1. Chapter4 RESISTANCE

2. Friction Forces Friction - a force that opposes motion of two solids or a solid and a fluid Static Friction (F static ) - a force required to start relative motion between two objects Kinetic Friction (F kinetic ) - the force required to maintain a constant speed between two surfaces in contact

3. WHAT CAN BE DONE TO DECREASE THE AMOUNT OF FRICTION EXPERIENCED BY TWO OBJECTS?

4. Static friction is usually greater than the kinetic friction. This is due in part as a result of how hard the surfaces are pressed together. This is called the normal force (F N )

5. Coefficient of Friction ( μ ) The ratio of maximum force (static or kinetic) of friction to the normal force between the two surfaces in contact.

6. Surface μSμS μKμK Wood on wood0.50.2 Wood on concrete0.60.4 Rubber on dry concrete0.80.7 Rubber on wet concrete0.650.57 Steel on steel (dry)0.780.58 Steel on steel (oiled)0.110.05 Steel on Teflon0.04

7. Lab Preview A spring scale will be used to determine the pulling force required to get the sled to move?

8. Determining Kinetic Coefficients of Friction

9. Lab Preview SurfaceMass of Sled (kg) Mass Added (kg) Total Mass (kg) Weight of Sled and Mass (Newtons) Ivory on Dry Metal 0.08.250

10. Lab Preview SurfaceKinetic Friction Force Normal ForceCoefficient of Kinetic Friction Ivory on Dry Material 0.422.53 μ K = (Kinetic Friction Force) / Normal Force