DYNAMICS II

FRICTION

• To start something moving we have to overcome the force of static friction.

The maximum value for fs, the force of static friction, is m s, the coefficient of static friction, times N, where N is the magnitude of the Normal force.

fs < m sN

• When sliding begins, the frictional force decreases. The magnitude of the force of kinetic friction is fk = m kN
• Frictional forces oppose the motion and act opposite to the direction of motion.

EXAMPLES

• A block which weighs 100 N is on an inclined plane where the angle of inclination can be adjusted. If the coefficient of kinetic friction is 0.50, what is the angle of inclination when the block slides down the incline at constant speed?

• Three blocks are connected by cords which are placed over pulleys as shown in the figure which will be given in lecture. Block A has a mass of 2.0 kg, block B has a mass of 20 kg, and the coefficient of kinetic friction is 0.10.
• What is the mass of block C if the acceleration of B is 2.0 m/s2 to the right?
• What is the tension in each cord?

• An object is placed into uniform circular motion with a vertical plane. What is the tension in the rope?