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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 therefore:
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). Named after
James. There’s a reason for that…
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How much work does Frank do if he lifts a
75N load of rice into the back of his truck 1.4
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 yes 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.
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. Caddy got stuck in mud. He’s pushing on his
vehicle at a 27 degree angle with 1000N of force.
If I get my truck free and it moves 1.5 meters,
how much work is done?
W = f x d x cos(x)
W = 1000 x 1.5 x cos(27)
W= 1336.5 Nm or J
Work and force aren’t the same thing if you drew
a triangle just so you know because I made the
same mistake!
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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 Ebefore=Eafter
You might think WHOA!!! Not true. WRONG it
is. It doesn’t mean all energy is useful energy
but its still there.
Show that thing from smartboard you have
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Kinetic Energy: Is the energy of movement, so
running requires kinetic energy, a ball rolling
has kinetic energy. Get it? Good.
We are able to calculate this energy using a
fun 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?
Ke=1/2mv2
.5 x 104 x 342
= 60112J
This stuff isn’t to hard on it’s own. Shortly I’ll
take it hard because I’m THAT guy.
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Although this isn’t required by BC to get
learned it makes sense so I’m teaching it.
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)
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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?
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W = (1/2mv2f) - (1/2mv2i)
W= .5x109x0 - .5x109x172
W= 15750.5J or Nm
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Lets try some in our text on 261
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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. It’s
easy as 3.14
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
A = 40m2
Width
(m)
W = 10N x
4m
4m
W Distance
= 40 J
(m)
4m
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So basically it’s just like when we found
displacement and such from our vt graphs.
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GPE: (writing it out so long!) 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. Use example
Ep = mgh
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
Ep = (3.8kg)(9.80m/s2)(2.1m)
m = 3.8kg
g = 9.80m/s2
Ep = 78.2J
h = 2.1m
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A 65.0 kg pole vaulter runs along a track at a
speed of 7.9 m/s, which gives him kinetic
energy of 2.03 x 103 J. Using the pole to
change the direction of his motion, he lifts
himself up a height of 3.68 m in the air—an
Olympic-level performance.
(a) How much potential energy does the
vaulter gain at the top of his vault?
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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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The property of water that gives it the ability
to moderate the temperature of both the
environment and living bodies is its HEAT
CAPACITY
Absorption of heat is dependent in the
specific heat capacity of the surface
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Which area of Alberta has air with high
specific heat capacities?
◦ Those near large bodies of water
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How can you tell?
◦ Because of the smaller differences between
day time and night time temperatures
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What about Calgary? High or low specific heat
capacities?
LOW – Temperature is quite dry, therefore
they have large temperature swings between
day and night
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C = Specific Heat Capacity (J/goC)
◦ Table on pg 318
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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
T = 98.7 – 10.2 = 88.5oC
Q=?
Q = mc∆T
Q = (500g)(4.19J/goC)(88.5oC)
Q = 185407J
Q = 1.85x105J
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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 = 0.510J/goC (pot)
C = 4.18J/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 rod
in 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.
Examples now on 319.