POWER
What is the work done in climbing a flight of
stairs of height h?
W=F•d
d
What is the work done in climbing a flight of
stairs of height h?
W=F•d
POWER
Power = Work / Time
POWER IS:
Do you get more tired
when you run or when
you walk up the stairs?
• the rate at which work is done
• how fast work is done
• how much work you can do per second
What is the difference?
h
TIME
POWER
POWER
Metric system units for Power are:
Electric Power = Current × Voltage
Watts (W)
What are the units for Power?
1 Watt = 1 Joule per second
1 W = 1 J/s
1
POWER
Other units for Power:
W
Electrical Power is sold in kilowatt/hours (kWh):
P
1 kW = 3,600,000 J/hr
t
Cars and Machines are rated in Horsepower (hp)
1 hp = 746 W (a very strong horse! )
MEASURED IN
JOULES (J)
MEASURED IN
WATTS (W)
MEASURED IN
SECONDS (s)
1 W = 1 J/s
Electric Power = Current × Voltage
POWER
What is the work done in climbing a flight of
stairs of height h?
W=F•d
Watt Demonstration:
Lift a 1-N mass a distance of 1
meter, and you have done 1 Joule
of Work.
Do this once each second, and
your power output is 1 Watt.
What is the work done in climbing a flight of
stairs of height h?
W=F•d
d
POWER
Power = Work / Time
POWER IS:
Do you get more tired
when you run or when
you walk up the stairs?
• the rate at which work is done
• how fast work is being done
• how much work you can do per second
What is the difference?
h
TIME
2
Example:
• next…
What is the power output of a 100 N
person who runs up a 10 m high flight of
stairs in 2.5 s?
W = Fd
= (100 N)x(10 m)
= 10,000 J
P=W/t
= (10,000 J) / (2.5 s)
h
= 4000 W
Power, Energy, Work …
all together now.
THE RATE OF DOING WORK OR
CONVERTING ENERGY.
Power = Work / Time
Power = Energy / Time
UNIT- WATT = JOULE PER SECOND
3