Download What is Energy?

What is
Energy?

What is the relationship between energy and work?

Compare kinetic and potential energy

What are the different types of energy?
What is energy?

Energy is the ability to do work.

Great, but what is work?

Work is done when a force (caused by energy)
causes an object to move.

Work = Force x distance
Energy / Work

Energy is needed to push a box across the
floor. The box moving across the floor is
an example of work.

Energy is needed to hit a home run. The
ball flying over the fence is an example of
work.
Two Basic Types of Energy

Potential Energy = the energy of an object
due to its position, shape, or condition

Kinetic Energy = the energy of an object
due to the object’s motion
Potential Energy

Not all energy has to do with motion.

Potential Energy is the energy an object
has because of its position, shape, or
condition.

Objects with potential energy have the
potential, or ability, to do work.
Potential Energy Preview

We will learn about three kinds of
Potential Energy
1.
Elastic Potential Energy
Chemical Potential Energy
Gravitational Potential Energy
2.
3.
Elastic Potential Energy

The bow has energy because work
has been done to change its shape.

The energy of that work is turned into
potential energy.

When the arrow is released the
potential energy of the bow and string
will be transferred to the arrow,
sending it flying through the air.
Elastic Potential Energy

Compressed, or squished, springs
also have potential energy.

A spring has energy because work
has been done to change its shape.

Just like the bow, the energy of that
work is turned into potential energy.
Elastic Potential Energy

What about rubber
bands and other
things that stretch?

Elastic Potential
Energy
How do we “release” the potential
energy stored in springs?
Chemical Energy
Chemical Energy is the potential energy
stored in substances.
 Calories = the chemical energy of food
 Batteries also have chemical energy
 It all depends upon the position and
arrangement of the atoms in a compound.

Chemical Potential Energy

A battery has potential energy
due to its condition.

Potential Energy is stored in
the chemicals within the
battery.

A fully charged battery has the
potential to do work.
Chemical Potential Energy

Chemical Potential
Energy can be found
in food.

Calories!
Chemical Energy (cont’d)
 Which
type of
food has the
highest chemical
potential energy
(calories)?
Gravitational Potential Energy

When someone pushes you on a
swing, you and the swing gain
potential energy because work has
been done to change your position.

You will have the most potential
energy at the top, right before you
begin your arc downward.

Think about swinging. When will
you have the most kinetic energy?
Gravitational Potential Energy




When you lift an object, you do work on it.
You use a force that is against the force of
gravity.
When you do this you transfer energy to the
object and give the object Gravitational Potential
Energy.
The amount of Gravitational Potential Energy an
object has depends on the objects weight and
height above the ground.
Gravitational Potential Energy

Books on a shelf have
Gravitational Potential
Energy.

Which books have the
most Gravitational
Potential Energy?
Why?
Gravitational Potential Energy

A man and his cell phone are on
a ledge outside a very tall
building.

Which object (the man or his
cell phone) has the most
Gravitational Potential Energy?
Why?
How do we calculate
Gravitational Potential Energy?

GPE = Weight x Height

Measure Weight in Newtons (N)

Measure Height in meters (m)

The unit for Gravitational Potential Energy
= Newton meters (Nm) or Joules (J)
Calculate the Gravitational
Potential Energy

GPE = Weight x Height

Book #1 weighs 25 N on a shelf that
is 2 meters off of the ground.

Book #2 weighs 25 N and is on a
shelf only 1 meter off of the ground.

Which book has the most GPE?
Calculate the Gravitational
Potential Energy

GPE = Weight x Height

Man weighs 300 N on a ledge that
is 200 meters off of the ground.

Cell Phone weighs 15 N and is on
the same ledge.

Which object has the most GPE?
Practice Calculating GPE

GPE = Weight x Height

Tools: Metric tape measure, spring scale
(be sure to use the Newton scale),
calculator

Units! Units! Units! ~ The units for GPE
are Newton meters (Nm) or Joules (J)
Potential Energy Review

We learned about three kinds of Potential
Energy
1. Elastic
Potential Energy
2. Chemical Potential Energy
3. Gravitational Potential Energy
Kinetic Energy Preview
Kinetic Energy is the energy of motion or
energy in use
 Any matter in motion has Kinetic Energy
 There are many forms of Kinetic Energy
 Some forms include: light (radiant),
thermal (heat), sound (acoustic), electrical,
and mechanical

Thermal Energy
All matter is made up of atoms
 Atoms are in constant motion
 Thermal energy (heat) is all of the kinetic
energy due to the random motion of atoms
 Thermal energy also depends upon the
amount of atoms that are moving

