2. The origin of friction…
This roughness is unpredictable
and definitely nonlinear!

3. v f There are two kinds of friction Kinetic
when the surfaces are slipping past each other v f
Kinetic friction always opposes the relative motion

4. v f v = 0 f Fext There are two kinds of friction Kinetic
when the surfaces are slipping past each other v f
Kinetic friction always opposes the relative motion
v = 0
Static
when the surfaces are not slipping f
Fext
Static friction opposes the force that is trying to slide the objects

5. This is our model of kinetic friction
Kinetic friction is proportional to the normal force between the two objects:
This is our model of kinetic friction

6. When you slide a 50.0 g salt shaker to your friend at the other side of the table, you give it an initial speed of 1.15 m/s. The salt shaker comes to rest in m. Assume constant acceleration.
What is the coefficient of kinetic friction between the shaker and the table?

7. When you slide a 50.0 g salt shaker to your friend at the other side of the table, you give it an initial speed of 1.15 m/s. The salt shaker comes to rest in m. Assume constant acceleration.
What is the coefficient of kinetic friction between the shaker and the table?
For how much time does the salt shaker slide before coming to rest?

9. A copper block, starting from rest, slides down an inclined steel ramp that is 75 cm long. The ramp is inclined 42º to the horizontal. What is the block’s speed when it reaches the bottom of the ramp?

10. Static Friction

11. Static Friction

13. As you drive down a dry road (doing the speed limit, of course) is the friction between your tires and the road static friction or kinetic friction?
Static
Kinetic
There’s no way to tell

14. Tension in a rope or string
Molecular forces in a string that is stretched pull back towards the middle
The molecules resist being torn apart
Ropes always PULL
(They transmit force from one object to another)

15. The tension in a rope is the same everywhere in a rope

16. NOTE:
Ideal pulley
Ideal rope