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Here is my question:

should the kinetic friction coefficient Fk be the same when the object with mass m is pulled with a constant velocity as the kinetic friction coefficient with the same mass m when it was pushed and released.

The measurements in the second case were taken from the decelerating part of the Force vs. Time graph.

I have several table with data many of which i have calculated myself.

from the formula: Fk = ;mu * Fn

Fk - kinetik friction force,

;mu - coefficient of friction kinetic force

Fn - normal force

in the first case I have:

m = 0.09 kg

Fk = 0.1387 N (the uncertainty here is 17% !!! Fk = 0.1387 +- 0.0238)

Fn = 0.882 N

=> ;mu = 0.1573

In the second case:

m = 0.09 kg

Fk = 0.2585 N

Fn = 0.882 N

=> ;mu = 0.2931

here i also have uncertainty in acceleration which I use in order to find Fk.

So, my question is: Should the coefficient ;mu be different in two cases or do I have such a big error?

THANKS!!