Section 2.2 – Newton’s Laws Friction

PROS  We need friction to move. CONS  Friction causes production of heat, loss of mechanical energy, and general wear and tear on the object. Friction is the Jekyll and Hyde of forces.

Microscopic details of the force of friction are still not properly understood. CURRENT THEORY  Even the most polished surfaces are rough microscopically  Two objects in contact make connections at their surfaces  Intermolecular forces form  These welds must be for the object to move

types of material in contact normal force exerted by one object on the other The magnitude of the frictional force is determined by the

Combining these components that make up the frictional force we obtain

 The theory of frictional forces states that an object at rest experiences friction than when it is already moving.  This is because it is harder to form microscopic welds when the object it moving across a surface than when it is stationary.

 In general, the force of friction acts opposite to the direction of the object’s motion.

See the following for extra practice…  Example 8 on Page 173 of your text  Example 9 on Page 174 of your text  Example 12 on Page 177 of your text