Im trying to add friction to my physics engine.

I know:

-The collision point and normal

-Properties of both bodies:

*Center of mass

*mass, inertia

*angular and linear velocity

*angular and linear forces

So, how would i go about implementing friction?

Currently i am able to apply a force to a point on a body (which translates to linear force and torque)

I am able to do friction for surface on surface (its a top down 2d game) where i assume the other surface to have infinite mass. However this directly modifies the velocity and im not sure how to translate that to friction from collisions.

The internet didnt seem very helpful on this one, anyone care to explain how to make it all work? Preferably in a way that works smoothly and wont estimate the forces wrong and cause everything to explode.

I tried to use my getDeltaVelocityCuzOfFriction(VelocityDifference, frictionCoeff, normalForce) method but since i dont have a method of setting force directly at a point on the body, and i dont know how to get the normal force, i couldnt get it to work. There might be other problems with my collision response that cause it to not work but i cant be sure until i know the friction itself should work.

Thanks.

I cant simplify it much since this isnt a platformer - there are no static parts.

I will make a "set velocity at point x" method and work with velocity instead of forces because that seemed to work for the simpler case.

I still need to find out how to find force of contact (ignoring gravity) and how to make it so that if a big and small object have friction between them, the big one wont move as much as the small one... hm.

F = ma

I still need to find out how to find force of contact (ignoring gravity) and how to make it so that if a big and small object have friction between them, the big one wont move as much as the small one... hm.

that's impulse and momentum and conservation of momentum, not friction. 1st year mechanics. any decent college physics book will have the info.

as i recall, m1*v1+m2*v2 (inital - before collision) = m1*v1+m2*v2 (final - after collision). or something like that, better look it up. <g>.

friction is a totally different set of physics formulas.

with friction, the variables are mass, velocity (? been a long time), and Ks or Kd, the coefficient of static or dynamic friction, depending on whether you're sliding/skidding (dynamic) or not (static). Ks and Kd are constants that are empirically derived for two given surfaces (such as tire rubber and asphalt, ice on ice [which is about the lowest], etc). the exact values of Ks and Kd are different for any 2 given surfaces. but they all follow the general rule that Ks is higher than Kd (or is it always lower? <g> another one you'dd better look up). Ks and Kd essentially define the points at which you lose and regain traction, based on the speed, vehicle weight, and the type of friction surfaces.

as i recall, m1*v1+m2*v2 (inital - before collision) = m1*v1+m2*v2 (final - after collision). or something like that, better look it up. <g>.

I have that part correct, friction should work correctly at relatively high tangential (?) velocities.

However, the problem is, that at low velocities the fricition froce will be too high which causes it to reverse the direction of the tangential velocity which causes jitter, and at high velocities, more serious unstability.

As i understand it i need to find the force that would reverse the direction of the velocity and clamp the friction impulse to that (so if the impulse is too high, itll just zero out the relative tangential velocity instead of reversing its direction)

I just need some guidance as to how to find that maximum impulse, preferrably something that also works in multiple body systems (some kind of iterative solver thingie?)

I will attempt to find the maximum impulse for a single contact (ignoring multiple simultaneous contacts)