1. Friction

2. Static and Kinetic Friction
There are two types of friction. Both ALWAYS oppose motion.
Kinetic friction is exerted on one surface by another when the two surfaces rub against each other because one or both of them are moving.

3. Static and Kinetic Friction
Static friction is the force exerted on one surface by another when there is no motion between the two surfaces.

4. Kinetic Friction Force
Ff, kinetic = μkFN
μk = coefficient of kinetic friction

5. Static Friction Force Ff, static ≤ μsFN
μs = coefficient of static friction

6. Practice
You push a 25.0 kg wooden box across a wooden floor at a constant speed of 1.0 m/s. How much force do you exert on the box.

7. Practice
#s 1-3 pg 145

8. Practice
A student moves a box of books by attaching a rope to the box and pulling with a force of 90N at an angle of 30. The box of books has a mass of 20kg, and the coefficient of kinetic friction between the bottom of the box and the sidewalk is .5m. Find the acceleration of the box.

9. Practice
Given:
m = 20kg
uk = .5
Fapplied = 90N at 30°
Find a

10. Practice
#s 1-4 on pg 147