Friction and braking

Question 1

What is friction?

Answer 1

Friction is the force between interacting surfaces that hinders their relative tangential motion

Question 2

Can the deformation of the contacting surface play a small role in friction?

Answer 2

Deformation of the contacting surface might play a small role, but is usually neglected

Question 3

Is the speed of motion important for friction?

Answer 3

The speed of motion can be important – static friction force usually exceeds dynamic friction force for a given case

Question 4

Friction is influenced by:

Answer 4

1. Geometry of the surfaces
2. Surface properties (elasticity, roughness)
3. Running conditions: normal pressure, vibration, temperature
4. Lubrication/Lubricants

Question 5

Draw a basic friction model

Answer 5

1. 1 Degree of freedom model can be used to investigate sliding and oscillating contacts. (page 3)
2. The wall (left side) and the mass (m) are both able to move horizontally
3. Assume a spring constant k
4. The net force in the spring depends on its extension, which depends on displacement of both its ends.
5. The friction resisting motion of the
   block of mass m is F
6. Newton’s law of motion

Question 6

What is the most common model of friction?

Answer 6

The Coulomb friction model