physics-based draw shot advice
- Thread starter dr_dave
- Start date
This is shown and described fairly clearly in the video (e.g., starting at the 1:38 point). Check it out. For almost all pool shots, the tip is in contact with the CB for only about 0.001 sec (one thousandth of a second)! For more info on tip contact time, see:nickgeo said:
Regards,
Dave
dr_dave said:
Dave,
You mean that different cue elevations, if hit the exact same point on the CB , doesnt influence tip offset??? This must be a mistake right?
recheck my az2.picture. I used your definition of tip offset, to draw the line of action and cb center, to compare the difference in tipoffset, and even though on both the cb is hit on the exact same point, the offset IS different.
Im using your own definitions here... I'm 100% sure of this. Ill eat my shorts if im wrong.
The drawings (even basic) don't lie right?
you stated= "the line of action of the cue and the center of the CB, regardless of the cue elevation "
This is a paradox. true 2 points there is only one line that can goe trough it. If the 2 points change, aka elevation, then the line changes... meaning that the offset also changes...
simple example: compare mass? shot vs 1tip of folow shot.
horizontal stroke + 1 tip of folow.
VS
vertical stroke + cue hits at the exact same spot as above (aka if looked horizontally, 1 tip above the center)
One will folow, the other will draw. So the tipofset HAS to be different. You can't neglect the angle of the line of action in the calculations. And the difference in results is only slightly influenced by the jump height, pusing into the slate, etc compared to the difference the different offset makes...
if i use your link ( i honestly dislike being refered to url's as an answer to a question, wich wasn't the goal of the study in the url)... Give me the formule you use to calculate tip offset, without using the angle of elevation or the alpha angle (same as 90? - elevation angle). If you can't, then the tip offset is NOT regardless of the cue elevation.
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using your own drawings: you post exactly the same as me, but you conclude the opposit.
if contact point would be same on both drawings, offset b would me smaller then offset x.
hope its clear now.
The only thing that cue elevation does that visibly helps, is increasing the amount of spin due to a bigger offset. But you can get the same offset with a horizontal cue if the contact point is lower, with same % chance of miscuing.
The only thing that is needed to powerdraw, is the right balance between speed and amount of spin, and as it has been shown, this is more complex then just MAX POWER, MAX OFFSET.
You should need to write a new article in the same line as
TP B.2 - Rolling resistance, spin resistance, and "ball turn"
but with contact resistance, spin resistance,
and aplaying your article about
http://billiards.colostate.edu/technical_proofs/new/TP_A-12.pdf
where you talk about linear impulse, wich automatically imply's, that the linear momentum is dependant on direction of the linear impulse aka the cue elevation,
and aply both things to the equation of powerdraw to incorporate them into the equation of wich speed gives the best powerdraw results.
You havent discussed the two points mentioned, but it explains why MAX speed itsnt correct for all shots :
Imagine you stroke the cb with draw with a strong stroke. The spin will "almost" be constant untill it hits the object ball. The friction this collision induces is in function of the speed at wich it hits the Object ball. (compare it to a spinning polisher, if you press your hand very heavily, it will spin slower, if you just lay down your fingers on it, it wont slow down).
So if you MAX power stroke with a draw shot the cb, the heavy contact between cb and OB will make the cb lose its spin alot more, then if the cb would hit the OB very softly. The collision induced friction of the OB wont slow the draw as much.
on the other hand tOO slow, and the roling induced friction of the cloth will reduced the draw more then the contact will.
You just need to judge witch friction will reduce the spinning cueball the most.
A The cloth friction or
B the collision induced friction.
use the speed that will give you the least losses, and maximise the offset to 80%
another i wanted to talk about that hasn't been used to do the math is this.
The more cue elevation you use, the higher the ball will jump, when it lands on the table (ideally at moment of impact with ob) the cb will bounce several times more then of the ball highest place would be lower with a lower cue elevation.
