Transcript Power - science

17 July 2015
Power and electrical power
Objectives
Understand what power is and be able to calculate it.
HSW: AF5 – Working critically with evidence
AF4 – Using investigative approaches
Used before in: lesson 1 – work
Will use again in:
PLTS: Team workers – Work collaboratively with others.
Used before in: Science A
Will use again in:
Keywords: Power, Energy, Weight, Force
Outcomes
• All students should be able to describe
what makes an object powerful or not.
• Most students should be able to define
power and use the equation.
• Some students should be able to
evaluate practical work and describe how
to make it more valid and reliable.
Powerful cranes
Which is the most powerful crane? Explain why.
How is power calculated?
The power exerted by an object can be calculated using one of two equations:
power =
work done
time taken
 Work done is measured in joules (J).
 Time is measured in seconds (s).
 Power is measured in watts (W).
Remember that work done = energy transferred.
Calculating power question 1
A lawnmower engine does 10
kJ of work in 10 seconds.
What is the power of the
engine?
power =
work done
time
= 10,000 / 10
= 1,000 W = 1 kW
Calculating power question 2
A car transfers 12 mJ of energy
in 2 minutes. What is the
power of the car?
power =
work done
time
=
= 12,000,000 / 120
= 100,000 W = 100 kW
energy transfer
time
Power, work and time
calculations
Anagrams
And finally – we find out – who are
more powerful – boys or girls?
• Force x distance = energy
• Energy/time = power
Boys:
Force
Dist
for 1
rep
reps
Total
dist
Girls:
work
time
power
Force
Skipping
Lifting
Push ups
Analysis: What conclusion can you draw?
Evaluation: was the evidence reliable? Explain.
Dist
for 1
rep
reps
Total
dist
work
time
power
Energy
Gravitational
Watts
Heat
Power
Kinetic
Electrical
1 Joule per
second
Joules
Plenary - Multiple-choice quiz