Download Energy Chapter 5

Energy
Chapter 5
What is Energy 5.1
Energy
is the ability to do work or
cause change
Work is done when a force
moves an object through a
distance.
W = F x D
Work and Energy
 When
an object or living thing does work on
another object, some of its energy is
transferred to that object
Therefore:
Work can be thought of as the
transfer of energy.
 When
energy is transferred, the object upon
which the work is done gains energy.
 Energy
work)
is measured in Joules (same unit as
Power and Energy

Power is the rate at which work is done

If the transfer of energy is work, then power is
the rate at which energy is transferred OR the
amount of energy transferred in one unit of time
Power
= Energy transferred
Time
Power & Energy

Power is involved whenever energy is being transferred.

Calm breeze vs. Tornado
 Power
of both is the rate of energy transfer to lift a
leaf a certain distance
 Tornado
has the same energy transfer, but with more
power because it transfers the energy at a quicker
rate.
Types of Energy

Two basic types of energy
 Kinetic
 Potential
 Type
of energy depends on if the object is
moving or not.
A
moving object can do work when it strikes
another object and moves it some distance
 The
energy an object has due to its motion is
called kinetic energy
Greek
word kinetos = moving
Factors affecting Kinetic Energy (KE)
 Kinetic energy depends on
Mass
Velocity
 KE increases as mass increases
 KE increases as velocity increases
Calculating KE
 KE
= ½ x mass x velocity
 Does
2
changing the mass and velocity have the
same affect on KE?
 NO – changing the velocity has a greater
effect on KE than changing the mass by the
same factor.
 WHY? – because velocity is squared.
 Therefore, doubling the mass will double
the KE, but doubling the velocity will
quadruple the KE.
Potential Energy (PE)

An object does not have to be moving to have energy

Some objects have stored energy

Result of their shapes or positions
 Lift
a book off the floor to your desk
 Compress
 Energy
a spring to wind a toy.
has been transferred to those objects in both examples and is
stored.
 May
be used later when the book falls to the floor or the spring
unwinds.

Stored energy as a result of shape or position of an object is potential energy.

This type of energy has the “potential” to do work.
Gravitational Potential Energy (GPE)
 Defined
as potential energy related to
an objects height.
 GPE equaled to the work done to lift
the object
Recall: work = force x distance
 The force used to lift the object
equals the weight of the object
 The distance the object is moved is
the object’s height
Gravitational Potential Energy (GPE)
Formula
GPE
to calculate GPE
= mass x gravity x height
Simplified

as GPE = weight x height
REMEMBER: weight = mass x force of gravity
Gravity
On Earth = 9.8 m/s2
Example:
Calculate
 If
the ski jump is 40m high, what is the GPE
of the
Green
skier = 600N
Red
Skier = 500N
500
Newtons x 40m = 20,000 J GPE
600
Newtons x 40m = 24,000 J GPE
Elastic Potential Energy (EPE)

An object gains a different type of potential
energy when it is stretched

Elastic potential energy – the potential energy
associated with objects that can be stretched or
compressed
Formula to calculate Elastic potential
energy
EPE
=½
2
kx
Chapter 5-2
Forms of Energy
 Energy
comes in many forms
Mechanical energy – associated with the
position and motion of an object
A combination of potential and kinetic
Calculation:
Mechanical Energy = Kinetic energy +
Potential Energy
Example of ME calculation

A football thrown by a quarterback has BOTH PE and KE.
The higher the ball is thrown the greater the PE, the
faster it is thrown the greater the KE.

PE = 32J

KE = 45 J

Mechanical Energy (ME) = 77J (32+45)

An object with mechanical energy can do work on another
object

Mechanical energy is the ability to do work.

The more ME an object has the more work it can do.
Other forms of energy
 These
other forms are associated with the
particles that make up objects.
 These
particles are too small to be seen. (atoms &
molecules)
Thermal
energy
Electrical
energy
Chemical
energy
Nuclear
energy
Electromagnetic
energy
Thermal energy
 All
objects are made up of atoms and
molecules
 Atoms and molecules are in constant
motion – therefore they have kinetic
energy
 Atoms and molecules are arranged
differently in different objects –
therefore they have potential energy
Thermal Energy
 Total
PE and KE of particles in a substance =
thermal energy
 Example Melting ice cream
Fast moving particles in warm air, make
the particles in the ice cream move
faster, as the kinetic energy of the ice
cream particles increases, the thermal
energy increases. The ice cream melts.
Electrical energy
The
energy of electric charges
Depending
on whether the charges
are stored or moving, EE can be
kinetic or potential.
Chemical Energy
Almost
everything is made up of
chemical compounds
Chemical compounds are made up
of atoms and molecules
Bonds between the atoms and
molecules hold the compounds
together
These chemical bonds have energy
Chemical Energy
 CE is the energy stored within the
chemical bonds of substances.
• Food we eat
• Matches
• Cells in our body
 When bonds break, chemical energy
is released and new compounds may
form
Nuclear Energy

A type of potential energy

Stored in the nucleus of an atom

Released during a nuclear reaction

Nuclear fission – occurs when a nucleus of an atom is
split
 Used
in nuclear power plants
Nuclear Energy

