Download Work, YA!!!!!! Finally something easy

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As Ice Cube once said ‘Work is ‘bout getting
paid yo!”
Luckily for us that’s not what work is, work is
how much force and distance is needed to
move or do something.
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W=f x d where f is force (N) and d is distance
in (M), so our units for work are Nm but
because people like to make things confusing
for you, a Nm is also a joule (J).
Ohhh Pretty!!!!
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James Prescott Joule (24
December 1818 – 11 October
1889) was an
English physicist and brewer
(maker of beer – yum yum).
Born in Salford, Lancashire (North
West England).
Joule studied the nature of heat,
and discovered its relationship to
mechanical work - i.e ENERGY.
James Joule
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How much work does Esther do if she lifts a
75N load of rice into the back of her
vehicle1.4 m off the ground?
W=fxd
W = 75 x 1.4
W= 105 Nm or 105J
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Sometimes we waste our energy doing work
when we’re not parallel to the object we wish
to work on. Make sense?
EX Pushing a box at an angle means the box
moves to the direction wanted but some work
is wasted up or down, as our desired
outcome is to move the box left to right.
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We use this new formula:
W= F x D x cos(x)
Where when we break it down like vectors we
use the cosine function to find our horizontal
work.
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Mr. Willard got stuck in mud. He’s pushing on
his vehicle at a 27 degree angle with 1000N
of force. If I get my car free and it moves 1.5
meters, how much work did I put into the
situation?
W = f x d x cos(x)
W = 1000 x 1.5 x cos(27)
W= 1336.5 Nm or J
Energy is: the ability of an object to
produce a change in itself or the world
around it.
 Law of Conservation of Energy: Energy
isn’t created or destroyed it simply
changes forms.
 This means Einitial=Efinal
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Kinetic Energy: Is the energy of
movement, so running requires kinetic
energy, a ball rolling has kinetic
energy.
 We are able to calculate this energy
using a formula:
Ke=1/2mv2
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What is the kinetic energy of a cheetah who
has a mass of 104 kg running at 34 m/s?
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Ke=1/2mv2
Ke = ½ x 104 x 342
Ke = 60112 J
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This stuff is easy, right? 
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Work is also defined as the change in kinetic
energy. How so you ask? Good question.
Because work requires velocity or movement,
whenever something moves or changes it
requires work. Because movement is kinetic
energy this should all make sense.
So work:
W = ∆KE (because it’s a change its final –
initial)
W = KEf-KEi
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How much work would be required to slow down
a bear charging at you if the mass was 109kg
and he was running at 17 m/s?
W = (1/2mv2f) - (1/2mv2i)
W= .5 x 109 kg x 0 m/s - .5 x 109 kg x 17m/s2
W= 15750.5 J or Nm
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You’ll see again it’s possible to graph the
work we do. Simply stated force goes on the y
axis and distance on the x.
On the next slide I’ll show how easy it is.
Compare the Formula for Area and Work
A=LxW
W=Fxd
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10m
Length
(m)
10 N
W=Fxd
A=LxW
Force
(N)
A = 10m x
4m
W = 40 N·m
W = 40 J
A = 40m2
Width
(m)
W = 10N x 4m
4m
Distance
(m)
4m
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Gravitational Potential Energy - ughhhh, writing
it out so long! Just use GPE or PE.
GPE: is energy that we have due to the earth’s
gravitational pull, our mass and a height.
This should make sense because by definition of
work, energy is
required to move
things.
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Ep = mgh
WHERE:
Ep = gravitational potential energy (J)
m = mass (kg)
g = acceleration due to gravity (9.80m/s2)
h = height (m)
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A picture with a mass of 3.8kg hangs on a wall
2.1m above the ground. What is the gravitational
potential energy of the picture relative to the floor?
Ep = mgh
m = 3.8kg
g = 9.80m/s2
h = 2.1m
Ep = (3.8kg)(9.80m/s2)(2.1m)
Ep = 78.2J
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Temperature: is a measurement of the average kinetic
energy of the molecules in an object or system and can be
measured with a thermometer. It is a means of
determining the internal energy contained within the
system.
Thermal Energy: A measure of internal motion of an
objects particles. (always tries to equalize from hot to
cold)
Specific heat capacity: the amount of heat it takes to raise
the temperature of a 1g substance by one degree Celsius
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Specific heat capacity is the amount of heat
energy required to raise the temperature of a
substance per unit of mass.
Heat Capacity Symbol: ‘C’ is the amount of
heat in joules required to raise 1 gram or
kg of a substance 1 degree celsius.
Water’s specific heat capacity is 4.18 J/g °C
or 4180 J/kg °C
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C = Specific Heat Capacity (J/goC)
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Q = Amount of Heat (J)
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m = Specific Mass (g)
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∆T = Change in temperature (oC)
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Suppose you want to make some soup, and
you need to heat 500g of water from 10.2oC
to 98.7oC. Calculate the amount of heat
required to do this.
m = 500g
c = 4.19 J/goC (specific heat capacity of
water)
T = 98.7 – 10.2 = 88.5oC
Q=?
Q = mc∆T
Q = (500g)(4.19 J/goC)(88.5oC)
Q = 185407 J
Q = 1.85x105 J
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Suppose you use a 0.40kg stainless steel pot
to warm 2.0kg of water from 12oC to 38oC.
Calculate the heat required to warm the water
and the pot. The specific heat capacity of the
stainless steel is 0.510J/goC.
m = 0.4kg = 400g (pot)
m = 2.0kg = 2000g (water)
T = 38oC - 12oC = 26oC
C = 0.510 J/goC (pot)
C = 4.18 J/goC (water)
Q = ? (pot)
Q = ? (water)
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Q = mc∆T
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Q = (400g)(0.510J/goC)(26oC)
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Q = 5304J
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Q = mc∆T
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Q = (2000g)(4.19J/goC)(26oC)
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Q = 217880J
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Qtotal = 5304J + 217880J = 223184J
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Q = 2.2x105J
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Absolute zero - the coldest temperature
possible ever, -273.5 degrees Celsius
Three types of temp measure: Kelvin (K),
Celsius(C) and Fahrenheit(F).
Conversions:
◦ K to C: K – 273
◦ C to K: C + 273
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Conduction: Contact between particles. IE
candle and a flame
Convection: A mixture of heat because of a
flow. IE boiling water hot and cold continually
mix.
Radiation: The transfer of energy through
electromagnetic waves.