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THE ABILITY TO CAUSE CHANGE
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mechanical energy
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types of energy
Thermal energy - due to temperature (recall
that this comes from the motion of
molecules, so it is really kinetic energy)
Heat energy -transfer of thermal energy
Chemical Potential Energy - stored in
chemical bonds
Nuclear energy - stored in the nuclei of an
atom
Electrical energy - EM interactions
Radiant energy -carried by EM waves
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Energy
• Energy is the capacity (ability)
to do work.
• Kinetic Energy: Associated with
an object in motion
• Potential Energy: Present in an
object that has the potential to
move because of its position
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Kinetic Energy
• Motion
• KE of an object depends
upon two variables:
1. the mass (m) of the
object
2.the speed (v) of the
object.
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Calculating Kinetic Energy
A formula to find
the kinetic energy
of any body
based on its
velocity.
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Potential Energy
•An object
can store
energy as
the result
of its
position.
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Forms of potential energy
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Gravitational Potential Energy
• GPE is the energy stored in
an object as the result of
its vertical position (i.e., height).
• Amt. of GPE is dependent on
two variables:
1.the mass
2.the height
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Calculating Gravitational
Potential Energy
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Elastic Potential
• Elastic PE is
the energy
stored in
elastic
materials as
the result of
their
stretching or
compressing.
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Conservation of Energy
Energy cannot be created or
destroyed…only changed from one
form to another.
The total energy of an isolated
system remains constant (isolated
systems have no external forces
and no mass changes)
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ENERGY BEFORE = ENERGY AFTER
Energy can be changed from one
form to another, but it does not
disappear.
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Mechanical Energy
• The motion of some objects
contain a combination of only
kinetic and potential energies.
• ME is the sum of the KE and forms
PE associated with a system
• Therefore, ME= KE + PE
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Conservation of Energy
TOTAL ENERGY OF THE SYSTEM REMAINS THE
SAME
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Conservation of Energy
TOTAL ENERGY OF THE SYSTEM REMAINS THE
SAME
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Conservation of Mechanical Energy:
Therefore,
MEi = MEf
KEi + PEi = KEf + PEf
½ mvi2 + mghi = ½ mvf2 + mghf
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Conservation of Mechanical Energy:
• Conservation of ME only hold
true when the only energies
of the system are KE and PE.
• Therefore, in the presence of
friction energy is transformed
to other types of energies.
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Energy Conversion
When one type of energy is changed or transformed into
another type of energy
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Examples
Battery
Can you think of More?
Create a graphic organizer to illustrate energy
conversions. draw a picture to represent four different
energy conversion you may encounter in everyday life.
Be sure to explain what type of energy it starts with and
what type of energy it ends with.
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Energy Conversion
clip
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What about a falling object?
What happens when it hits the ground?
Where did the energy all go?
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•As it is falling and when the object hits the ground the energy
is converted into other types of energy such as:
•sound energy (waves), Light Energy (sparks), thermal
energy due to friction (heat) in the ground and air,
vibrations in the earth (energy waves.)
•If the object bounces, some energy is converted
momentarily into elastic potential energy.
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If Robin Hood had been Written by an Engineer....
And Robin didst slowly and with great determination put
potential energy equal to the work of his muscles into an elastic
storage device.
And therewith Robin the Bold and Valiant didst convert this stored
energy most quickly, efficiently, and accurately into the velocity of a
sturdy and pointed dart (oft called arrow) such that almost all of its
former potential energy didst become kinetic. Then this speedy dart
didst split an arrow (oft called dart) already buried in most distant
target, having been previously hurled there at an equally great speed
by a similar conversion of stored energy.
EOCT Questions
Which statement about energy is true?
A Energy can be increased in a closed
system.
B Energy cannot be conserved.
C Energy can be decreased in a closed
system.
D Energy cannot be created nor destroyed.