Throw

[Bob Jewett]

... I imagine cleanliness of the balls is also a factor.

It's not just cleanliness. I had a pretty beat up set of Aramiths one time. I used car rubbing compound and then car polish. They looked beautiful, but the throw was maybe twice the normal amount. You could make remarkable maximum throw shots and banks, but normal shots behaved unexpectedly. I imagine that the chemicals in the car stuff left the balls' surfaces sticky.

 

[Robert Raiford]

Here's a plot of measurements I did in about 1984.

So the answer is that for some cut angles, the throw angle is the same for all speeds while for thinner cut angles, the throw angle decreases with more force.

Bob didn't mention it explicitly in his post, but I believe his chart shows throw curves for stun shots specifically (i.e. minimal follow or draw at impact). Shots with significant follow or draw don't have maximum throw around a half-ball hit (the peak in the curves around 30 degrees) but instead have throw that increases steadily with cut angle.

Robert

 

[Bob Jewett]

Bob didn't mention it explicitly in his post, but I believe his chart shows throw curves for stun shots specifically (i.e. minimal follow or draw at impact). Shots with significant follow or draw don't have maximum throw around a half-ball hit (the peak in the curves around 30 degrees) but instead have throw that increases steadily with cut angle.

Robert

Another thing to note is that the collision-induced throw with draw or follow will always be less than for the same angle and speed with stun. This hasn't been widely known until the last ten years or so.

 

[book collector]

What aiming system are you using ?

 

[ridinda9]

but the laws of physics are only guidelines ! Flexible ones !

mods, cmon....delete this poll/thread.

you cant create a poll where there question is governed by the laws of physics.

Bumblebees continue to fly , in spite of all the scientists who state that the displacement of air by their wings is incapable of supporting their weight !

there are exceptions to every rule !

 

[Bob Callahan]

Another thing to note is that the collision-induced throw with draw or follow will always be less than for the same angle and speed with stun. This hasn't been widely known until the last ten years or so.

Friction in ball-to-ball impacts is very complicated. One of the things I realized just before I quit thinking about the physics of pool 18 years ago, was that friction in the contact area is probably in the form of annular rings of stick and no-stick.

Seesh!...Next we'll be talking about inverse stiffness tensors and eigenfrequencies for LD shafts!

 

[Charlie Edwards]

Another thing to note is that the collision-induced throw with draw or follow will always be less than for the same angle and speed with stun. This hasn't been widely known until the last ten years or so.

I remember when you first stated these facts on RSB. Thanks for doing so. This is the single most important information about aiming without english ever revealed, IMO.

 

[Robert Raiford]

Another thing to note is that the collision-induced throw with draw or follow will always be less than for the same angle and speed with stun.

Right. I tend to think of follow/draw shots as becoming increasingly more stun-like as cut angle increases since there's progressively less of a contact point velocity contribution from the follow to keep the throw vector oriented as vertically.

This hasn't been widely known until the last ten years or so.

I'm guessing you stuck "widely" in there because Coriolis described the effect of follow and draw on throw almost 200 years ago with his collision model. He did assume speed-independent friction, though, so his model didn't capture the speed dependence shown in your diagram. However, the throw-reducing effect of follow/draw was there (along with sidespin and inelasticity effects).

If only Coriolis had played more pool, then maybe we wouldn't have had to wait so long to appreciate its full significance. Many thanks to you and others for bringing it to wider attention and enriching our understanding of throw in general!

Robert

 

[dr_dave]

Right. I tend to think of follow/draw shots as becoming increasingly more stun-like as cut angle increases since there's progressively less of a contact point velocity contribution from the follow to keep the throw vector oriented as vertically.

Good description; although by "as vertically" did you mean "more horizontally?"

FYI, I have a good theoretical plot and some experimental data on this topic in my October '06 BD article. Check it out.

I'm guessing you stuck "widely" in there because Coriolis described the effect of follow and draw on throw almost 200 years ago with his collision model. He did assume speed-independent friction, though, so his model didn't capture the speed dependence shown in your diagram. However, the throw-reducing effect of follow/draw was there (along with sidespin and inelasticity effects).

If only Coriolis had played more pool, then maybe we wouldn't have had to wait so long to appreciate its full significance. Many thanks to you and others for bringing it to wider attention and enriching our understanding of throw in general!

I was shocked (and humbled) when I first read the English translation of Coriolis' tome on billiards physics. I only wish his book had been available in English sooner. Coriolis is certainly my hero, as is Bob (2nd only to Coriolis on my billiards-physics hero list).

Regards,
Dave

 

[Bob Callahan]

I was shocked (and humbled) when I first read the English translation of Coriolis' tome on billiards physics. I only wish his book had been available in English sooner. Coriolis is certainly my hero, as is Bob (2nd only to Coriolis on my billiards-physics hero list).

Regards,
Dave

I cheated a little on this. George Onoda had it translated by a student who knew archaic French, and sent me a copy about 20 years ago.
Prior to that, I could only get a microfilm copy from Cornell, and struggle through it with my very, very weak French.

Bob and you have each contributed enormously to the science of billiards. Thank you.

 

[GetMeThere]

Bumblebees continue to fly , in spite of all the scientists who state that the displacement of air by their wings is incapable of supporting their weight !

there are exceptions to every rule !

No "scientist" (or aerodynamics engineer) states that. The idea apparently arises from a question asked at a dinner between a biologist and an aerodynamics STUDENT. The answer given was wrong, based then on an incomplete understanding of biologic flight vs mechanically designed flight. The part played by "lift" in the flight of winged animals is now a phenomenon that's quite well understood.

Here's one of many sites that give an brief explanation and debunking to the "science says bumblebees can't fly" myth.

 

[Robert Raiford]

Right. I tend to think of follow/draw shots as becoming increasingly more stun-like as cut angle increases since there's progressively less of a contact point velocity contribution from the follow to keep the throw vector oriented as vertically.

Good description; although by "as vertically" did you mean "more horizontally?"

No, I definitely meant "as vertically" in the context of that admittedly awkward sentence. Perhaps it makes it easier to parse by adding "as for smaller cuts" to the end. But you're right, I could have also stated that the progressively-reduced follow contribution causes the throw vector to be oriented more horizontally with increasing cut angle. Geez, that's what editors are for, isn't it?

[Warning: dubious rationalization ahead!]

Anyway, I'm sure the reason I wrote it like that is because my - ahem - natural optimism led me to think of it in terms of the positive idea of using the presence of follow to keep it as vertical as possible rather than the negative idea of the absence of follow causing it to be more horizontal. Half full or half empty? Physics remains indifferent.

I was shocked (and humbled) when I first read the English translation of Coriolis' tome on billiards physics. I only wish his book had been available in English sooner. Coriolis is certainly my hero, as is Bob (2nd only to Coriolis on my billiards-physics hero list).

Me too on all points, although my shock came with the French version. I suffered through learning to read French specifically to digest Coriolis before I knew anything about the translation. It was a painfully slow process - made slower by printing errors - but fortunately I had a girlfriend at the time who was fluent and willing to make the process more...interesting

Robert

 

[rebound]

The lesser the extent of throw (at any one given contact point). This is according to Dr. Dave's FAQs page.

I have issues with the demonstrations in that video but I've been such an argumentative dick lately I'm going to stay mum other than to say I abstain.