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Energy: The Ability to Do Work
Energy: The Ability to Do Work
• ENERGY is anything that has the ability to move
a sample of matter against a force.
friction
energy
• ENERGY can come in many different forms: light,
sound, electrical, chemical, heat, nuclear, and
mechanical.
Energy: The Ability to Do Work
• All energy can be in one of two states:
KINETIC OR POTENTIAL.
• Kinetic energy (KE) is the energy of the motion
of the sample of matter.
• When a sample of matter is moving, it has
kinetic energy.
Energy: The Ability to Do Work
• Potential energy (PE) is the energy due to the
position of the sample of matter.
• Potential energy is inactive or stored energy.
• Kinetic energy is active or released energy.
Energy: The Ability to Do Work
• Potential energy can be converted into kinetic
energy.
Energy: The Ability to Do Work
• Kinetic energy can be converted into potential
energy.
Energy: The Ability to Do Work
• The pendulum at the Parthenon in Paris shows
the relationship between KE and PE.
the
wire
The
weight
Energy: The Ability to Do Work
Pendulum pulled
back in order to
begin motion.
Pendulum at top
of back swing.
Maximum PE.
Maximum PE.
Lowest KE
Highest PE
Lowest KE
Highest PE
Highest KE
Pendulum at bottom of swing.
Lowest PE
Maximum KE.
Energy: The Ability to Do Work
• Skateboarders also demonstrate the conversion
of kinetic energy to potential energy and back to
kinetic energy.
Energy: The Ability to Do Work
Lowest KE
Highest PE
Lowest KE
Highest PE
Medium KE
Medium PE
Medium KE
Medium PE
Highest KE
Lowest PE
Energy: The Ability to Do Work
• The kinetic energy of an object is determined
by its mass and its speed.
1) The faster an object moves, the
greater its kinetic energy will be.
2) The more massive an object is, the
greater its kinetic energy will be.
A speeding bullet can have the same KE as a creeping truck .
Energy: The Ability to Do Work
• The potential energy of an object due to gravity
is determined by its mass and its height off the
ground.
1) The higher an object is off the ground,
the greater its potential energy will be.
2) The more massive an object is, the
greater its potential energy will be.
A truck and a penny can have the same PE.
Energy: The Ability to Do Work
• The potential energy of an object due to a spring
is determined by the distance the spring is
stretched or compressed and the spring’s force
constant.
1) The more the spring is stretched or compressed, the
greater its potential energy will be.
2) The greater the spring’s force constant is, the its
potential energy will be.
A bullet in a spring gun can have the same PE as a person on a pogo stick .
Energy: The Ability to Do Work
• A change in temperature alters the average
speed of the particles in a sample of matter,
thus a change in temperature causes a change
in kinetic energy.
low temperature
solid
high temperature
solid
vibrating
slowly
vibrating
quickly
Energy: The Ability to Do Work
• A change in phase alters the positions of the
particles in a sample of matter, thus a change
in phase causes a change in potential energy.
solid at 80oC
ordered, fixed
positions
liquid at 80oC
disordered, changing
positions
Energy: The Ability to Do Work
• According to the Law of Conservation of Energy,
energy can neither be created nor destroyed
but can change from one form to another without
changing the overall amount of energy present.
Thus the total energy of a system must remain
constant. There is a conservation of energy!
battery
chemical energy
electrical energy
light energy & heat