Download Section 11.1

In this chapter you will:
 Learn that energy is a property of an object that can
change the object’s position, motion, or its
environment.
Learn that energy changes from one form to another,
and that the total amount of energy in a closed system
remains constant.
Chapter 11 Sections
 Section 11.1: The Many Forms of Energy
 Section 11.2: Conservation of Energy
Section 11.1 The Many Forms of
Energy
 Objectives
 Use a model to relate work and energy.
 Calculate kinetic energy.
 Determine the gravitational potential
energy of a system.
 Identify how elastic potential energy is
stored.
INTRODUCTION
 Work – transfer of energy by mechanical means.

 Energy – the ability of an object to produce a change in
itself or in its surroundings.

 Conserved Properties – properties that are the same
before and after an interaction. Examples are energy and
momentum.
A MODEL OF THE WORK-ENERGY
THEOREM
 Work – is the product of the force and the object’s displacement. It is equal
to the constant force exerted on an object in the direction of motion times
the object’s displacement. It is the transfer of energy by Mechanical means.
It is denoted by W. It is measured in Joules.
W = Fd
 Energy – the ability of an object to produce a change in itself or in its
surroundings.

 Kinetic Energy – is equal to ½ times the mass of an object times the speed
of the object squared. It is denoted by KE. It is measured in Joules.
KE = ½ mv2
 Work Energy Theorem – states that work is equal to the change in Kinetic
energy.
W = ΔKE
KINETIC ENERGY
 Kinetic Energy – is equal to ½ times the mass of an object
times the speed of the object squared. It is denoted by KE.
It is proportional to the mass and the velocity squared. It is
measured in Joules.
KE = ½ mv2
 Rotational Kinetic Energy – the kinetic energy of an
object, proportional to the object’s moment of Inertia and
the square of its angular velocity.
KERot = ½ Iω2
 Do Practice Problems p. 287 # 1-3
STORED ENERGY
 Read the Section
GRAVITATIONAL POTENTIAL
ENERGY
 While an object moves up gravity acts against it thus Work of
Gravity is Negative. When it is moving down the Force and
Displacement are in the same direction and thus the Work of
Gravity is Positive.
 Gravitational Potential Energy – energy of an object due to position
or state. It is equal to the product of its mass, acceleration due to
gravity, and the distance from the reference level. It is measured in
Joules. It is denoted by PE.
PE = mgh
(Potential Energy = mass * gravity * height)
 Reference Level – location at which potential energy is chosen to be
zero.
GRAVITATIONAL POTENTIAL
ENERGY
 Note: PE = mgh is only valid if the gravitational
force and acceleration are constant.
 The sum of the Kinetic Energy and Potential
Energy is constant at all times because no work
is done on the system by any external forces.
GRAVITATIONAL POTENTIAL
ENERGY
 Example Problem 1 p. 290
A) PE = mgh
PE = 7.3(9.8)(1.12)
PE = 80.125 Joules
C)
B) PE = mgh
PE = 7.3(9.8)(.51)
PE = 36.485 Joules
W = ΔKE = ΔPE
W = mghF – mghI
PE = 7.3(9.8)(1.12) – 7.3(9.8)(.61)
W = 80.125 – 43.6394
W = 36.4856 J (This is the work you do and SO)
Work by gravity is opposite and thus -36.485 Joules
 Do Practice Problems p. 291 # 4-8
ELASTIC POTENTIAL ENERGY
 Elastic Potential Energy – the potential energy that may
be stored in an object, such as a rubber band, as a result of
its change in shape.
 Albert Einstein – said that Mass by itself is energy. This
energy is called the Rest energy and thus the famous
equation E = mc2.
 Rest Energy – is equal to the object’s mass times the speed
of light squared. E = mc2.
 Do 11.1 Section Review p. 292 # 9-14