Transcript Kinetic energy.

Chapters 3 & 4
Objectives
• Recognize how energy causes change.
• Describe common forms of energy.
• Illustrate that the two general types of
energy are kinetic energy and potential
energy.
Different Forms of Energy Have
Different Uses
• Energy takes on many forms.
• Lamps use electrical energy while plants
use energy from the sun to grow.
Energy
• All forms of energy have one important
point in common--- they cause change to
occur.
• The flow of electrical energy through a
wire causes a cool, dark bulb to get hot
and glow.
• You are a source of energy that makes
changes in your environment!
What in this picture is using energy?
Forms of Energy
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Mechanical Energy
Sound Energy
Chemical Energy
Thermal Energy
Electromagnetic Energy
Nuclear Energy
Mechanical Energy
• Energy that moves
objects is mechanical
energy.
• The energy that you
use to put book on a
shelf is mechanical
energy, s is energy
that a person uses to
turn car key.
Sound Energy
• Vibrations of particles
• When you hear a car
drive by, you are
detecting vibrations in
the air produced by
sound energy.
• Cannot travel through
empty space.
Chemical Energy
• Energy that is stored in chemical
compositions of matter.
• Example: When wood or gasoline burns,
chemical energy produces heat.
• The energy used by your body cells
comes from chemical energy.
Thermal Energy
• The total amount of
energy from the
movement of particles
in matter is thermal
energy.
• The energy of this
motion in an object is
the object’s thermal
energy.
Electromagnetic Energy
• Transmitted through space in the form of
electromagnetic waves.
• Include visible light, x-rays, and
microwaves.
• The sun releases a large amount of
electromagnetic energy, some of which is
absorbed by Earth.
Nuclear Energy
• The center of an
atom– it’s nucleus– is
the source of nuclear
energy.
• When a heavy atom’s
nucleus breaks apart
or when the nuclei of
two small atoms join
together, energy is
released.
Nuclear Energy
• Everything has a beginning, and nuclear energy is no
exception. The first reactor to use nuclear energy was
built in 1942. The discovery of fission, that lead to
nuclear energy, was discovered a few years earlier. A
man named Enrico Fermi first discovered fission. In
1934, Fermi proved that neutrons could split atoms. This
was breaking news. The particles made by these splits
were lighter than the original atom. Later the scientist
added up the particles, and still it weighed less than the
original product. This proved that Einstein's theory was
right, that some of the mass changed to energy. This
theory was none other than e=mc2. The uses of this
energy would be great. From cities, to ships, to bombs,
nuclear energy powers them all.
Kinetic Energy
• The energy of motion is called Kinetic
energy.
• Kinetic energy increases as mass
increases.
– For example is a bowling ball and a soccor
ball were moving at the same speed, the
bowling ball would have more kinetic energy
because of its greater mass.
Kinetic Energy
• Kinetic energy increases as speed
increases.
– If two identical bowling balls were rolling along
at different speeds, the faster one would have
more kinetic energy because of its greater
speed.
Potential Energy
• Potential Energy is the stored energy that
an object has due to its position or
chemical composition.
• P. 75-76
Review
• Give three ways you use energy. How
does each example involve a change?
• What two factors determine an object’s
kinetic energy?
How can potential energy be
changed into useful forms of
energy?
Energy can change forms but is
NEVER Lost!
• Potential energy is stored in the chemicals
on the head of a match. The flame of a
burning match releases that energy as
light and heat. Where does the energy to
strike the match come from in the first
place.
Energy Changes Forms
• Matches chemical energy stored can be
changed to light and heat.
• Photosynthesis
• Page 78
Conversions between Potential
Energy and Kinetic Energy
• Potential energy can be changed into
kinetic energy and back into potential
energy.
• Page 79
Using Energy Conversions
• Page 80-81
Energy is Always Conserved
• As the soccer ball rolls, it rubs against the
ground. Some kinetic energy changes into
heat because of friction.
• Some of the ball’s energy changes to
sound energy as you hear the ball roll.
• Although the ball loses kinetic energy, the
overall amount of energy in the universe
does not decrease.
Energy is Always Conserved
• In the soccer ball, the ball loses energy,
but this energy is transferred to other parts
of the universe. Energy is conserved.
• The Law of Conservation of Energy- states
that energy can neither be created nor
destroyed.
• Balance of Energy
Energy Conversions may produce
unwanted forms of energy
• When energy
changes forms, the
total amount of
energy is conserved.
• However, the amount
of useful energy is
almost always less
than the total amount
of energy.
Energy Efficiency
• Energy Efficiency is a measurement of
usable energy after an energy conversion.
• Example: Energy-efficient house-hold
appliances. These appliances convert a
greater percentage of energy into the
desired form than inefficient forms.
Review
• Describe an energy conversion you have
observed in your own life.
• What is the Law of Conservation of
Energy?
• Give an example of an energy conversion
that produces unwanted forms of energy.