1. What is the deal with friction?

2. Friction Force that opposes the motion of objects that touch as they move past each other. 4 types of friction –Static –Sliding (kinetic) –Rolling –Fluid

3. Static Friction Friction force that acts on objects that are not moving. In this picture, F frict = F app so the net acceleration = 0.

4. Sliding Friction (Kinetic) Force that opposes the direction of motion of an object as it slides over a surface. In this picture, F frict < F app so there is a net acceleration to the right.

5. Coefficient of Friction Measure of the strength of friction between two surfaces. A coefficient of 1 means the force of friction is equal to the force holding the surfaces together. A coefficient of 0 means there is no friction.

6. Coefficient of static friction  s is the coefficient of static friction.  s is a dimensionless quantity (no units) which is specific to different materials. F frict(max) =  s F norm F norm is the normal force F frict is the force due to friction

7. Coefficient of sliding friction  slide is the coefficient of sliding friction.  slide is a dimensionless quantity which is specific to different materials. F frict =  slide F norm

8. Common values of  s and  slide  s  slide Steel on steel 0.740.57 Glass on glass 0.940.4 Rubber on concrete 0.80.65 Ice on ice0.10.03

9. Rolling Friction Friction force that acts on rolling objects, caused by the change in shape at the point of rolling contact. Rolling friction is much less than static and sliding friction. That’s why wheels make it easier to move heavy objects.

10. Fluid Friction Force that opposes the motion of an object through a fluid. Fluid friction increases as the speed of the object through the fluid increases. Air Resistance = fluid friction acting on an object moving through air.

11. Falling Objects Gravity = Force that acts between any two masses. Gravity is an attractive force. Earth’s gravity acts downward toward the center of Earth. Gravitational force depends on mass.

12. Terminal Velocity Constant velocity of a falling object when the force of air resistance (also known as a drag force) equals the force of gravity. When an object reaches terminal velocity, the net force = 0 so the acceleration = 0. See pages 370-371

13. Projectile Motion Motion of a falling object after it has been given an initial forward velocity.