1. FRICTION Aim: How do different surfaces affect the amount of friction?

2. Friction FRICTION – The force that causes two surfaces to stick together Even between two smooth surfaces, like a hockey puck on ice, the two surfaces are full of hills and valleys

3. Normal Force Units: Newtons (N) In most cases… Friction Formula Force of Friction Units: Newtons (N) Coefficient of Friction Units: UNITLESS!!!

4. Coefficient of Friction Represented by the Greek letter: µ (mu) Describes how much two surface stick together Different materials have different coefficients The higher the coefficient, the more two surfaces stick together Typically between 0.0 and 1.0

5. Two Types of Friction Static Friction– µ s STATIONARY Objects Keeps objects in place In order to break an object free from the surface, the force must EQUAL the static friction first! Kinetic Friction– µ k MOVING Objects Opposes motion

6. Static Friction > Kinetic Friction Static Friction Kinetic Friction

7. BE CAREFUL!!! Pay attention to the type of MATERIALS and if the object is STATIONARY or MOVING The coefficient of friction will vary depending on the situation and material FIND ME!!!

8. Example #1 A 15kg wooden block is stationary on a wooden table. (a) Determine the amount of static friction between the block and table. (b) What minimum force is necessary to start the block moving to the right? FNFN FgFg 61.8N FfFf

9. Example #2 A 60kg skier glides at a constant speed across flat level snow. What is the kinetic friction between the skis and the snow? b.How much force is necessary to keep going at constant speed?

10. Example #3 A 0.4kg hockey puck is passed from one player to another with a force of two Newtons. Determine the initial acceleration of the puck.

11. Example #4 Tom Cruise (67kg) slides with an initial speed of 2.1m/s and comes to a stop in 1.2 seconds. Calculate the force of friction between his socks and the floor.

12. P.S.… What form of energy results from friction?

13. Summary Which letter represents the coefficient of friction? What are the units for the coefficient of friction? Where can you find a table for different coefficients of friction? Describe the two types of friction List two factors that affect friction