Bryant Noriega
11 Energy and Its Conservation
BIGIDEA
Write the Big Idea for this chapter.
Within a closed, isolated system, energy can change form but the total energy is constant
Use the “What I Know” column to list the things you know about the Big Idea. Then list the
questions you have about the Big Idea in the “What I Want to Find Out” column. As you read the
chapter, fill in the “What I Learned” column.
W
What I Want to Find Out
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K
What I Know
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L
What I Learned
11 Energy and Its Conservation
1 The Many Forms of Energy
MAINIDEA
Write the Main Idea for this section.
kinetic energy is due to an object's motion, and potential energy
is energy due to the interactions of two or more objects
REVIEW VOCABULARY
Recall and write the definition of the Review Vocabulary term.
system
system the object or objects of interest that can interact with
each other and with the outside world
NEW VOCABULARY
rotational kinetic energy
potential energy
Use your book to fill in the term that matches each definition.
energy due to rotational motion
energy stored due to interactions between objects in a system
gravitational potential energy
stored energy due to the gravitational force between objects
reference angle
elastic potential energy
Student Edition, pp. 292–293
stored energy due to an object’s change in shape
the sum of the kinetic energy and potential energy of the particles in a
system
Identify two ways work can change the kinetic energy of an object.
work can be done by a force to increase velocity. It can also
cause friction to oppose the force and decrease velocity
Science Notebook • Energy and Its Conservation
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Copyright © McGraw-Hill Education. Permission is granted to reproduce for classroom use.
thermal energy
position where GPE is defined to be zero
1 The Many Forms of Energy (continued)
Student Edition, pp. 292–297
Differentiate When should Wg = mgh have a negative sign?
when the objects displacement is upward and gravitational force
is downward
Describe the work done by gravity as the orange rises from
the juggler’s hand.
GET IT?
while the orange moves upward gravity does negative work, on
the way back down, gravity does positive work increasing speed and kinetic
Explain why it is important to specify a reference level before you
calculate the gravitational potential energy of an object.
It is important to determine a reference level before calculating
the GPE because you will need to know where the stored energy
will equal to zero
Copyright © McGraw-Hill Education. Permission is granted to reproduce for classroom use.
Use with Example Problem 1.
Use this column for
scratch work and
sketches.
TRY IT !
Problem
GRAVITATIONAL POTENTIAL ENERGY You lift a 6.5-kg backpack from a
chair that is 0.47 m above the floor (hc) to a desk that is 0.75 m above the
floor (hd)
a. When the backpack is on the desk, what is the backpack-Earth
system’s gravitational potential energy relative to the floor (GPE1)?
b. When the backpack is on the desk, what is the backpack-Earth
system’s gravitational potential energy relative to the chair (GPE2)?
c. How much work was done by gravity as you lifted the backpack
from the chair to the desk?
1. ANALYZE AND SKETCH THE PROBLEM
KNOWNS
UNKNOWNS
m = 6.5 kg
g = 9.8 n/ Kg
GPE 1 = ? w
hd = 0.75 m
hc = 0.47 m
GPE 2 = ?
Science Notebook • Energy and Its Conservation
165
=?
1 The Many Forms of Energy (continued)
Student Edition, pp. 297–300
TRY IT ! (continued)
2. SOLVE FOR THE UNKNOWNS
a. Set the floor as the reference level. Determine GPE1.
b. Set the chair as the reference level. Determine GPE2.
First determine the height of the desk relative to the chair.
Next use this difference in height to determine GPE2.
c. Calculate work by multiplying the weight of the backpack times
the distance it was lifted. The direction of weight is opposite
that of h.
• Explain why the two values of GPE are reasonable.
GET IT?
Define the term elastic potential energy.
stored energy due to an objects change in shape
Decide A student states that thermal energy is the sum of an object’s
kinetic energy and potential energy. What is wrong with the statement?
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3. EVALUATE THE ANSWER
Thermal energy the sum of the kinetic energy and potential energy
of the particles in a system
Science Notebook • Energy and Its Conservation
166
1 The Many Forms of Energy (continued)
SUMMARIZE
How does the MAINIDEA for this section relate to the chapter’s BIGIDEA?
REVIEW IT !
11. MAINIDEA How can you apply the work-energy theorem to lifting a bowling ball
from a storage rack to your shoulder?
the balls kinetic energy while resting on the rock is zero which means the work done
on the ball would be zero
12. Elastic Potential Energy You get a spring-loaded jumping toy ready by compressing
the spring. The toy then flies straight up. Draw bar graphs that describe the forms of
energy present in the following instances. Assume the system includes the spring toy
and Earth.
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a. The toy is pushed down, thereby
compressing the spring.
b. The spring expands and the toy
jumps.
c. The toy reaches the top of its flight.
Science Notebook • Energy and Its Conservation
167
1 The Many Forms of Energy (continued)
12. Potential Energy A 25.0-kg shell is shot from a cannon at Earth’s surface. The reference
level is Earth’s surface.
a. What is the shell-Earth system’s gravitational potential energy when the shell’s
height is 425 m?
= (25)(9.8)(225) = 104125 J
b. What is the change in the system’s potential energy when the shell falls to a height
of 225 m?
13. Potential Energy A 90.0 kg rock climber climbs 45.0 m upward, then descends 85.0 m.
The initial height is the reference level. Find the potential energy of the climber-Earth
system at the top and at the bottom. Draw bar graphs for both situations.
the angular momentum would also double because it relates to velocity. the rotational
KE would be 4 times as much because it relates to the angular velocity squared
Science Notebook • Energy and Its Conservation
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14. Rotational Kinetic Energy On a playground, some children push a merry-go-round so
that it turns twice as fast as it did before they pushed it. What are the relative changes
in angular momentum and rotational kinetic energy of the merry-go-round?
1 The Many Forms of Energy (continued)
15. Critical Thinking Karl uses an air hose to exert a constant horizontal force on a puck,
which is on a frictionless air table. The force is constant as the puck moves a fixed
distance.
a. Explain what happens in terms of work and energy. Draw bar graphs.
he exerted a constant force over a
certain distance which changed the work
b.
Suppose Karl uses a different puck with half the first one’s mass. All other
conditions remain the same. How should the kinetic energy and work done differ
from those in the first situation?
it would still receive the same work and has the same change in energy. but it will
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move faster
c.
Describe what happened in parts a and b in terms of impulse and momentum.
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