How fast does it spin?

[SpiderWebComm]

Posting in a thread you don't care about just to say you're not interested is about as lame as it gets.

pj
chgo

However, it's perfectly normal to post in thousands of threads with over 200,000 posts in various pool forums regarding one particular subject over a 19 year period when there's only somewhat of a slight interest but no interest in personal usage. :shakehead:

 

[Jal]

I'm also interested is how much sidespin wears off as the ball rolls on the table surface. ..

Dr. Dave's technical proof TP B.2 (see page 4) uses a figure of 10 rad/sec/sec. This is a static spin-down rate (ball not otherwise moving) which he gleaned from videos. He uses this figure in his analysis of a ball moving across the cloth as well.

So if the ball has an initial sidespin rate of Wi (in radians per second), after t seconds its sidespin rate will be:

W = Wi - 10t

TP B.2, along with many, many other gems, is located here:

http://billiards.colostate.edu/technical_proofs/index.html

Jim

 

[Jal]

However, it's perfectly normal to post in thousands of threads with over 200,000 posts in various pool forums regarding one particular subject over a 19 year period when there's only somewhat of a slight interest but no interest in personal usage. :shakehead:

Yes it is. :grin:

Jim .... except it's been bordering more on the heroic.

 

[Bob Jewett]

Interesting. So, it's kind of like a drill bit, where a larger diameter bit meets a lot more resistance at the interface with the material it's boring into?

Yes, I think it's related to the "lever arm" of the patch at the bottom of the ball. It looks moderately complicated to model in the case of a ball on cloth since the pressure is greatest at the center of the patch but the lever arm and the circumference both increase as you look at points away from the center.

Friction is much more involved than they taught in my high school.

 

[SpiderWebComm]

Yes it is. :grin:

Jim .... except it's been bordering more on the heroic.

And your group claims CTEer's are brainwashed? LMAO. Heroic? Somebody is brainwashed alright but it isn't those using CTE.

If Pat Johnson gunned down a CTE advocate you'd be first in line to say it was justifiable homicide or pleading the insanity card for his innocence.

Maybe it would be best to plead insanity right now for both of you because it's bordering on that and you should forget any future postings and his heroism.

 

[Sloppy Pockets]

Yes, I think it's related to the "lever arm" of the patch at the bottom of the ball. It looks moderately complicated to model in the case of a ball on cloth since the pressure is greatest at the center of the patch but the lever arm and the circumference both increase as you look at points away from the center.

Cloth seems to be a big factor, but doesn't the mass of the ball make a big difference as well? Your experience with spin dying in snooker must have a lot to do with the lighter balls, don't you think? When I watch English 8-ball, the small balls just seem to die, especially the little, tiny CB.

I guess the best of all worlds for spin would be a massive ball and thin, slick cloth like in 3-cushion.

Friction is much more involved than they taught in my high school.

Yeah, even in college we didn't spend too much time exploring friction. The way I see it, half the game comes down to the effects of friction in one way or another.

 

[Sloppy Pockets]

Dr. Dave's technical proof TP B.2 (see page 4) uses a figure of 10 rad/sec/sec. This is a static spin-down rate (ball not otherwise moving) which he gleaned from videos. He uses this figure in his analysis of a ball moving across the cloth as well.

So if the ball has an initial sidespin rate of Wi (in radians per second), after t seconds its sidespin rate will be:

W = Wi - 10t

TP B.2, along with many, many other gems, is located here:

http://billiards.colostate.edu/technical_proofs/index.html

Jim

Thanks, Jim. I'll try to work though Dave's proof when my brain feels a little fresher (and the DCC matches are over for the day).

 

[Jal]

If Pat Johnson gunned down a CTE advocate you'd be first in line to say it was justifiable homicide or pleading the insanity card for his innocence.

In a recent thread I actually did disagree with him. It took a exceedingly painful catharsis to overcome my obligate sycophantic urges, but it did happen! In your example, I would have to draw the line there too, somehow...unless of course the advocate was attempting to "prove" CTE by demonstrating it to him in person.

Maybe it would be best to plead insanity right now for both of you because it's bordering on that and you should forget any future postings and his heroism.

I'm actually a bit worried about your mental health. It seems to me that, anymore, most of your posts contain or consist entirely of personal attacks on him. If CTE were all it's claimed to be, it would thrive on its own merits, Patrick be damned (oops, can I say that?). In fact, according to some of you, it already is. So why this obsession with him? Why not 1) slough him off, and 2) see things from the perspective that we're just talking about pool for heaven's sake. However passionate you may be about it, it is, in the end, just a game.

