1. WORK
What does work mean in Physics?

2. LEARNING OUTCOMES
 Recall and apply the relationship
Work done = Force × Distance moved

3. LOOKING BACK...
 Kinematics – describing motion of objects
precisely
 Distance/displacement travelled
 Speed/velocity
 Acceleration
 Forces – explains what causes objects to
change its state of motion
 Balanced forces
 Unbalanced forces

4. WORK DONE
 Compare pushing an object (applying a
force) over different distances
 1 m
 1 km
 Which uses more energy?

5. WORK DONE
 Work is done when a constant force
produces motion
 The amount of work done on an object
depends on
 The magnitude of the force, F, that is
applied
 The distance, d, travelled in the direction
of the force

6. UNITS OF WORK DONE
 The SI unit of work is Joule (J).
 One joule of work is done when
 A force of one Newton moves an object
 Through a distance of one meter in the same
direction of the force

7. THINK!
 Is work done a scalar or a vector?
 Recall:
 Work done = Force x Distance moved in the
direction of the force
 Work done is a scalar.

8. THINK!
 If we push hard against a wall (force
applied), is there work done?
 No work is done unless a force causes an
object to move!

9. CASE STUDY: WEIGHTLIFTER
 Is there work done
 Lifting the weight up from the ground?
 Holding it there?

10. WORK DONE VS. GETTING
TIRED
 A person gets tired supporting a weight
at a constant height even though no work
is being done.
 No work is done against gravity when the
weight is at the same height.
 Even though no work is done when the
weight or suitcase is held, a force is still
needed to act on the object to balance its
weight. Hence, one still feels tired.

11. POWER
What are some of the various
forms of energy that you know
about?

12. LEARNING OUTCOMES
 Recall and apply the relationship
Power = Work done ÷ Time taken
 Calculate the efficiency of an energy
conversion using the formula Efficiency =
Useful energy output ÷ Total energy input

13. POWER
Mercedes Benz Chery QQ

14. POWER
 Which car is more powerful?
 What can the more powerful car do?
 Accelerate faster
 In other words, a more powerful car can
do more work in gaining kinetic energy at
a faster rate

15. POWER
 Power is defined as the rate of doing
work
 Unit of power is Watt (W)
 1 Joule per second (J/s)

16. POWER
 Alternative formula:
Power = work done / time
Recall: work done = force x distance
P = (F x s) / t
Recall: velocity = displacement / time
P = F v