Moving friction and Rolling friction about billiards HOT 5 CLOSED

I agree we could have separate coefficient of friction for sliding and rolling. The current code is based around:

https://billiards.colostate.edu/physics_articles/Han_paper.pdf

In that paper the rolling friction is related to the sliding friction by equation 8
That is in the code as:

export const Mxy = (7 / (5 * Math.sqrt(2))) * mu * m * g * 0.25

When I tried this without the 0.25 scaling factor the simulation did not feel realistic. I am open to having direct constant for Mxy if you know suitable values.

Diagrams are useful in choosing the values:

http://tailuge.github.io/billiards/dist/diagrams.html

Also from https://billiards.colostate.edu/physics_articles/Mathavan_IMechE_2010.pdf

"High-speed-camera-based measurements were used,
in a previous work by the present authors, to determine
the sliding coefficient of friction between a snooker
ball and the table-felt; the sliding coefficient of friction μs was found to be between 0.178 and 0.245 [16].
Marlow [12] suggests a value of 0.2 for the game of
pool. Since the present authors have performed extensive measurements of the various parameters related
to snooker [16], from here onwards the numerical values found in snooker are used for the calculations.μs is
assumed to be 0.212, as an average value"

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OK, thanks a lot!
I have already read the paper , and derived the formula about velocity and angle-velocity myself, but I just ignore the 0.25

Now I have an other question,

In physics.ts, line 9 - line 11

export function surfaceVelocityFull(v, w) {
return v.clone().add(upCross(w))
}

I think it should be

export function surfaceVelocityFull(v, w) {
return v.clone().add(upCross(w) * R) // Because R = 0.5 instead of 1.0
}

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I think you are correct since v=rw.

I cannot update the code directly now e.g.

export function surfaceVelocityFull(v, w) {
return v.clone().addScaledVector(upCross(w),R)
}

because I think this confusion of R=0.5 or R=1 occurs frequently throughout the code. I aim to fix this when I've found all places where this impacts.

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Take a look at

19614e6

I have made the equations match the paper directly with inclusion of R throughout.

The ball behaviour is about the same but I have now removed the odd 0.25 constant that was used earlier and mu is now 0.2 matching other papers values.

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Here is a break using some backspin. I think the spin is far too 'slippery' and the friction during sliding needs to be much higher whereas the rolling friction should stay low. Not sure how to achieve this without introducing a new factor into Mxy.

replay link

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