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Comment by tsimionescu | Hacker News Reader

This is a complete tangent, but I would note that we don't have physical models nearly good enough to actually compute the way billiards balls (or even worse, snooker balls) interact with each other and the fabric on the table. It's all guesswork and experience, mostly. The interactions between the balls and the fabric are critical for the vast majority of the movements, and they are far too complex for any physical first-principles based model to capture.

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If anyone is seeking serious answers about the variables, the first bible is "Byrne's New Standard Book Of Pool And Billiards."

And it's not just the cloth and balls (rolling and static friction, dirt, ball elasticity...), it's also the rails, which rarely exhibit "angle of reflection == angle of incidence" due to more complexities.

Humidity also plays a huge factor with the felt, same with the tip of your cue and how it hits.

If a tournament is using Andy Cloth (Taiwan based producer), I won't even bother entering.

Their felt isn't a consistent thickness, and if you put heavy English on the cue ball, there's a chance that it will suddenly grip and change direction in the middle of the table if you're not powering the shot in.

Simonis it is, then?

Simonis is pretty much the gold standard. Their 860 is my preference, but their others play really well too.

The Predator Arcadia is good, but plays really fast.

Haven't really had issues with the other brands I've played on (aside from Andy), although humidity really affects the Valley Ultra cloth.

Had a tournament on Valleys when a rain storm came through a few hours into it. Without hearing the rain or looking outside, I could tell it was raining. The tables slowed down dramatically.

Edit: Slight side note, avoid tables by doors to the outside. The fluctuations in temperature really messes with how true the table plays.

Is this because of imperfections in the fabric? Golf has a similar situation where if you use a machine to roll a ball on a perfect line and speed, sometimes it won’t go in. This is because of imperfections in the gradient and that grass changes constantly as it slowly grows and bends towards light, etc.

Wow now that’s a tangent to a tangent!

There was still ongoing dispute between pool and snooker players whether playing side spin on white ball affects angle of the object ball hit by the white (ignoring deflection, just the spin transfer).

In real life it depends on the tables bed, banks, cloth (different material, speed, whether it's clean or dirty, it's 'mileage', air temperature and humidity...), balls, cue and of course human factor.

seems like you could test this. simply line up a very easy (and repeatable) combination shot with the two object balls really close to each other and vary the contact and spin as needed. the closer the cue ball to the first object ball will mean that you could minimise the impact of deflection. have to try it next time I'm near a pool table!

I've always assumed that deflection, swerve and throw were a given but sounds like they're debating the "throw" part?

Not imperfections, the fabric itself. If the balls were on a frictionless surface, their movement would be completely different, they would barely spin. Much of their movement is caused by their interaction with the fabric. But that is very hard to model from Newton's laws of motion.

Why are snooker balls harder to model?

Not the balls themselves, but I believe the fabric is thicker, and thus has a bigger effect on the balls' motion, on snooker tables compared to pool. There are also other difficulties, such as the cue having a smaller tip that brings more variability in the spin imparted to a ball, but those I think are less relevant to the ability to model the game from first principles (Newton's laws of motion).

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