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Work, Power and Efficiency

The document explains the concepts of work, power, and efficiency, defining work as the energy transferred when a force moves an object over a distance, measured in joules. It provides the formula for calculating work done (W = F x d) and introduces power as the rate of energy transfer, calculated using the formula Power = work done / time. Examples illustrate how to compute work and power, demonstrating the differences in power between two individuals performing the same task at different speeds.

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17 views2 pages

Work, Power and Efficiency

The document explains the concepts of work, power, and efficiency, defining work as the energy transferred when a force moves an object over a distance, measured in joules. It provides the formula for calculating work done (W = F x d) and introduces power as the rate of energy transfer, calculated using the formula Power = work done / time. Examples illustrate how to compute work and power, demonstrating the differences in power between two individuals performing the same task at different speeds.

Uploaded by

amber.yuhan0513
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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Download as DOCX, PDF, TXT or read online on Scribd
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Work, power and efficiency

Energy and work


 When a force causes a body to move, work is being done by the
force. Work is the measure of the energy transferred when the force
(F) moves an object through a distance (d).
 When the work is done, energy has been transferred from an energy
store to another so:
 energy transferred = work done
 both of these are measured in joules (J)

Calculating the work done


 the amount of work done depends on the size of the force and the
distance in which the object travelled caused by the force.
 The equation used to calculate the work done is:
 Work done = force x distance (W = F x d)
 This is when work is measured in joules (J), Force is in newtos (N)
and distance is travelling the same direction as the force and is
measured in metres (m)
 For example :

15N force applied and box moved by 3m

 In this example, a force of 15N causes the box move a distance of


3m so:
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 W=Fxd
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 W = 15 x 2
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 W = 30 J
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 One joule of work done when a force of one newton is used to
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move an object a metre.

Energy and Power


 When work is done on an object, energy is transferred. The rate
that the energy is being transferred is called power.
 So the more powerful something is, the faster it’ll transfer energy.

How to calculate Power


 The equation for calculating power is:
 Power = work done / time
 Power = W / t
 This is when power (P) is measured in watts (W), work done (W) is
measured in joules (J) & time is measured in seconds (s).
 One watt = one joule per second (J/s). So every extra joule
transferred the power increases by a watt.

For Example:
 2 cats (Bob & Timmy) lift a 2N weight
through a vertical height of 10m.
 Bob takes 5 seconds. Timmy takes 10
seconds.
 Work done: W = F x d = 2 x 10 = 20 J
 Bob： P = W / t = 20 / 5 = 4 W
 Timmy: P = W / t = 20 / 10 = 2 W
 In conclusion since Bob did it twice as
fast as Timmy, Bob is more powerful than
Timmy.

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