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Chapter 15
Energy
Cow Power
Without a supply of energy to run our millions of machines, society as
we know it would cease to exist! Because of our reliance on fossil fuels,
supplies of coal, gas, and oil are dwindling. But the ability to convert from one
form to another may yet save our way of life, An unusual source of
energy may save us upto 300,000 barrels of oil a year- cow power!!
In a mutualistic relationship, owners of cow feedlot and 250,000
head of cattle are supplying a power plant in California with about
1500 metric tons of cow manure a day. Once manure is scraped out of the
feedlots, it is piled in long, wide berms, sprinkled with line, and dried for later use.
The manure is fed into the plants combustor and is passed down a series
of platforms or hearths to dry. Escaping gases are recaptured and burned,
reducing emissions from the plant. The hot manure is then burned, and the
burning manure heats up an adjacent boiler to produce steam. The steam
turns a turbine, which turns a generator to produce electricity.
The electricity is then sold to a power company. Cow manure is readily
available, easily obtained, and cheap source of fuel for the production of electricity.
Thank a cow - it may be providing more than just a glass of milk in the near future.
Section 1
Energy and Its Forms
Key Concepts
• How are energy and work related?
• What factors does the kinetic energy of an
object depend on?
• How is gravitational potential energy
determined?
• What are the major forms of energy?
Energy and Work
• Energy is the ability to do work.
• In other words, energy is transferred by a
force moving an object through a distance.
• When work is done on an object, energy is
transferred to that object.
• Both work and energy are typically
measured in joules (J).
Kinetic Energy
• The energy of motion
• The kinetic energy of any moving
object depends upon its mass and
speed.
• Formula:
1 mv2
Kinetic energy (KE)= 2
m= Mass
v= Velocity
• A 70.0-kilogram man is walking at a speed
of 2.0 m/s. What is his kinetic energy?
• A 1400-kilogram car is moving at a speed
of 25 m/s. How much kinetic energy does
the car have?
• A 50.0-kilogram cheetah has a kinetic
energy of 18,000 J. How fast is the
cheetah running? (Hint: Rearrange the
equation to solve for v.)
Kinetic Energy
• Notice that doubling the mass in the
formula would double the kinetic energy.
However, doubling the speed would
quadruple the kinetic energy, since kinetic
energy is proportional to the square of an
object’s speed.
Potential Energy
• energy that is stored as a result of position
or shape.
• Two forms of potential energy are
gravitational energy and elastic
potential energy.
When this musician pulls
the string of her cello to
one side, the string is
stretched and gains
potential energy.
Gravitational Potential Energy
• Potential energy that depends upon an
object’s height
• An object’s gravitational
potential energy depends on
its mass, its height, and the
acceleration due to gravity.
This diver has
gravitational potential energy
as she stands at the end of a
diving board.
Gravitational Potential Energy
• Formula:
Potential energy (PE) = mgh
m= mass
g= gravity
h= hieght
The acceleration due to gravity, g, has
a value in SI units of 9.8 m/s2 on Earth.
Elastic Potential Energy
• The potential energy of an object that is
stretched or compressed
• Something is said to be elastic if it springs
back to its original shape after it is
stretched or compressed.
A compressed bicycle shock
absorber and a wound-up toy
robot both have elastic
potential energy.
Forms of Energy
• 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.
Mechanical Energy
• The energy associated with the motion
and position of everyday objects
• 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.
Thermal Energy
• Almost all of the matter around you
contains atoms.
• 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
Energy occurs in many
forms. This molten metal is
extremely hot. It contains a
Great deal of thermal energy
Chemical Energy
• the energy stored in chemical bonds
• When bonds are broken, the released
energy can do work.
• All chemical compounds, including fuels
such as coal and gasoline, store energy.
This family is using the
chemical energy of burning wood
to produce thermal energy for
heating marshmallows.
Electrical Energy
• the energy associated with electric
charges.
• Electric charges can exert forces that do
work.
• Electrical energy also occurs in nature.
• CD players, flashlights, and calculators.
Lightning bolts transfer
electric charge.
Electromagnetic Energy
• a form of energy that travels through
space in the form of waves.
• Visible light and X-rays
• Because electromagnetic waves can travel
long distances through air and space, they
are often used for communication.
Galaxies are giant structures in
space that typically contain billions
of stars. The stars give off
enormous amounts of
electromagnetic energy
Nuclear Energy
• 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 is a process that releases energy
by splitting nuclei apart.
• Nuclear fusion, releases energy when less
massive nuclei combine to form a more massive
nucleus.
Reviewing Concepts
• 1. Describe the relationship between work and
energy.
• 2. How is the kinetic energy of an object
determined?
• 3. What factors determine the gravitational
potential energy of an object?
• 4. Give an example of each of the major forms of
energy.
• 5. When you heat a pot of water over a flame,
what form of energy is added to the water?