WORKWhat does work mean in Physics?

LEARNING OUTCOMES Recall and apply the relationship

Work done = Force × Distance moved

LOOKING BACK... Kinematics – describing motion of

objects preciselyDistance/displacement travelledSpeed/velocityAcceleration

Forces – explains what causes objects to change its state of motionBalanced forcesUnbalanced forces

WORK DONE Compare pushing an object (applying a

force) over different distances1 m1 km

Which uses more energy?

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

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

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.

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!

CASE STUDY: WEIGHTLIFTER

Is there work doneLifting the weight up from the ground?Holding it there?

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.

POWERWhat are some of the various forms of energy that you know about?

LEARNING OUTCOMESRecall and apply the relationship

Power = Work done ÷ Time takenCalculate the efficiency of an energy

conversion using the formula Efficiency = Useful energy output ÷ Total energy input

POWERMercedes Benz Chery QQ

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

POWER Power is defined as the rate of doing

work Unit of power is Watt (W)

1 Joule per second (J/s)

POWER Alternative formula:

Power = work done / timeRecall: work done = force x distance

P = (F x s) / tRecall: velocity = displacement / time

P = F v