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What units are the physics material in?
I have two spheres colliding. I'm trying to match the velocity profile (velocity decay due to friction) to a real-world collision. I have the values from dynamic friction and static friction from the real-world data in meters per second (m/s).
Are the dynamic frictions and static friction in the physics material settings in meters per second?
Answer by PatientVoid · Jul 15, 2020 at 01:35 PM
Okay, answering my own question. Turns out, they are unitless values. So I'd have to convert the real world values to unitless values for them to match.
Friction is coefficient of friction, "mu" (μ).
Personally, I have never seen friction expressed in m/s (which is a velocity). How can a velocity be interpreted as friction?
@Edy The rate of change of velocity (acceleration) can be equated to mu times gravitational acceleration. I have the acceleration of a ball and the gravity constant, but missing mu. Therefore if I divide acceleration of ball with the acceleration of gravity, it'd equal to mu. The units cancel out and thus the coefficient of friction is unitless.
I was forgetting to divide by gravity and thus had mu *9.81m/s^-2, thus the units.
@Edy I think friction is typically in newtons in real world physics
Friction force is Newtons. But coefficient of friction is a unitless value, "mu" (μ). Friction force (newtons) equals coefficient of friction (unitless) times normal force (newtons).