4.3 Power
is the rate at which work is done.
Power
can be calculated from work and time
· Power The rate at which you do
work
· Common
meanings of the word power :

Source of energy (power plant)

Strength (powerful engine)
· Scientific
definition of power Doing work over a period of time
Calculating
power from work
· To find
power, divide the amount of work by the time it takes to do the work
Power= Work
time
P= W
t
· Watt Unit of measurement for power
· Watt= One
joule of work done in one second
· Measured
in watts or kilowatts
Horsepower
· The amount
of work a horse can do in one minute
· Read page 132 for
background on Charles Watt
Power
can be calculated from energy and time
· Power= Energy P= E
time t
· You can
think about power as any kind of transfer of energy in a certain amount of time
· Also
measured in watts
(joules per second)
Everyday
power
· Many
appliances rely on electricity for energy
· How does a clothes dryer work?
Practice
Problems
1. An Antarctic explorer uses 6000J of work to pull his sled
for 60s. What power does he need? See page 132 for the
answer
2. A light bulb used 600J of energy in 6s. What is the power of the light bulb? See page 134 for the
answer