Friction

Question 1

Friction is…

Answer 1

the force at the interface of two surfaces. It opposes motion.

Bonds formed between the two surfaces.

Question 2

If objects are stationary, friction equals…

Answer 2

the sum of all forces that would produce movement.

Question 3

If objects are moving, friction is…

Answer 3

less than the sum of all forces that would produce movement.

Question 4

Amount of force required to cause initial movement?

Answer 4

Static friction

Force of static friction is always higher than rolling or sliding friction.

Question 5

Amount of force required to maintain movement?

Answer 5

Sliding or rolling friction

Bonds formed between stationary surfaces form less frequently in motion.

Question 6

Two factors affecting friction…

Answer 6

1) Normal reaction force (R): if greater forces pressing two surfaces together, more friction.
2) Coefficient of friction (u): describes the surface characteristics - number of bonds formed.

Therefore, Ff = uR

Question 7

What is the force required to push a bobsled from a stationary start?

u = 0.05
m = 150kg (1500N)

Answer 7

Ff = uR

Ff = 0.05 x 1500

Ff = 75N

Question 8

How can we test for friction?

Answer 8

1) Spring scale to measure force required to move, or continue to move, an object across a surface.
2) Use a force platform to measure forces under specific conditions (horizontal force / vertical force)

Question 9

Where do we use info on friction?

Answer 9

Design of netball, basketball, hiking, running shoes, etc

Design of playing surfaces - effects of temperature, moisture, etc

Motor racing (tyres) - compound effects

Engineering of testing equipment, resistance training machines, engines, etc

Bat/club faces (draw on golf shot), shoe surfaces (swerve on soccer kick), racquet strings, etc