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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