1. Force, Work and Power
Chapter 40

2. Force
A force is anything which causes an object to move or change direction.
Forces are measured in Newtons (N)
Examples of Force:
-Push
-Friction
-Pull
-Electric
-Weight
-Magnetic

3. Friction
Friction is the force which prevents easy movement between two objects in contact.
Friction occurs between rough surfaces.
NB if we look very very closely all surfaces are rough.

4. Friction
High Friction:
Low Friction:

5. Reducing Friction Lubricants can be added to reduce friction.
Examples of lubricants are oil, grease and synoval fluid.

6. Weight The weight of an object is the pull of gravity on it.
Weight is a force measured in Newtons.
Do not confuse weight and mass.

7. The Effect of Force on a Spring
Hooke’s Law: The extension of a spring is in direct proportion to the force acting on it.
(Adding equal weights to a spring will increase the extension by equal amounts)
NB if too much weight is added the spring will reach its ‘‘elastic limit’’
and Hooke’s law will no longer apply

8. Hooke’s Law

9. Application of Hooke’s Law
Forces can be measured using a spring balance.
The greater the force the more the spring is stretched.

10. Work Work is when a force moves an object.
Work is measured in Joules (J)
Work = Force (N) x Distance (m)
Examples of Work
A pushing a trolley
running

11. Work
Example:
A force of 10 Newtons is being moved 20m calculate the work done.
Work = Force x Distance
Work = 10N x 20m
Work = 200J

12. Power Power is the rate at which work is done.
Power is measured in watts (W)
1 W = 1J/s

13. Power
A weightlifter lifts a weight of 120kg to 2m in a time of 3 seconds calculate the average power.