Nuclear fusion – occurs
when the nuclei of
atoms join together
 Occur
continuously
in the sun, release
tremendous
amounts of energy
Electromagnetic Energy

Sunlight is a form of Electromagnetic energy

Travels in waves

EM waves have both electrical and magnetic properties

Examples
 Microwaves
 X-rays
 UV
radiation
 Infrared
 Radio
radiation
waves
5.3
Energy Transformation and Conservation
 Niagara
Falls
A
center for a
network of electrical
power lines
 Water
above the falls
is used to generate
electricity.
Energy Transformations
 The
mechanical energy of moving
water can be transformed into
electrical energy.
 Most forms of energy can be
transformed into other forms of
energy.
 A change from one for of energy to
another is called: energy
transformation
Single Transformations
Multiple Transformations
 Often
a series of transformations are needed to
do work
A match
Mechanical - Thermal - Chemical -
Thermal - Electromagnetic
 The ME used to strike the match is transformed
into TE. TE causes the particles in the match to
release stored chemical energy, which is
transformed into TE and the EME seen as light.
Multiple Transformations
A
car engine
EE produces a spark- TE of
spark -> releases CE in fuel - CE
turns into TE - TE converted
into ME & EE
Transformations between Potential and
Kinetic Energy
Transformation
between Potential
energy and Kinetic energy is the
most common form of
transformation.
Any object that rises and falls
experiences a change in its kinetic
and gravitational potential energy.
Energy transformation in juggling
Decreasing KE as it
rises
No motion at its
highest point, no KE,
maximum PE
PE decreasing, Rising
KE
In motion = KE
High KE
No motion = no KE,
ball has PE
Energy transformation in a pendulum
Pendulum continuously
transforms energy from
kinetic to potential and
back.
Conservation of Energy
 The
law of conservation of energy states:
When
one form of energy is transformed
to another, no energy is destroyed in the
process. Energy cannot be created or
destroyed
The
total amount energy is the same
before and after any transformation. If
you add up all the new forms of energy
after a transformation, all the original
energy will be accounted for.
Energy and friction

Scenario: If you set a spinning top in motion, will it stay
in motion forever?
 WHY?
 As
the top spins, in encounters friction with the
surface it is spinning on and with the air.
 Whenever
a moving object experiences friction,
some of the KE is transformed into TE.

The fact that friction transforms mechanical energy into
thermal energy explains why no machine is 100% efficient.
 Output
work is always less than input work in a real
machine.
Energy and matter

Albert Einstein’s Theory of Relativity

During some nuclear reactions, matter is converted to
energy.

Einstein showed that energy and mass are equivalent and
can be converted into one another.

E = mc2 is the equation to calculate the amount of energy
that is created when matter is destroyed.

Matter = anything that has mass and takes up space
5.4 Energy and Fossil Fuels
Earth 400 million years ago

Lush green swampy
forest

Enormous dragon flies

Huge cockroaches
Formation of Fossil Fuels
 Fuel
– a material that contains stored
potential energy
Ex.
Gasoline used in cars, propane used
in grills
 Fuels
used today were formed hundreds of
million of years ago.
 These
fuels include:
Coal,
petroleum, and natural gas
Known
as Fossil Fuels
Formation of Fossil Fuels
 Vast
ancient forests were the source of
coal
When plants and animals died, their
remains piled up in thick layers in
swamps and marshes
Clay and sediment covered their
remain
Over time, increased pressure and
temperature turned their remains into
coal
Energy from the sun
Energy
is conserved
Meaning: fuels do not create
energy
Fossil fuels store energy
Where did they get the
energy from?
The sun
Energy from the sun
 Fossil
fuels contain energy that came from the
sun
 The
sun is the source of energy for most of
Earth’s processes
Within
the dense core of the sun – the
process of nuclear fusion –> nuclear energy is
transformed into electromagnetic energy as
well as other forms.
Some
of this electromagnetic energy reaches
the Earth as light.
The Sun’s energy on Earth
When
the sun’s energy reaches
earth
Plants, algae, and certain
bacteria - transform some of the
light into chemical energy
Some of the energy in the
chemical compounds they make
is used for their daily needs. The
rest is stored.
The Sun’s energy on Earth
Animals
eat plants – store some
of the plants chemical energy in
their cells
When the animals and plants
died – some of the energy stored
is trapped within them
This trapped energy is the
chemical energy found in coal.
Use of Fossil Fuels
 Fossil
Fuels can be burned to release
the chemical energy stored millions of
years ago.
 Burning fuels is known as combustion
 During combustion, chemical energy is
transformed to thermal energy
 Thermal energy can heat water to
produce steam.
Ex. Modern coal fired power plants:
 Steam
is raised to a high temp in a boiler –
leaves the boiler with high pressure – turns a
turbine
 A turbine is a fan connected to an axle – steam
causes the blades of the fan to turn very fast –
thermal energy is converted to mechanical
energy.
 Turbines are connected to generators that
produce electricity.
 Chemical
–> thermal –> mechanical -> electrical
Coal-fired power plants