Solids
 The
atoms in an
ice cube vibrate
in fixed positions
and do not have
a lot of kinetic
energy.
Liquids
 Atoms
of water
in a lake can
move more
freely and have
more kinetic
energy than
atoms in ice do.
Gas
 The
atoms of
water in steam
move rapidly, so
they have more
energy than the
particles in liquid
water or ice do.
Thermal Energy (cont’d)
Thermal
energy depends
upon the amount of atoms
that are moving.
 Consider,
a cup
of tea and the
water in a bath
tub.
 Both are the
same
temperature.
 Which has more
thermal energy?
?
 The
?
?
?
?
?
?
water in the bathtub has
more thermal energy.
 Why?
 Simply because it has more water
molecules.
Conduction

Conduction is the transfer of energy
through matter from particle to particle.

It is the transfer and distribution of heat
energy from atom to atom within a
substance. Conduction is most effective in
solids-but it can happen in fluids.
Conduction (cont’d)
 For
example, a spoon in
a cup of hot soup
becomes warmer
because the heat from
the soup is conducted
along the spoon.
Conduction (cont’d)
Have you ever noticed that
metals tend to feel cold?
 Believe it or not, they are not colder!
 They only feel colder because they
conduct heat away from your hand.
 You perceive the heat that is leaving your
hand as cold.

Conduction (cont’d)

Some items are conductors, they conduct
heat well. Example: metal

Some items are insulators, they DO NOT
conduct heat well. Examples: fabric,
wood, wool, and some plastic
Think about it . . .

What do we use a
“cooler” for?

What do we use a
coffee mug for?

Differences /
Similarities?
Convection
Convection is the transfer of heat by the
actual movement of the warmed matter.
 Heat leaves the coffee cup as the currents
of steam and air rise.
 Convection is the transfer of heat energy
in a gas or liquid by movement of currents.

Convection (cont’d)
Convection is responsible for making
macaroni rise and fall in a pot of heated
water.
 The warmer portions of the water are less
dense and therefore, they rise.
 Meanwhile, the cooler portions of the water
fall because they are denser.

Mechanical Kinetic Energy

Kinetic Energy = the energy of an object
due to the object’s motion

All moving objects have kinetic energy

Kinetic Energy depends on Mass and
Speed
Mechanical Kinetic Energy (cont’d)

KE = mass x speed x speed divided by 2

The greater the mass of a moving object,
the more Kinetic Energy it has.

The faster something is moving, the more
Kinetic Energy it has, also.
Mechanical Kinetic Energy

Which animal has the
bigger mass?

Which animal is able
to move faster?

Which animal has the
greatest KE?

KE = mass x speed2
2
Calculate the Mechanical Kinetic
Energy (KE)

KE = mass x speed2
2


Mass = 0.2 kg
Speed = 2 meters/sec

KE = 0.4 J
Mechanical Kinetic Energy

KE = mass x speed2
2
Mass = 4000 kg
 Speed = 2 meters/sec
(Note that the elephant is
going the same speed as
the mouse.)


KE = 8000 J
What effect does an increase of speed
have on Mechanical Kinetic Energy?

The green and yellow cars have the same
mass (1,200 kg)

The green car is traveling at a speed of 20
m/sec

The yellow car is traveling at a speed of 30
m/sec

Calculate their Kinetic Energies

KE = mass x speed2
2
Which car has the most KE?


Green car’s KE = 240,000 J
Yellow car’s KE = 540,000 J

Speed has a greater effect on
KE than mass because in the
equation speed is squared.

In other words, the faster an
object is going . . . the more
KE is has.
Practice Calculating KE

Use Joules (J) as the unit for Kinetic Energy

Tools: meter tape, stop watch, scale,
calculator

KE = mass x speed2
2
Electrical Energy

Electrical Energy is
the energy of moving
electrons.

Electricity is the flow of
electrical power or
charge.
Electrical Energy (cont’d)

It is a secondary energy source which means
that we get it from the conversion of other
sources of energy, like coal, natural gas, oil,
nuclear power and other natural sources, which
are called primary sources.
Electrical Energy (cont’d)

The energy
sources we use to
make electricity
can be renewable
or non-renewable,
but electricity itself
is neither
renewable or nonrenewable.
Two types of electricity:
Static and Current

Static electricity is
usually caused when
certain materials are
rubbed against each
other, like wool on
plastic or the soles of
your shoes on the
carpet.

It is the attraction of two
objects because one has
a positive charge and the
other has a negative
charge.
Two types of electricity:
Static and Current

The flow of
electrons is
called an electric
current
Look familiar?

