As a store manager, would
you prefer to hire a clerk
who could unload a truck
in one hour, or a second
clerk that could unload a
truck in half an hour?
If the employees did the
same amount of work
unloading the truck, what
was the difference?
Time
Power – is the rate at
which work is done
In other words, how fast
or slow is the work done
Watt is the unit for power
1 watt is equal to 1 joule of
work done in 1 second
Make note of units, if time is not in
seconds, it must be converted.
Remember that W=Fd, so P=
If
, then P=F*v.
(F*d)
t
.
In physics, when you see
the word power you
should think: power is the
energy used by the time it
takes to do the work.
The watt was named after James Watt (17361819), the Scottish engineer who invented
the steam engine.
Another unit of power that is often used for
engine power is the horsepower. Watt
expressed the power of his engines as the
number of horses an engine could replace.
One horsepower is equal to 746 watts.
Who has more power?
P=w/t
P= (100*2)/1
P= 200 W
P= (100*2)/10
P= 20 W
A motor does 5,000 joules of work
in 20 seconds. What is the power of
the motor?
A motor does 5,000 joules of work
in 20 seconds. What is the power of
the motor?
W= 5,000 J
t= 20 s
P= ?
P= 5,000/20
P= 250 W
A machine does 1,500 joules of
work in 30 seconds. What is the
power of this machine?
A machine does 1,500 joules of
work in 30 seconds. What is the
power of this machine?
W= 1,500 J
t= 30 s
P= ?
P= 1,500/30
P= 50 W