1. Friction

2. Friction?

3. What is friction?
Friction is the force resisting the relative motion of solid surfaces sliding against each other.

4. What is the coefficient of friction?
Show to the right is a free body diagram (also known as a force diagram).
There is no net force acting on the object.
Therefore it has no acceleration.

5. What is the coefficient of friction?
The coefficient of friction is the ratio of the force of friction to the normal force.

6. What is the coefficient of friction?
The coefficient of friction only depends on how rough the two surfaces in contact are.
The rougher the surfaces, the higher the coefficient.

7. What is the coefficient of friction?
A coefficient equal to 0.61 (aluminium on steel) tells us that the frictional force is 61% of the normal force.
For ice on ice the frictional force is just 10% of the normal force.

8. Large or small coefficient?

9. How do we calculate the force of friction?
The equation can be rewritten as shown.
This equation shows us that the only factors that determine friction are the roughness of the surfaces and the normal force

10. How do we calculate the force of friction?
If we know the normal force and the coefficient of friction, we can calculate the force of friction.