1. Frictional Forces This topic may be abrasive

2. Friction Friction is a force that opposes motion Friction will cause a moving object to slow down and finally stop. If ANY two objects are touching, there is friction!!!!

3. Friction

4. Types of Friction Sliding Friction – occurs when object slide over each other. Example: Sliding your chair back and forth Rolling Friction – Produced by objects such as wheels or ball bearings. Example: A car going down the road or a cart being pushed down the hallway

5. Kinetic friction: the friction experienced by surfaces sliding against one another Static friction: force depends on the normal force:

6. Kinetic Friction Moving Friction The constant μ k is called the coefficient of kinetic friction.

7. Kinetic Friction

8. The kinetic frictional force is also independent of the relative speed of the surfaces, and of their area of contact.

9. Low Load High Load Elastic deformation

10. Static Friction The static frictional force keeps an object from starting to move when a force is applied. The constant μ s is called the coefficient of static friction. The static frictional force has a maximum value, but may take on any value from zero to the maximum

11. Static Friction

12. Static Frictional Force

13. Static Friction The static frictional force is also independent of the area of contact and the relative speed of the surfaces

14. 2

15. Question? A desk has a mass of 27.5 kilograms. If the coefficient of static friction between the desk and the floor is 0.44, what force must be used to move the desk from rest? f s = μ s N N = m *g =.44 * (27.5*9.8) = 118.6N

16. Question Once the desk above is in motion, what force must be used to keep it moving at a constant velocity if the coefficient of kinetic friction is 0.293 F N = (m*g) F N = (27.5*9.8) f s = μ k F N =.293 * ( 9.8*27.3) = 78N

17. Extra Question 3) An object takes 12.3 meters to stop because of friction. Assume no skidding. If the coefficient of static friction is 0.44, what is the initial velocity of the object?

19. A ninja of mass 70 kg is at rest on a ramp with slope of 75 degrees. What is the frictional force applied to the ninja? 70 degrees Are we dealing with static friction or kinetic friction? Remember: fs = μ s N

20. Free Body Diagram 70

21. Lab Purpose: find the force of static friction acting upon your object and coefficient of static friction Materials: Protractor, ramp, object Be sure to include a free body diagram, 5 trails in which you average your measured max angles, data analysis, and RERUNN conclusion