# Friction: Force and Mass

Where F s, max is the maxixmum force of static friction. Once the external force overcomes static friction, the object moves. Its motion is opposed by kinetic friction. The force of kinetic friction is given by f k = ukN where u k is the coefficient of kinetic friction. Therefore , the coefficient of kinetic friction is given by Uk = fk/n

A diagram of the experimental setup is shown in the figure at the right. Of interest is the friction between the block and the tabletop. An external pulling force is provided by the weight hanging on the end of a string which is adjusted to balance the force of friction. The free- body diagram of the block is shown in the figure at the left. The free body diagram of the pulling mass is shown in the figure on the right. The equations for the forces on the block in the x- and y- directions are written as EF x = 0 = T – F

EF y = 0 = N – m

Where T is the tension in the string, f is the force of friction, N is the normal force exerted on the block by the tabletop, and m is the total mass supported by the tabletop. The equation for the forces acting on the pulling mass is written as EF = 0 = mp – T

Thus, the force of friction f is equal to the pulling mass mp. The normal force N is given by N = m = mb + m added

Where mb is the mass of the block...

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