Transcript Chapter 5

Chapter 9
Energy and Energy Resources
Terms to Learn
• Energy: the ability to do work.
• Kinetic Energy: the energy of motion(KE)
depends on speed and mass
• Potential Energy: the energy of position or
shape.(PE)
ENERGY
• Energy is the ability
to do work; work is
the transfer of
energy.
• Both energy and
work are expressed
in Joules (J).
ENERGY
• The tennis player is
doing work on her
racket because she has
energy
• When she does work
on the racket, the
racket gains the ability
to do work on the ball.
ENERGY
• Energy is transferred from the tennis
player to the racket.
• When the racket does work on the ball,
the ball gains the ability to do work on
something else. Energy is transferred
from the racket to the ball.
Forms of Energy
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Thermal energy
Chemical energy
Electrical energy
Sound energy
Light energy
Nuclear energy
FORMS OF ENERGY
1. Thermal energy – the total energy of the
particles that make up an object.
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The higher the temperature, the faster
particles move and the more K.E. they have
Thermal energy also depends on the number
of particles there are in a substance.
See Figure 5 on p. 244
FORMS OF ENERGY
2. Chemical energy – the energy of a
compound that changes as its atoms are
rearranged to form new compounds.
Chemical energy is a form of potential
energy.
Electrical Energy
• Is the energy of
moving electrons
Both kinetic and
potential energy
Sound Energy
• Is caused by an
object’s vibrations
• It is a form of
potential and kinetic
energy
Light Energy
• Is produced by the
vibrations of
electrically charged
particles
• Kinetic energy
Nuclear Energy
• The energy associated
with changes in the
nucleus of an atom
Nuclear power plants
use uranium, a
radioactive element,
to create electricity.
• Potential Energy
Kinetic Energy
• Kinetic energy=mv2
2
m=mass (kg)
v=velocity (m/s)
KE=Joules
As the roller coaster
descends its velocity
increases causing the
roller coaster to gain
kinetic energy.
TYPES OF ENERGY
• Kinetic Energy (K.E.)
– Depends on:
• Speed and
• Mass
– Speed has more of an effect on Kinetic
Energy than mass because speed is
squared in the equation.
POTENTIAL ENERGY
• Also known as P.E. or
G.P.E.
• Energy of position or
shape
• Gravitational potential
energy depends on:
– Weight and
– Height (distance above
Earth’s surface)
POTENTIAL ENERGY
• The stored potential
energy of the bow
and string allows
them to do work on
the arrow when the
string is released
POTENTIAL ENERGY
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Equation for GPE:
GPE = weight ● height
or
GPE = mass ● g ● height
Weight = mass ● g
Potential Energy
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GPE is measured in Joules (J)
mass is measured in kg
height is measured in meters (m)
g is acceleration due to gravity and is a
constant number- 9.8 m/s2
Energy Partners
Terms to Learn
• Mechanical Energy: is the total energy of
motion and position of an object. It can be
all potential energy, all kinetic energy, or
some of both.
• Mechanical energy = potential energy + kinetic energy
• ME=PE+KE
Mechanical Energy
When potential energy increases (or
decreases), kinetic energy has to decrease
(or increase) in order for mechanical energy
to remain constant.
Chapter 9
Conservation of Energy
Energy Is Conserved Within a Closed System
• A closed system is a group of objects that transfer
energy only to each other.
• The Law of Conservation of Energy states that
energy cannot be created or destroyed.
• Energy can be converted from one form to another.
But all of the different forms of energy in a system
always add up to the same total amount of energy.
No Conversion Without Thermal
Energy
• During energy conversions some of the
original energy is always converted into
thermal energy
• This is due to friction
• This energy is not always useful