The cb can only draw back once it has "permanent" contact with the cloth. Without cloth it can't draw. so the longer it rebounds at the place of impact with the ob, the more time draw you will lose. Its is very visible in this video of yours dave :
http://billiards.colostate.edu/high_speed_videos/new/HSVB-24.htm . Watch the cb , its takes 0.5seconds after impact before it starts drawing back. That ALOT of time. That why i advocate a very slight cue elevation, just enough so that at the ideal speed for max draw, the cb bounces all the way to the OB without going to high in the air, and rebounding to often.
edit: with a closed bridge and max tipofset, the angle and rebound are to hight, for the cb the get permanent contact with the cloth to be able to draw back after impact. I can draw the cb 30% further with a flat bridge then with a closed bridge, with same offset and same speed. I use a closed bridge 98% of the time. 2% are for powerdraws.
if contact point would be same on both drawings, offset b would me smaller then offset x.
hope its clear now.
The only thing that cue elevation does that visibly helps, is increasing the amount of spin due to a bigger offset. But you can get the same offset with a horizontal cue if the contact point is lower, with same % chance of miscuing.
The only thing that is needed to powerdraw, is the right balance between speed and amount of spin, and as it has been shown, this is more complex then just MAX POWER, MAX OFFSET.
You should need to write a new article in the same line as
TP B.2 - Rolling resistance, spin resistance, and "ball turn"
but with contact resistance, spin resistance,
and aplaying your article about
http://billiards.colostate.edu/technical_proofs/new/TP_A-12.pdf
where you talk about linear impulse, wich automatically imply's, that the linear momentum is dependant on direction of the linear impulse aka the cue elevation,
and aply both things to the equation of powerdraw to incorporate them into the equation of wich speed gives the best powerdraw results.
You havent discussed the two points mentioned, but it explains why MAX speed itsnt correct for all shots :
Imagine you stroke the cb with draw with a strong stroke. The spin will "almost" be constant untill it hits the object ball. The friction this collision induces is in function of the speed at wich it hits the Object ball. (compare it to a spinning polisher, if you press your hand very heavily, it will spin slower, if you just lay down your fingers on it, it wont slow down).
So if you MAX power stroke with a draw shot the cb, the heavy contact between cb and OB will make the cb lose its spin alot more, then if the cb would hit the OB very softly. The collision induced friction of the OB wont slow the draw as much.
on the other hand tOO slow, and the roling induced friction of the cloth will reduced the draw more then the contact will.
You just need to judge witch friction will reduce the spinning cueball the most.
A The cloth friction or
B the collision induced friction.
use the speed that will give you the least losses, and maximise the offset to 80%
another i wanted to talk about that hasn't been used to do the math is this.
The more cue elevation you use, the higher the ball will jump, when it lands on the table (ideally at moment of impact with ob) the cb will bounce several times more then of the ball highest place would be lower with a lower cue elevation.
The cb can only draw back once it has "permanent" contact with the cloth. Without cloth it can't draw. so the longer it rebounds at the place of impact with the ob, the more time draw you will lose. Its is very visible in this video of yours dave :
http://billiards.colostate.edu/high_speed_videos/new/HSVB-24.htm . Watch the cb , its takes 0.5seconds after impact before it starts drawing back. That ALOT of time. That why i advocate a very slight cue elevation, just enough so that at the ideal speed for max draw, the cb bounces all the way to the OB without going to high in the air, and rebounding to often.
edit: with a closed bridge and max tipofset, the angle and rebound are to hight, for the cb the get permanent contact with the cloth to be able to draw back after impact. I can draw the cb 30% further with a flat bridge then with a closed bridge, with same offset and same speed. I use a closed bridge 98% of the time. 2% are for powerdraws.
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I'm sure you know this, but it also changes the ratio of spin to forward speed. For instance, if you elevate the cue to perpendicular, forward speed will be minimal (like an extreme masse).
pj
chgo
This is an incomplete quote. Dave actually said "'tip offset' is always measured between the line of action of the cue and the center of the CB, regardless of the cue elevation"
In other words, I think he's saying the same thing you are.
pj
chgo
Solartje
Sorry, I dont agree with your max draw is affected by higher friction because you hit the ball harder. If hitting the ball harder causes higher friction thin collision induced throw would also be greater with a harder stroke. We know that it isnt.
