1. Textbook: 5.5 Homework: WS - Friction

2. Coefficients of friction, μ
The coefficient of friction is the ratio of the magnitude of the force of friction to the magnitude of the normal force.
The value for the coefficient of friction depends on the nature of the two surfaces in contact and the type of friction—static or kinetic.
Coefficient of Static Friction
Coefficient of Kinetic Friction

4. Friction
Friction is the force that stops two surfaces from sliding across each other
It depends on:
The two surfaces
The force pressing them together

5. Static vs. Kinetic
Static Friction (SFN): The maximum force that stops an object from moving
Fs = SFN
Kinetic Friction (kFN): The minimum force necessary to keep something moving Fk = kFN
Pg. 183 #41, 42, 48

6. Ex 1.
What is the minimum force needed to move a 2000 kg car on asphalt from rest?
What is the acceleration of the car if the same force was continuing to apply to the car?

7. Pg 183 # 38/40. A sled of mass 26 kg has an 18 kg child on it
Pg 183 # 38/40. A sled of mass 26 kg has an 18 kg child on it. The big brother is pulling with a force 30 N to the right and 10 N up; and the big sister is pushing at 40 N right and 16 N down. Given μk = Calculate:
a) the normal force FBD:
b) the force of friction.
c) the acceleration of the sled and child.