Download Section 11.1 The Many Forms of Energy

Mr. Borosky
Physics Section 11.1 Notes
Page 1 of 3
Chapter 11 Energy and Its Conservation
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.
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.
Read intro paragraph p. 285
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
Read Section.
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
Physics Principals and Problems © 2005 Started 2006-2007 School Year
Mr. Borosky
Physics Section 11.1 Notes
Page 2 of 3
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
Read Section.
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 Section.
GRAVITATIONAL POTENTIAL ENERGY
Read Section.
While an object moves up gravity acts against it thus Work is
Negative. When it is moving down the Force and Displacement are in
the same direction and thus the Work is Positive.
Physics Principals and Problems © 2005 Started 2006-2007 School Year
Mr. Borosky
Physics Section 11.1 Notes
Page 3 of 3
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.
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.
Example Problem 1 p. 290
A) PE = mgh
PE = 7.3(9.8)(1.12)
PE = 80.125 Joules
B) PE = mgh
PE = 7.3(9.8)(.51)
PE = 36.485 Joules
C)
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
Read Section.
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
Physics Principals and Problems © 2005 Started 2006-2007 School Year