I'm guessing that max draw doesent occur at 100% on a hard stroke is like throwing a feather vs throwing a base ball. The base ball has more mass to absorb the power. At 100% draw the cue is glancing of and not able to put max energy into the CB.
Sorry, I dont agree with your max draw is affected by higher friction because you hit the ball harder. If hitting the ball harder causes higher friction thin collision induced throw would also be greater with a harder stroke. We know that it isnt.
I'm guessing that max draw doesent occur at 100% on a hard stroke is like throwing a feather vs throwing a base ball. The base ball has more mass to absorb the power. At 100% draw the cue is glancing of and not able to put max energy into the CB.
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Patrick Johnson said:
exactly, thats what my graphic #1 stated. with speed i mean forward speed.
sorry my english and terms might not always be perfect.
bigger offset means less forward speed.
Patrick Johnson said:
now that i re-read you are correct. the measuring method is the same. I thought he stated the result (the offset) was the same. I wanted to clearly add this, as most people dont know that hitting the same contact point gives different tip offsets if elevated. Why do i get more draw when elevating the cue???? because you are hitting the CB "lower" , eventhough you are
not touching the cb in a lower place. i know alot of people have a hard time understanding this and the math pdf's might not always be clear to everyone , for this to be clear to them.
jtompilot:
I checked out the high speed video's and see if collision friction would decrease the amount of draw. (in his 9ball break with draw) and it does seem to be almost neglectible. It MUST have some influence, but its not visible on the video. I can understand that dave didn't take this in account on the math side, to make it more easy. I still think there alot of other things that he didnt take into account, for it to be usefull. for example the amount of rebounds after contact... if it takes 0.5sec before the cb has contact with the cloth, thats alot of drawdistance lost.
In his math he used a perfect horizontal stroke, so there is no rebound etc, but if he does part II about cue elevation, this should be adressed, and maybe dave already thought about this. Just wanted to add some notes that i would like to see added.
im in NO way saying dave's work is a bad thing.
just i'm still missing some things, that might or might not be off insignifant importance in the results and looking forward for the partII. I just understood his post wrongly, and wanted to make it clear that tip offset isn't the same as just the distance between horizontal center hit and contact points. (wich many friends seemed to have thought)I thought collision friction would have an influence, and the collision friction would be higher with higher forward speeds. doesnt speed influence collision induced throw? i thought it did, might be wrong, never really got into depth into this one.
But i do think that i am right when i say the forward speed influences the collision friction of OB-CB. cloth Friction is influenced by cloth surface...(dont know the word in english, roughness?), gravity and mass of the object in a vertical plane. cb hitting OB , is the same rotated 90%. where gravity is replaced with forward speed. cloth roughness replaced with OB roughness, and mass stays the same. am i wrong on this one?
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I'd never really thought about the translational losses v increased spin:speed ratio though it makes perfect sense.
I think this info will save me a few miscues. Something I've done far too often attempting power draws.
I still think there's a good argument for applying near miscue low hits for what I call nip draw shot. i.e. When trying to hold the tightest possible angle on an angled draw shots. Perhaps Jal has some insights here.
Colin
I think this info will save me a few miscues. Something I've done far too often attempting power draws.
I still think there's a good argument for applying near miscue low hits for what I call nip draw shot. i.e. When trying to hold the tightest possible angle on an angled draw shots. Perhaps Jal has some insights here.
Colin
The point of my post and illustrations was: the "tip offset" is defined as the perpendicular distance between the line of the cue (through the contact point) and the center of the CB. To create the same tip offset, the required contact point on the CB surface will be different for each cue elevation. I think the focus should be on "tip offset" (which can be the same at different cue elevations), not the contact point on the CB (which, for a given "tip offset," changes with cue elevation and tip shape).Solartje said:
Sorry for the confusion,
Dave
Dont be sorry dave, the error was all mine . I misread your post.
another question : if i understand the graphics correct, does this mean different speed influence the miscue limit?
