1. Exploring Frictional Forces
Friction and Newton’s Laws
Static and Kinetic Friction
Coefficient of Friction
Practice

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3. Friction
The analysis of friction is very important to practical situations since friction is present everywhere.
Friction is a good and bad thing.
Good when our tires meet the pavement
Bad when reducing efficiency and/or producing heat
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4. Friction Friction always opposes motion (or Fnet) Kinetic friction
Static friction
Air resistance

5. Friction and Newton’s Laws
Friction is simply a force included and accounted for in a FBD.
Applies to situations where:
Fnet = 0
Fnet = ma

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7. Static Friction
The magnitude of the force needed to start a stationary object moving is the maximum static friction, FSmax

8. Kinetic friction Kinetic friction acts on any object that is in motion
The magnitude of the force needed to keep the …………….

9. Coefficients of Friction
The coefficient of friction is a ratio of the magnitude of the force of friction between two surfaces to the normal force between those surfaces.

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11. Check Your Understanding
A crate of fish of mass 18.0 kg rests on the floor of a parked delivery truck. The coefficients of friction ……………….
a horizontal force of 75.0 N [E] is applied to the crate?
if a horizontal force of 95.0 N [E] is applied?
Answers: a) No movement because the Fapp < Fs b) FK = 72.3 N [backwards], a = 1.26 m/s2

12. Check Your Understanding
A musician applies a horizontal force of 17 N [W] to an instrument case of mass 5.1 kg. The case slides across a table with an acceleration of 0.39 m/s2 [W]. What is the coefficient of kinetic friction between the case and the table? Answer: μK = 0.30