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November 3rd, 2015
• Work, Power and Energy Unit Notes (#45)
• Independent Practice Online
Work, Power and
Energy
Unit Notes
2015
What is Work?
• The product of force and distance
Work = Force x Distance
What is the unit for work?
The Joule is the standard unit of work.
1 Joule = 1 Newton x 1 meter
Work Requires Motion
• IF there is NO movement, NO work is done.
Work Depends on Direction
• Any part of a force that does not act in the
direction of motion does no work on an object.
• Video
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In order for a force to qualify as having done
work on an object, there must be movement and
the force must cause the movement.
Read the following statements and determine
whether or not they represent examples of
work. Write Yes or No.
1. A teacher applies a force to a wall and becomes
exhausted. NO, the object does not move in the direction of the forc
2. A book falls off a table and free falls to the
ground. YES! Gravity is the force pulling the book towards the ground.
3. A rocket accelerates through space. YES!
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What is Power?
• Power is the quantity that measures work in relation to
time. In other words it is the rate at which work is
done.
Power = Work ÷ Time
The standard unit for Power is the Watt.
1 watt = 1 Joule/1 Second
One Horsepower = 750 watts
Real-World Connection
• Running up the stairs takes less time than walking up
the stairs. Doing the same amount of work each time,
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how does this affect
the power?
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Energy & Conservation of
Energy
The Ability To Do Work
What Is Energy?
 Energy is a property of objects which can be
transferred to other objects or converted
into different forms, but cannot be created
or destroyed.
 Our measuring unit for energy is the
JOULE(J)
Did you Know??
Energy comes in many forms. All forms of energy are
convertible to other kinds of energy and obey the law
of conservation of energy, which says that energy
can be neither created nor destroyed; however, it can
be changed from one form to another.
Energy
 The two forms of energy we will concentrate on are:
 Potential Energy
 This is energy that is stored, waiting to do work. Think of a
battery or an acrobat poised to drop onto a see-saw.
 Video
 Kinetic Energy
 This is the energy of action! Objects turning, flying, dropping,
shooting!
 Video
Calculating Potential Energy
 Potential Energy
PE=mgh
PE = mass x gravity x height
Gravity = 9.8 m/s2
*All Energy is measured in Joules.
1. A 35 kg mass is lifted to a height of 4
meters. What is the potential energy of the
mass?
PE = mgh
M = 35 kg
H = 4 meters
G = 9.8 m/s2
PE = (35 kg)(9.8m/s2) (4 m) = 1372 Joules
2. What is the potential energy of a 61.2
kilogram person standing on the roof of a
building that is 2.5o meters tall?
PE = mgh
M = 61.2 kg
g = 9.8 m/s2
h = 2.50 meters
PE = (61.2 kg) (9.8 m/s2) (2.50 meters) = 1499.4 J
3. Johnny, who has a mass of 80 kilograms, is
standing at the top of a flight of stairs that is 35 meters
tall. How much potential energy does Johnny have?
PE = mgh
M = 80 kg
g = 9.8 m/s2
H = 35 meters
PE = (80kg) (9.8m/s2) (35 m) = 27440 J
Kinetic Energy
 Kinetic energy is the energy of movement. It also
depends on mass, but it depends even more on velocity.
 Kinetic Energy
1
2
KE= mv
2
KE =
1
mass
2
x velocity2
Energy is always measured in Joules
What is the kinetic energy of a 56 kg mass
moving with a velocity of 3 m/s?
 1.
KE = ½ mv2
M = 56 kg
V = 3 m/s
KE = ½ (56 kg) (3m/s)2= 252 J
 2. A ball has a mass of 20 grams and is thrown with
a velocity of 12 m/s. What is the kinetic energy of the
ball?
KE = ½ mv2
M = 20 g
V= 12 m/s
KE = ½ (20 g) (12 m/s)2= 1440 J
3. Calculate the kinetic energy of a 45 gram golf ball
traveling at 20 m/s.
KE = ½ mv2
M = 45 kg
V = 20 m/s
KE = ½ (45 kg) (20 m/s)2= 9000 J
 All the energy in the universe is…
 The total amount of all the energy in the universe is…
 A. Slightly increasing
 B. Slightly decreasing
 C. Always the Same
 D. Always Zero
 Temperature is a measure of a group of molecule’s




_________.
A. Kinetic Energy
B. Potential Energy
C. Sum of Kinetic and Potential Energy
D. None of the Above
 Kinetic Energy is ___________.
 A. The energy of your dancing motions.
 B. The energy of molecule’s motion: bending,
stretching, twisting, and flying through space.
 C. The energy of a baseball’s motion right after it’s
thrown.
 D. All of the above.
 Energy from food________.
 A. Keeps you warm
 B. Is stored for later
 C. Is used to keep your heart beating.
 D. All of the above.
 If a piece of meter at 70 degrees touches a piece of




metal at 40 degrees, _______.
A. Energy will flow from the hotter metal to the
cooler metal.
B. Cold will flow from the cooler metal to the hotter
metal.
C. Nothing will happen.
D. It’s impossible to tell.
Energy Sources
 Energy sources can be divided into two groups:
 Renewable: An energy source that can be easily replenished.
 Nonrenewable: An energy source that cannot be easily
replenished.
 There are 5 main renewable energy sources:
 Solar Energy from the sun, which can be turned into electricity
and heat.
 Wind energy
 Geothermal energy from heat inside the earth
 Biomass from plants, which includes firewood from trees,
ethanol from corn and biodiesel from vegetable oil.
 Hydropower from hydroelectric turbines.
How is wind energy turned
into electricity?
Create a flow chart on your
whiteboard
Group Discussion
What is “clean energy”?
Why is wind energy
considered “clean energy”?
Draw a wind turbine
on your whiteboard
Wind Turbine Project
 https://youtu.be/tsZITSeQFR0