On the drawdistance VS speed graphic for different b offsets (dont remember the exact graphic letter),
the line for a high offset ends sooner then with low offset. is this because the graphic limits where limited, or because for a higher offset, the maximum speed that can be used is lower because the higher the speed, the less further the miscue limit is?
aka
if you stroke slower, does this increases the miscue limit, so you can use a higher offset?
how about the amount of collision friction for different contact angles? are they worth taking them into the equation?
PS i think part II where you take into account elevation, will be a pain in the *** you are correct. there is SO much involved.
another question : if i understand the graphics correct, does this mean different speed influence the miscue limit?
On the drawdistance VS speed graphic for different b offsets (dont remember the exact graphic letter),
the line for a high offset ends sooner then with low offset. is this because the graphic limits where limited, or because for a higher offset, the maximum speed that can be used is lower because the higher the speed, the less further the miscue limit is?
aka
if you stroke slower, does this increases the miscue limit, so you can use a higher offset?
how about the amount of collision friction for different contact angles? are they worth taking them into the equation?
PS i think part II where you take into account elevation, will be a pain in the ***
you are correct. there is SO much involved.
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Colin,Colin Colenso said:
That's a good point. There are some cases where maximum spin-to-speed ratio is more important than maximum spin. Mike Page listed several examples in post 64. When I get some time, I will add spin-to-speed ratio graphs and conclusions to the analysis.
Regards,
Dave
PS: Where have you been lately?
No problem.Solartje said:
I'm not sure what "graphics" you are referring to. I have not studied the effect of speed on the miscue limit. The miscue limit could be affected by tip thickness and hardness and by cue speed, but I think any such variations would be too small to have any practical value. But again, I have not studied this, and I probably won't unless I get a much better high-speed camera ... mine is inadequate for the job.Solartje said:
I think you are referring to Graph K. This graph has nothing to do with miscue limit. It shows how the more you increase speed, the more draw distance you get. This applies to all tip offsets. The curves are chopped off due to the limited scale of the graph, but they keep rising.Solartje said:
Regards,
Dave
Thanks for alerting me to Mike Page's post. That's exactly what I was thinking about and certainly an aspect of draw players need to be aware of. That said, your measurements and insight into less that max offset hitting is a great tip.dr_dave said:
Been away for a few weeks since the DCC. The passing of a close pool mate and some subsequent activities and fundraisers have kept me pretty busy.
Colin
dr_dave said:
Yes that was the graph i was refering too. i hear you loud and clear
Can't wait for the speed/spin ratio graphics. those will be very interesting like mike stated.
What is your opinion on using a low open bridge vs a higher closed bridge for same tip offset, on the draw distance. Am i right to asume that the low bridge, makes for a smaller jumpangle for same offset as a closed bridge, wich in his turn give less rebounds, and so gives more drawdistance?
First THANKS for all info. you have posted and will post in the future!!!
I have found for long drawshots-5ft or more between cb and ob-if I get
real low to table and strike cb low as possible as hard as I can "smoothly",
I obtain maximum draw.Now that seems basic,but my question is this;Is it possible that I'm actually striking cb low enough to lift it from the cloth so
friction is reduced thus allowing more draw?I know that "bounce" causes
loss of cb control but slight lifting,if it were to occur,would induce less
bounce then downward driven draw. Thanks again.
I have found for long drawshots-5ft or more between cb and ob-if I get
real low to table and strike cb low as possible as hard as I can "smoothly",
I obtain maximum draw.Now that seems basic,but my question is this;Is it possible that I'm actually striking cb low enough to lift it from the cloth so
friction is reduced thus allowing more draw?I know that "bounce" causes
loss of cb control but slight lifting,if it were to occur,would induce less
bounce then downward driven draw. Thanks again.
Sir--Spent a bunch of hard time on the video that you referred me to. Reminded me of that physics course that I couldn't handle years ago, but almost fun because it was pool. It was not simple to understand speed versus distance rather than time. And time went backwards in the video. Like the trick questions on those cruel tests!
