describe
Work
,
Power
,
and
Energy
in the
context of physics, and quantify each.
I can . . .
Relate
Work
,
Power
,
and
Energy
to real life
situations.
Joules
Newton·meters
foot·pounds
Watts
Horsepower
foot·pounds/second
How do you
WORK ≡ Force · Distance
Work involves
WORK ≡ Force · Distance
UNITS
= Newton · meters
= · m =
kg·m
s
2
kg·m
2
s
2
http://chilipowder.typepad.com/photos/running_photos/img_0983.html
Work = force · distance
= 250 · 0
= 0 Joules
25
0 N
ew
ton
s
Force and Distance have to be
in the
SAME DIRECTION
W ≡ F · d
WORK ≡ Force · Distance
1000 N
6 meters
How much WORK is done by the fork lift?
Force
Distance
ZERO!
W = f · d
Force and Distance have to be in the SAME DIRECTION
WORK ≡ Force · Distance
How much WORK is done by the fork lift?
1000 N
1.5 meters
Force
Distance
Work = force · distance
= 1000 · 1.5
F
o
rc
e
(N
)
Distance (m)
F
o
rc
e
(N
)
Distance (m)
Work on a Spring (J)
1000 N
Force of Friction
= μ
k
·
Normal Force
F
f
= μ
k
·
F
N
μ
k
= .795
F
f
= .795 ·
1000
F
f
=
795 N
6 meters
W = F · D
W = 795 · 6
W = 4,770 J
600 N
5 m
How much WORK does the runner do?
3 m
Work = force · distance
= 600 N · 3m
= 1800 Joules
6.0 meters
51
°
36
0 N
Work =
force
·
distance
=
360
·
cos(51)
·
6.0
http://www.aviationpics.de/prev/crane%203.jpg
2,000 N
15 meters
How much WORK was done in lifting the crate?
Work = 30,000 Joules
http://www.home-gym-direct.com/Images/250x400/Maxicam_Horizontal_Bench_Press_.jpg
How much WORK is done during each press?
0.5 m
Radius = 8.5 m
Tangential velocity = 15 m/s
Mass of car = 1200 kg
Coefficient of friction = .79
Density of air = 1.1 kg/m
3
Age of driver = 18.2 years
Acceleration of gravity = 9.796 m/s
2
How much WORK is done on the
car as it goes around the circle?
Work involves
EFFORT
and
ACCOMPLISHMENT
http://www.andrew-engineering.co.uk/images/Fire_Escape.jpg
Which does
more WORK?
http://www-db.stanford.edu/~widom/photos/temple.jpg
Who did more WORK?
200 lbs
of muscle
UNITS
= Watts
POWER
≡
WORK
Time
Force·Distance
Time
=
Joules
Second
=
=
N·m
s
A
40 Watt
light bulb
DOES
How much
POWER
did the woman exert?
4.0 meters
600 Newtons
8.0 Seconds
How much
WORK
did the woman do?
2,400 Joules
An
average horse
can lift
550 pounds
a distance of
1 foot
in
1 second
.
1 Horsepower ≡ 550 ft·lbs/s
1 ft/s
James Watt
And do it
all day long.
550
550 lbs
a distance of
1 foot
in
1 second.
275 lbs
a distance of
2 feet
in
1 second.
137.5 lbs
a distance of
2 feet
in
0.5 seconds.
Which uses more POWER?
Lifting
:
They all equal 1 Hp !
Force·Distance
Time
http://bp0.blogger.com/_CQd1C2exDNM/RzKYrb9PVhI/AAAAAAAAAA0/x7FYopkEDjM/s1600-h/horse+and+plow+copy.jpg
1 Horsepower ≡ 550 ft·lbs/s
Force·
Distance
Time
POWER =
180 lbs
= Force ·
Velocity
How
fast
could an average
horse pull this plow?
