Transcript Chapter 11: Motion

C HAPTER 15:
E NERGY
S ECTION 15–1:
E NERGY AND I TS F ORMS
O BJECTIVES

Describe the relationship between work and energy.

Relate kinetic energy to mass and speed and calculate
these quantities.

Analyze how potential energy is related to an object’s
position and give examples of gravitational and elastic
potential energy.

Solve equations that relate an object’s gravitational
potential energy to its mass and height.

Give examples of the major forms of energy and explain
how each is produced.
E NERGY
AND
W ORK

Remember from chapter 14 that work is done when a
force moves an object through a distance.

Energy is the ability to do work. It is transferred by a
force moving an object through a distance.

Work and energy are closely related. Work is a transfer
of energy. Both work and energy are measured in
joules (J), and a joule is a newton-meter.
K INETIC E NERGY

Many forms of energy can be classified into two general
types: kinetic energy and potential energy.

The energy of motion is called kinetic energy. The
Greek word kinetos means “moving.”

The kinetic energy of any moving object depends upon
its mass and speed.

To calculate the kinetic energy of an object in joules,
multiply the object’s mass in kilograms, the square of its
velocity (speed) in meters per second, and ½.
KE = ½mv2
S AMPLE P ROBLEM – K INETIC E NERGY

A 0.10 kilogram bird is flying at a constant speed of 8.0
m/s. What is the bird’s kinetic energy?

Given:
Mass: 0.10 kg
Speed: 8.0 m/s

Solve:
KE = ½mv2
KE = ½(0.10 kg)(8.0 m/s)2
KE = ½(0.10 kg)(64 m2/s2)
KE = 3.2 kgm2/s2
KE = 3.2 J
P OTENTIAL E NERGY

Potential energy is the energy that is stored as a result
of position or shape.

Pulling a string tightly before plucking it and holding a
book in the air are examples of objects with potential
energy.

There are two forms of potential energy: gravitational
potential energy and elastic potential energy.
G RAVITATIONAL P OTENTIAL E NERGY

Potential energy that depends upon an object’s height
is called gravitational potential energy. This type of
potential energy increases when an object is raised to a
higher level.

An object’s gravitational potential energy depends on
its mass, its height, and the acceleration due to gravity.
Remember that on Earth, g is always 9.8 m/s2.
GPE = mgh
S AMPLE P ROBLEM – P OTENTIAL E NERGY

Suppose a diver is at the top of a 10.0-meter-high diving
platform has a mass of 50.0 kilograms. What is her
gravitational potential energy?

Given:
Height: 10.0 m
Mass: 50.0 kg
Gravity: 9.8 m/s2

Solve:
GPE = mgh
GPE = (50.0 kg)(9.8 m/s2)(10.0 m)
GPE = 4900 kgm2/s2
GPE = 4900 J
E LASTIC P OTENTIAL E NERGY

The potential energy of an object
that is stretched or compressed is
known as elastic potential energy.

Something is said to be elastic of it
springs back to its original shape
after it is stretched or compressed.

When you drop a slice of bread on
the ground, it may barely bounce.
This is because it is not very elastic.
When you drop a golf ball, it
bounces almost back to where it
was dropped from.
F ORMS
OF
E NERGY

All energy can be considered to be kinetic energy,
potential energy, or the energy in fields such as those
produced by electromagnetic waves.

The major forms of energy are mechanical energy,
thermal energy, chemical energy, electrical energy,
electromagnetic energy, and nuclear energy.
M ECHANICAL E NERGY

The energy associated with motion and position of
everyday objects is mechanical energy.

Mechanical energy is not limited to machines.
Mechanical energy is the sum of an object’s potential
energy and kinetic energy.

Speeding trains, bouncing balls, and sprinting athletes
all have mechanical energy.
T HERMAL E NERGY

Almost all of the matter around you contains atoms.
These particles are always in random motion and thus
have kinetic energy.

The total potential and kinetic energy of all the
microscopic particles in an object make up its thermal
energy.

When an object’s atoms move faster, its thermal energy
increases and the object becomes warmer. If they get
hot enough, they may emit visible light.
C HEMICAL E NERGY

Chemical energy is the energy stored
in chemical bonds. When bonds are
broken, the released energy can do
work.

All chemical compounds, including
fuels like coal and gasoline, store
energy.

Burning wood at a campfire is
considered chemical energy because
the chemical bonds in the wood are
being broken. This provides thermal
energy to roast marshmallows!
E LECTRICAL E NERGY

Electrical energy is the
energy associated with
electric charges.

Batteries convert
chemical energy into
electrical energy.

Lightning bolts are
produced by electrical
energy.
E LECTROMAGNETIC E NERGY

Electromagnetic energy is a
form of energy that travels
through space in the form
of waves.

X-rays and visible light are
examples of
electromagnetic energy.

Because they can travel
long distances through air
and space, they are often
used in communication.
N UCLEAR E NERGY

The nucleus of an atom is held
together by strong and weak
nuclear forces, which can store
an enormous amount of
potential energy.

The energy stored in atomic
nuclei is known as nuclear
energy.

Nuclear fission and fusion are
processes that create and use
nuclear energy.
V OCABULARY

Energy

Thermal energy

Kinetic energy

Chemical energy

Potential energy

Electrical energy

Gravitational potential
energy

Electromagnetic energy

Nuclear energy

Elastic potential energy

Mechanical energy