Anyhow, permit me a couple of comments/observations/questions. In all of this I worked out that the points on the graphs are time markers equally spaced in time. There are 40 or 41 points and the total time is 1220 frames times 1/3000 (3000 frames per second). And the whizzing clock seemed to show around .4 seconds duration, even if backwards. So these time markers are about .01 seconds apart. I hope I got this much right.
On Mr. Jewett's graph:
1. There are 3 or 4 points just before the big drop that are very close in the distance direction. That suggests to me that the cue is moving more slowly that at the previous several points, that are farther apart. Yet the speed given on the speed axis is the same for all of these points. I don't understand how this can be. This is even more noticeable on the Dr.'s graph. Am I misunderstanding this?
2. The voice-over and vertical red rectangle indicate the points that represent the contact time and that speed decreases during that time. From the red rectangle and from the points where speed decreses, it's about 6 or 7 points, or .06 seconds. That's a lot more time that the one-thousandth of a second that you mentioned in an earlier e-mail. Or did I blow the math here or earlier on.
3. How do we know that the cue is no longer in contact with the cueball after the cue speeds up again? Perhaps the contact has slowed down the cue, speeded up the cue ball, and now they are moving as one (like my original question about putting the tip against the cue ball, stroking and getting draw).
4. If instead the cue ball and the cue separate at the bottom of the vertical red rectangle as per the voiceover information, why doesn't the cue then hit the cue ball again? At the very moment of separation I would think that the cue ball is going a teeny tiny bit faster than the cue. But then the cue speeds up according to the graph and the cue ball should begin to slow down due to the cloth. The cue would win the race.
5. Is my assertion that the key speed is that at separation rather than at initial contact correct?
6. Going back to the drawing board, I would love to see an experiment with Mr. Jewett's lovely pendulum stroke where he hits the draw shot on the early part of his stroke (accelerating) and then does it again on the decelerating ending part of his stroke, both at the same speed. My bet is on the early Mr. Jewett to get the big draw.
Thanks,
Nick
Anyhow, permit me a couple of comments/observations/questions. In all of this I worked out that the points on the graphs are time markers equally spaced in time. There are 40 or 41 points and the total time is 1220 frames times 1/3000 (3000 frames per second). And the whizzing clock seemed to show around .4 seconds duration, even if backwards. So these time markers are about .01 seconds apart. I hope I got this much right.
On Mr. Jewett's graph:
1. There are 3 or 4 points just before the big drop that are very close in the distance direction. That suggests to me that the cue is moving more slowly that at the previous several points, that are farther apart. Yet the speed given on the speed axis is the same for all of these points. I don't understand how this can be. This is even more noticeable on the Dr.'s graph. Am I misunderstanding this?
2. The voice-over and vertical red rectangle indicate the points that represent the contact time and that speed decreases during that time. From the red rectangle and from the points where speed decreses, it's about 6 or 7 points, or .06 seconds. That's a lot more time that the one-thousandth of a second that you mentioned in an earlier e-mail. Or did I blow the math here or earlier on.
3. How do we know that the cue is no longer in contact with the cueball after the cue speeds up again? Perhaps the contact has slowed down the cue, speeded up the cue ball, and now they are moving as one (like my original question about putting the tip against the cue ball, stroking and getting draw).
4. If instead the cue ball and the cue separate at the bottom of the vertical red rectangle as per the voiceover information, why doesn't the cue then hit the cue ball again? At the very moment of separation I would think that the cue ball is going a teeny tiny bit faster than the cue. But then the cue speeds up according to the graph and the cue ball should begin to slow down due to the cloth. The cue would win the race.
5. Is my assertion that the key speed is that at separation rather than at initial contact correct?
6. Going back to the drawing board, I would love to see an experiment with Mr. Jewett's lovely pendulum stroke where he hits the draw shot on the early part of his stroke (accelerating) and then does it again on the decelerating ending part of his stroke, both at the same speed. My bet is on the early Mr. Jewett to get the big draw.
Thanks,
Nick
Some people think a little elevation can actually help; but for me the jury is still out. The lift you describe would be possible only if the squirt angle your shaft produces is larger than the elevation angle of your cue. This probably isn't likely.alphadog said:
Regards,
Dave