CHAPTER 4: ENERGY
Section 1—THE NATURE OF ENERGY
WHAT IS ENERGY?

ENERGY is the ability to
cause change.

When something is able
to change its
environment or itself, it
has energy.
WHAT IS ENERGY?


EXAMPLES—a moving
baseball, a person
walking, the wind blowing
There are different forms
of energy, such as
electrical, chemical, and
thermal.

ELECTRICAL ENERGY—
toaster

CHEMICAL ENERGY—food,
gasoline

THERMAL ENERGY—Sun
AN ENERGY ANALOGY…
ENERGY VS. MONEY
Money comes in many different forms:
 Cash in your wallet
 A bank account—check book
 Traveler’s checks
 Gold or silver coins
Regardless of its form, money is money.
THE SAME IS TRUE FOR ENERGY.

Energy from the Sun
that warms you and
energy from the
food you eat are
only different forms
of the same thing.
KINETIC ENERGY

KINETIC ENERGY is energy in the form of motion. The
amount of kinetic energy depends on 2 quantities—
the mass of the moving object and its velocity.
↑ mass = ↑ KE
↑ velocity = ↑ KE
Kinetic energy = ½ mass x velocity2
 KE (J) = ½ m (kg) x v2 (m2/s2)
 The JOULE is the SI unit of energy.

POTENTIAL ENERGY
Energy does not have to have motion. Even
motionless objects have energy.
 This energy is stored in the object. Therefore,
the object has potential to cause change.
 Stored energy due to position is called
POTENTIAL ENERGY.


EXAMPLES—An apple hanging in a tree has potential
energy (stored energy due to position). If it falls…PE is
converted to KE.
THREE TYPES OF POTENTIAL ENERGY

ELASTIC POTENTIAL ENERGY—is energy stored
by something that can stretch or compress,
such as a rubber band or spring (slinky).

CHEMICAL POTENTIAL ENERGY—is energy
stored in chemical bonds, such as food or
gasoline.
GRAVITATIONAL POTENTIAL ENERGY
Anything that can fall has stored energy called
gravitational potential energy (GPE). (Gravity
caused the apple to fall from the tree.)
 The amount of GPE depends on 3 things:
1. the mass of the object
2. the acceleration due to gravity
3. the height above the ground

GPE (CONTINUED)

MASS is measured in kilograms.

ACCELERATION of gravity on Earth is 9.8 m/s2.

HEIGHT is measured in meters.



GPE = mass x 9.8 m/s2 x height
GPE(J) = m (kg) x 9.8 m/s2 x h (m)
***All energy, no matter which form it is in, can be
measured in joules.
GRAVITATIONAL POTENTIAL ENERGY (GPE)
KINETIC VS. POTENTIAL
CHAPTER 4: ENERGY
Section 2—Conservation of Energy
ENERGY IS MOST NOTICEABLE AS IT
____________ FROM ONE TYPE TO ANOTHER.

Hair Dryer = Electrical
Energy
Thermal Energy
Kinetic Energy
Sound Energy
SOME ENERGY TRANSFORMATIONS ARE
NOT AS OBVIOUS…

Ex. Green plants =
Light energy
Chemical potential
energy
MECHANICAL ENERGY

MECHANICAL ENERGY is the total amount of
Potential and Kenetic energy in a system and
can be expressed by the following equation:

ME= PE + KE
***MECHANICAL ENERGY IS DUE TO THE
___________AND ___________ OF THE OBJECT.

Ex. An apple falling from
a tree…

Gravitational Potential
Energy (GPE) is
converted to Kenetic
energy (KE), but the total
Mechanical energy (ME)
remains constant.
THE LAW OF CONSERVATION OF ENERGY
Energy can change from one form to another
but the total amount of energy never changes.
Another way to say this is that energy is
conserved.
 The law of conservation of energy states that
energy cannot be created or destroyed
 ***The total amount of energy in the universe
remains constant.

POWER PLANT
NUCLEAR POWER PLANT
GEOTHERMAL POWER PLANT
HYDROELECTRIC POWER PLANT