Coefficient of Friction

[Donner]

Hey,

I've a question: Probably most of you, know what the Coefficient of Friction is.

Well, currently I am working on a racegame and now I want to implement physics - but there should be different materials, on the one side different materials for the tires and different street materials.

I don't want to define the coefficient of friction for the friction between all materials, but I thought it should be possible to have one value for the street and one for the tire and then to calculate the coefficient of friction from the two values.

Is there such a unit in physics, which describes the roughness of one material?
If not, what do you suggest to do?

Thanks a lot
D.

[JP]

The friction is the roughness isn't it?

Are you using a physics engine? Most should allow you to set up these requirements so you'll be much better off using a physics engine rather than trying to figure it out yourself.

[jontan6]

Hey,

I've a question: Probably most of you, know what the Coefficient of Friction is.

Well, currently I am working on a racegame and now I want to implement physics - but there should be different materials, on the one side different materials for the tires and different street materials.

I don't want to define the coefficient of friction for the friction between all materials, but I thought it should be possible to have one value for the street and one for the tire and then to calculate the coefficient of friction from the two values.

Is there such a unit in physics, which describes the roughness of one material?
If not, what do you suggest to do?

Thanks a lot
D.

i think first you need to research which physics engine u want to use and then figure out how to do stuff in that engine

[rogerborg]

AFAIK, coefficients are always between two materials. However, since you're really only interested in the coefficient between ground surfaces and various types of rubber, I'd suggest that you'd get good results from defining a base coefficent for the ground surfaces - possibly once for each gross category of tyre - and have each tyre apply a multiplier based on its quality.

Actually, I'd suggest 4 coefficients for each surface: fully dry and fully wet coefficients for fully slick and fully grooved tyres. Then find the actual coefficient by multiplying each coefficient by the wetness / inverse wetness and how slick or grooved the tyre is, e.g. if it's 25% wet and the tyre is 33% grooved, and has a 10% 'grip bonus', then the total coefficient is:

μTotal = ((μWetSlick * .25 * .667) + (μDrySlick * .75 * .667) + (μWetGrooved * .25 * .333) + (μDryGrooved * .75 * .333)) * 1.1

[arras]

The friction is the roughness isn't it?

It isn't. Very rough surfaces can have low friction in specific conditions. Take shark's skin in water for example.

[JP]

I've never touched sharks skin so i'll take your word on it being rough! But isn't the water's complete lack of roughness the reason there's no friction?

I don't know... i'm probably in over my head here anyway, physics wasn't my strongest point at school! Mind you... I could put that down to the teacher... he was the most awesome and funniest teacher ever... and as you can imagine that meant he was actually the worst teacher ever No respect there!

[rogerborg]

I've never touched sharks skin so i'll take your word on it being rough! But isn't the water's complete lack of roughness the reason there's no friction?

Shark skin is covered in tiny teeth-like structures, and can be used as a primitive form of sandpaper. Remove from the shark first.

The structures reduce friction with the water in front of shark, and increase it with the water behind. Friction coefficients are empirical and highly dependent on circumstances, which is what makes them a real bugger to calculate and simulate.

[JP]

The true hardcore leave the skin on the shark and use it for sandpaper as-is. I thought you were hardcore too rogerborg... what a let down...

[Dorth]

He was telling YOU how to do it... When he does it, he does so naked while making love to a bound Hannigan, debating a dozen university deans, solving world crisis and using 5 living sharks at the same time.

On his sick day. Which he doesn't have, 'cuz he only performs at awesome!




(And that was my 500th post. A gift to Rogerborg, how appropriate ^^ )

[JP]

This forum is heading straight into the gutter with all this sort of naughty talk... and i blame rogerborg for bringing up alyson hannigan fetishes in the first place!

[Dark_Kilauea]

It's too late, Rogerborg is an irrlicht developer now. This forum is already in the gutter for good.

[arras]

But isn't the water's complete lack of roughness the reason there's no friction?

Every material have its "roughness", liquids and gases included. And they of course have their friction. I put roughness in quotes here since its not the term which is used in this case but principle is the same.

The true hardcore leave the skin on the shark and use it for sandpaper as-is

You have to dry it before you wan to use it as sandpaper which mostly requires you to remove it from shark first. But true is, there are some bodyparts which can be used as-are. Tail for example. That of course require them to be removed from shark in turn

It's too late, Rogerborg is an irrlicht developer now.

Seems I missed a lot since I visit this place so seldom Congratulation Rogerborg