Some items are conductors, they conduct
electricity well. Example: metal

Some items are insulators, they DO NOT
conduct electricity well. Examples: fabric,
wool, wool, and some plastic
Semiconductors

Some items are
semiconductors.

The ability of a
semiconductor to
conduct electrictiy is
between the ability of a
conductor and an
insulator.
A dimmer switch is a
semiconductor.
Resistors
Resistors resist the flow of electrons.
 They are really good at transforming
electrical energy into other forms of kinetic
energy (sound, light, heat).
 We find resistors in radios,
light bulbs, and ovens.

Sound or Acoustic Energy
 Sound
Energy
is caused by
an object’s
vibration.
Sound is a type of energy made by vibrations.
 When any object vibrates, it causes movement
in the air particles.
 These particles bump into the particles close to
them, which makes them vibrate too causing
them to bump into more air particles.
 This movement, called sound waves, keeps
going until they run out of energy.
 If your ear is within range of the vibrations, you
hear the sound.

Sound Energy (cont’d)

Picture a stone thrown
into a still body of water.

The rings of waves
expand indefinitely.

The same is true with
sound.
Sound Energy (cont’d)

Irregular repeating sound
waves create noise

While regular repeating
waves produce musical
notes
Sound Energy (cont’d)

When the vibrations
are fast, you hear a
high note.

When the vibrations
are slow, it creates a
low note.
Playing the Guitar



Stretching a guitar
string, stores potential
energy in the string
Letting it go causes
the potential energy
to be transformed into
kinetic energy
This makes the string
vibrate
Playing the Guitar (cont’d)



The vibrating string
transfers some of this
energy to the surrounding
air
The vibrating air travels to
your ear
When this energy reaches
your ear, you hear the
guitar
Radiation
Electromagnetic waves that directly
transport ENERGY through space.
 Sunlight is a form of radiation that is radiated
through space to our planet.
 The sun transfers heat through 93 million miles
of space.
 The energy travels through nothingness! No
matter required!

Radiant Energy
Radiant energy is energy in the form of
electromagnetic waves.
 Radiant energy can travel through a
vacuum.
 Examples of radiant energy = visible light,
infrared light, microwaves, radio waves,
ultra violet light, X-rays, and gamma rays.

Light Energy

Light energy is produced by
the vibrations of electrically
charged particles.

Unlike sound energy, the
vibrations that transmit light
energy do not need to be
carried through matter.
Light Energy (cont’d)


In fact, light
energy can move
through a
vacuum (an area
with no matter).
Also known as
visible light
energy.
Nuclear Energy
Nuclear Energy is the energy that comes
from changes in the nucleus of an atom.
 A lot of potential energy is stored in the
nucleus of atoms
 When two nuclei join together, or when a
nucleus splits apart, a lot of energy is
released. This is nuclear energy.

Nuclear Energy (cont’d)

Fusion = The joining of two
nuclei. This happens on the
sun.

Fission = The splitting of a
nuclei. Fission is used in
nuclear power plants to
generate electrical energy.
How are Kinetic and
Potential Energy
Related?
Law of Conservation of Energy




Energy can not be created or destroyed
It can be transformed, or changed, from one
form to another
Kinetic Energy can be transformed into Potential
Energy or other types of Kinetic Energy, and vise
versa. This can and does happen many times.
The total amount of energy doesn’t change.
Dynamic Mechanical Energy



Imagine a juggler
Sometime the objects
have a lot of kinetic
energy
Sometimes the objects
have a lot of potential
energy

A book on a shelf ledge has potential energy.

It has stored the energy that it took to lift it to the shelf.

If the book is bumped and it falls, the potential energy
changes to the kinetic energy of motion.
 When
does the book
have the most
potential energy?
 When
does the book
have the most kinetic
energy?
Forms of Kinetic Energy

Mechanical

Sound or Acoustic Energy

Thermal Energy or
Heat Energy

Light or Radiant Energy

Electric Energy

Nuclear Energy
Review
 Energy
 Work
is the ability to do work
is the transfer of energy
 Energy
cannot be created or
destroyed, but it can change form
Potential Energy Review

We learned about three kinds of Potential
Energy
1. Elastic
Potential Energy
2. Chemical Potential Energy
3. Gravitational Potential Energy
Review (cont’d)
 Potential
Energy is energy of position,
shape, or condition
 Gravitational
Potential Energy
depends on weight and height
 GPE
= Weight (N) x Height (m)
Review (cont’d)
 Kinetic
 It
Energy is energy of motion
depends on speed and mass
Review (cont’d)

Energy exists in many forms

Each form has its own characteristics

Some of the forms of kinetic energy we
learned about were: mechanical, thermal,
electrical, sound or acoustic, light or
radiant, and nuclear energy