Maybe I'm misreading you and you aren't as angry as you sometimes seem. I sincerely hope so.

Jim

 

[dr_dave]

For those interested and want more info or demonstrations, I've provide resource links below dealing with each of Bob's statements.

You can easily hit the cue ball with enough follow that it is rolling smoothly on the cloth from the start.
...
If you go very close to a miscue, you can get slightly more spin than that.

natural roll, maximum offset, and overspin

If you know how fast the ball is moving, then it's easy to calculate the RPMs.
...
Break speeds go to 30MPH or so, but that's hitting the ball in the center, more or less. Figure about 15MPH with full follow.

TP A.12 - The relationship between cue ball spin and cue tip offset
TP A.30 - The effects of cue tip offset, cue weight, and cue speed on cue ball speed and spin

As mentioned on Dr. Dave's site and as has been discussed here before, if you want to increase the side spin to speed ratio, you can mix in some draw with the side spin. That slows the cue ball on the way to the target but the side spin remains. Depending on how far off-center you feel you can hit, for maximum effect you want to hit at 4:00 or 8:00.

drag shot sidespin intensification

Enjoy,
Dave

 

[Corwyn_8]

Cloth seems to be a big factor, but doesn't the mass of the ball make a big difference as well? Your experience with spin dying in snooker must have a lot to do with the lighter balls, don't you think? When I watch English 8-ball, the small balls just seem to die, especially the little, tiny CB.

I guess the best of all worlds for spin would be a massive ball and thin, slick cloth like in 3-cushion.

Yeah, even in college we didn't spend too much time exploring friction. The way I see it, half the game comes down to the effects of friction in one way or another.

I tried playing pool on one of those 'friction-less surfaces' I got from the Physics 101 warehouse. It sucked bad. And man, was it a pain to install...


The mass of the ball doesn't matter as far as spin/speed go (both are proportional to mass so it cancels out). Taking the simplest case (normal roll). Normal roll is achieved on ANY ball by hitting it 2/5 of the way from equator to top. The 2/5 comes from the equation for moment of inertia of a sphere I=2/5mr². Normal roll gives spin / speed ratio of 1 revolution / 2π * (radius). The same can be said for side spin shot at 2/5 distance from vertical center (only the spin won't decay as fast). Moving further from the center creates a greater spin/speed ratio. So absent heroic measures (namely another force), spin/speed ratio is solely dependent on distance struck from center ball (as measure from the line of force of the cue).

You might want to think about spin/speed in units of 'natural roll'.

Thank you kindly.

 

[SloMoHolic]

Hello friends,

It's been a while since I've been active on AZB, but thought I'd chime in for this one, just for fun.

From a visual observation of various slomo videos, the fastest instantaneous rotation I've seen on a cue ball (limited to my own shots) is around 1400 - 1700 RPM, about twice as fast as your idling car engine.

This is not a definitive statement at all - just an observation taken by visually judging the rate of rotation of a cue ball in a slomo video, then multiplying that by the "slow motion factor" of that particular slomo video. It's absolutely possible that other players can achieve higher (or lower) RPM.

To see some examples for yourself, you can look at my old videos and count the rotations to get a rough idea of the RPM as shown in the video (but do it quickly because it slows down surprisingly fast). If you have a musical background, you will get a feel for the "beats per minute" or speed of the cue ball rotation. Then simply multiply that by 8 or 14 or or whatever the factor is for the particular slomo clip you're watching.

All shots from 0:50 to 1:20 in the video link below were shot at 420 frames per second, and are now played back at 30 frames per second. That is a factor of 14. Conveniently, the main downbeats in the music are at 60 beats per minute (or 1 per second, duh!).

(Keep in mind that the rest of this video uses a combination of other speeds as well, so the "slomo factors" range from 4 to 33.)

So, if the cueball is completing one full revolution per musical downbeat, that would be 60 RPM x 14 = 840 RPM. In several of the shots, the cueball appears to approach two revolutions per musical downbeat, or about 1680 RPM. These aren't cold hard facts, just a quick visual/mental observation with a little math to convert units.

Use the music and the dots on the measle ball to help you judge the rotational speed. As you watch, your interpretation of the rotation may be a little different than mine.

Again, I didn't post this to settle any arguments. I just thought it'd be cool to be able to put an approximate number on some actual RPMs. Maybe it will come in handy as a reality check for whatever the math/physics equations come up with. Good luck with your research!

Here's the link. Judge for yourself. Have fun!
http://www.youtube.com/watch?v=dN5_NrkjQj8

-Blake