POWER = Force · Velocity
550 = 180 · Velocity
Velocity = 3.1 ft/s
Force·Distance
Time
1 ft = 12 inches 1 inch = 2.54 cm 100 cm = 1 m
2.2 lbs = 1 kg
1 kg = 9.8 N
1 Hp = 550
ft · lbs
s
1 Watt = 1
N · m
s
1 Hp is how many Watts?
Convert 550 ft · lbs to N · m
s s
1 ft = 12 inches 1 inch = 2.54 cm 100 cm = 1 m
2.2 lbs = 1 kg
1 kg = 9.8 N
http://youwon.de/navirechts/wallpapers/Autos/Porsche_index.html
Power = 336 kW
How many Hp?
336,000 W 1 Hp
80 ft
How much time will it take the car to
lift the
3,000 lb crate
if the engine is
115 Hp
?
115 Hp 550 = 63,250
1 Hp
ft·lbs
s
ft·lbs
s
POWER = Force·Distance
Time
63,250 =
3,000 · 80
Time
80 ft
How much time will it take the 3,000 lb
car to climb
the
80 ft
rope if the engine
is
115 Hp
?
115 Hp 550 = 63,250
1 Hp
ft·lbs
s
ft·lbs
s
POWER = Force·Distance
Time
63,250 =
3,000 · 80
Time
How much time will it take the 3,000 lb
car
to climb the
80 ft HILL
if the engine
is
115 Hp
?
80 ft
115 Hp 550 = 63,250
1 Hp
ft·lbs
s
ft·lbs
s
POWER = Force·Distance
Time
63,250 =
3,000 · 80
Time
http://skyscrapercity.com/showthread.php?t=27970
47 stories
1014 stairs
676 ft
fastest time = 6:10 min
(370 seconds)
150 lbs person
POWER = Force·Distance
Time
POWER = 150 lb · 676 ft
370 s
FIELD TRIP
Clifton Bluhm
Calculate YOUR
Horse Power
10.8 ft
ENERGY ≡
WORK
An object that has
100 Joules
of
ENERGY
has the ABILITY to do
100 Joules
of
WORK
2,000 N
15 meters
http://www.aviationpics.de/prev/crane%203.jpg
30,000 Joules
30,000 Joules
How much ENERGY was used to lift the crate?
How much WORK was done in lifting the crate?
If gasoline contains
600,000 Joules of energy per
gallon,
how much gas was used
?
30,000 Joules
1 gal
http://www.maxitmag.com/images/stories/reviews/cellphones/energizer-mobile-phone.jpg
5.0 Amp·hours
18,000 Coulombs
27,000 Joules
5.0 Coulombs ∙ hr
sec
3600 sec
hr
1.5 Joules
Coulomb
Work = Force ∙ Distance
27,000 J = 6.0 N ∙ Distance
Distance = 4,500 m
POWER
≡
Work
Time
POWER is how quickly
WORK is done.
POWER is how quickly
ENERGY is expended.
A
40 Watt
light bulb
DOES
40 Joules
of
WORK
every second.
A
40 Watt
light bulb
USES
POWER ≡
Energy
Time
Energy = Power · Time
= Kilowatt · hour
= 1000 w · 3600 s
1 kWh = 3,600,000 Joules
313 kWh · 3,600,000
Joules
kWh
1,130,000,000 J
1,130,000 kJ
1,130 MJ
1.13 GJ
What is the cost to run this
microwave for 5 hours in a month?
Power = 1200 watts = 1.2 kW
Electric Rate = $ 0.15 / kW·hr
Cost = 1.2 kW · 5 hr · = $ .90
$ 0.15
kW · hr
10 – 100 W light bulbs = 1000 W = 1 kW
6 hours a day for a month = 180 hours
1 kW · 180 hrs = 180 kW·hr
Cost = 180 kW·hr · $ 0.15
kW ·
hr
http://bnikkoco.com/My%20Pictures/new_pa1.jpg
http://www.cnpsaa.org/teenage_bedroom_furniture.html
