets say you had a straight in shot, and you hit the cue ball just ever so slightly above center.

Would the cue ball "bounce back" somewhat then continue slightly forward?

Same situation but with definate top english. Is there any "bounce back" to the cue ball? <hr /></blockquote>
In case nobody has already pointed this out, another cause for the CB tending to "bounce forward" a little is the CB being slightly airborne. This is actually likely on follow shots, especially at higher speeds, because the CB gets "squirted" into the table and then jumps slightly (e.g., see HSV A.124 (http://www.engr.colostate.edu/~dga/pool/high_speed_videos/new/HSVA-124.htm)).

Regards,
Dave

Jal
02-20-2007, 07:01 PM
<blockquote><font class="small">Quote Stretch:</font><hr>...So here's my question ( sorry about the long way round lol ) You'd think that the one ball supported by the whole rack would make it child's play to draw back the length of the table. With those bounce back effect combined with back spin you'd think that cb would literally take right off, it dosn't. This shot still takes the right blend of speed and spin to work. Plus you really need ideal conditions like super fast cloth and lively rails.<hr /></blockquote>Stretch, Bob Jewett has pointed out that the effective mass of the rack for a straight on hit is not much more than that of a single ball! He used a figure of about 9/7'ths. If you slow down Dr. Dave's high speed video of an 8-ball break (http://www.engr.colostate.edu/~dga/pool/high_speed_videos/HSV7-6.htm), you can find that the cueball rebounds with a speed of 1/5'th to 1/6'th of its initial speed. This is consistent with an effective mass of about 9/7'th or 3/2's of a single ball.

As it happens, if you hit two balls squarely and simultaneously that are frozen to each other, ie, aiming at their mutual contact point, the conservation laws predict that the cueball will bounce back with 1/5'th of its speed. It seems then as if the rack acts like it consists of only the head ball and the two behind it, with separate, sequential collisions taking place (except for the simultaneous impact of the two behind the head ball).

The conservation laws also predict the rebound speed when the cueball is not hitting the two balls squarely, ie, not perpendicular to the line between centers. However, I haven't worked it out, and am not sure just how justified this 'reduced' model is in describing the cueball's reaction.

<blockquote><font class="small">Quote Stretch:</font><hr>I'm wondering, does a bad contact take a lot of spin off the CB? <hr /></blockquote>I doubt it, as a general rule, but can't say for sure at this point.

Jim

Stretch
02-20-2007, 08:18 PM
<blockquote><font class="small">Quote Jal:</font><hr> <blockquote><font class="small">Quote Stretch:</font><hr>...So here's my question ( sorry about the long way round lol ) You'd think that the one ball supported by the whole rack would make it child's play to draw back the length of the table. With those bounce back effect combined with back spin you'd think that cb would literally take right off, it dosn't. This shot still takes the right blend of speed and spin to work. Plus you really need ideal conditions like super fast cloth and lively rails.<hr /></blockquote>Stretch, Bob Jewett has pointed out that the effective mass of the rack for a straight on hit is not much more than that of a single ball! He used a figure of about 9/7'ths. If you slow down Dr. Dave's high speed video of an 8-ball break (http://www.engr.colostate.edu/~dga/pool/high_speed_videos/HSV7-6.htm), you can find that the cueball rebounds with a speed of 1/5'th to 1/6'th of its initial speed. This is consistent with an effective mass of about 9/7'th or 3/2's of a single ball.

As it happens, if you hit two balls squarely and simultaneously that are frozen to each other, ie, aiming at their mutual contact point, the conservation laws predict that the cueball will bounce back with 1/5'th of its speed. It seems then as if the rack acts like it consists of only the head ball and the two behind it, with separate, sequential collisions taking place (except for the simultaneous impact of the two behind the head ball).

The conservation laws also predict the rebound speed when the cueball is not hitting the two balls squarely, ie, not perpendicular to the line between centers. However, I haven't worked it out, and am not sure just how justified this 'reduced' model is in describing the cueball's reaction.

<blockquote><font class="small">Quote Stretch:</font><hr>I'm wondering, does a bad contact take a lot of spin off the CB? <hr /></blockquote>I doubt it, as a general rule, but can't say for sure at this point.

Jim <hr /></blockquote>

Thanks for the information Jim. By the sounds of it i could practice this break shot with just the top 3 balls and replicate a full rack fairly closely. It would sure save a lot of racking time! /ccboard/images/graemlins/smile.gif St.

Qtec
02-21-2007, 02:57 AM
My bad. I thought I was replying to the original post,ie one ball hitting another ball.
Q

colincolenso
02-21-2007, 08:27 AM
<blockquote><font class="small">Quote Stretch:</font><hr>
Hi Colin, you'd be a good one to ask this question too. I've been working on the Ronnie Alcano Break Shot. When i saw him Roll through the field in the World Championships i said Um-Hum maybe i ought to give this break a try. /ccboard/images/graemlins/smile.gif Anyway, what Ronnie had down was to break from the side rail and get a full ball hit, but he was able to draw the cue ball back to the side rail by his bridge hand, which would get the cue ball to the end rail and back up table a ways! The 1 ball just angled off the side rail and sat for an easy shot in the side pocket from where the cue ball finished.

So here's my question ( sorry about the long way round lol ) You'd think that the one ball supported by the whole rack would make it child's play to draw back the length of the table. With those bounce back effect combined with back spin you'd think that cb would literally take right off, it dosn't. This shot still takes the right blend of speed and spin to work. Plus you really need ideal conditions like super fast cloth and lively rails.

I'm wondering, does a bad contact take a lot of spin off the CB? On breakshots the speed forces the cb to become a little airborn if it does not meet the ob perfectly as they are both sitting then the curve of ball contacted will make it do funny things. Instead of that bounce back effect you speak of it almost looks like they are sticking a little bit or double kissing before the draw wins out. Is this just bad contact? or maybe a GAP in behind the head ball?

Anyway having tried to get this break shot to work for me i can only be amazed at how Alcano mastered it to kill everyone at the Worlds. St. &lt;sorry for the long post&gt; <hr /></blockquote>

Stretch,
Simply put, when you play the break as Ronnie did, it is very similar to playing the 1-ball as if it stands alone. It may come back a couple of foot further on occassion if the ball are touching in the right way, but it should be reasonably consistant.

Mind you, it's not that easy playing a consistant 7 foot draw shot with 5 foot separation to begin with. But with the mass of the pack, the variation will be more that playing a single ball, but not a huge variation imho.

Colin