Energy
What is energy?
• Energy is something that can cause things to
move or to change.
• Where is energy found?
• Energy can be found everywhere.
• How can you tell that an object has energy?
• When I see it move.
Energy is…
• The ability to perform work or to change an
object.
Work is…
• The measurement of the energy used to
perform a task.
Why is no work being done when someone is
pushing a car but it is not moving?
• Work is only done when the object that is
receiving the force moves from one location
to another.
What is potential energy?
• The energy that is stored in the position or the
structure of an object.
• Think of a stretched spring. It has energy, but
it’s not moving. It has the potential to do
work. The energy is stored.
Forms of potential energy
• Chemical potential energy
• Elastic potential energy
• Gravitational potential energy
What is chemical potential energy?
• This is the energy in the links between atoms
and molecules.
• Food contains energy stored in the chemical
bonds between atoms.
Elastic Potential Energy
• This is the energy stored by something that
can stretch or compress.
• Name an example of this type of energy.
• A stretched rubber band
• A stretched slingshot
• Some watches
What is Gravitational Potential Energy?
• This is the energy an object possesses due to
its position above Earth’s surface.
• Why is a boulder on a hill an example of
gravitational potential energy?
• Anytime an object is raised above the ground,
it gains gravitational potential energy.
Would a large boulder or a small boulder at the same
height above the ground have more gravitational
potential energy?
• A large boulder would have more gravitational
potential energy. Why?
• The greater the object’s weight and height
above the ground, the more gravitational
energy it gains.
What do all the forms of potential energy have
in common?
• All the forms of potential energy have the
ability to do work.
• What is different about the types?
• The different forms of potential energy are
due to different kinds of forces such as gravity,
mechanical, and chemical.
A weight lifter lifts a barbell above her head and
holds it there. What can you infer about the
work she is doing?
• Since the weights are not moving above the
weight lifter’s head, she is not doing any work.
What type of potential energy exists when you are on a
diving board high above the swimming pool.
• Gravitational potential energy
What is kinetic energy?
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This is the energy of a moving object.
What is an example of this type of energy?
A moving car
A rolling ball
A roller coaster moving
The amount of kinetic energy an object has
depends on the object’s velocity.
• An example is trying to knock down bowling
pins with a tennis ball and with a bowling ball.
Which ball would knock down more pins?
• The bowling ball of course!
• Why?
• Because the bowling ball has a greater mass
than a tennis ball.
List some forms of kinetic energy.
• Heat- vibrations of particles.
• Electricity- related to the kinetic energy of
electrons
• Sound- particles move in waves
• Light- moves in the form of waves
• All forms of energy have one
thing in common- they can
perform WORK!
Can potential energy change to kinetic
energy?
• Yes. Potential energy can easily change to
kinetic energy.
• Think of a bow used to shoot arrows.
• The stretched bow has potential energy.
• As soon as the bow is released the potential
energy changes to kinetic moving the arrow.
Which has more kinetic energy- a ball
moving at 4 m/s or a ball moving at
5 m/s?
•The ball moving at 5 m/s
has more kinetic energy.
Which can do more work- a 3 kg bowling ball
moving at 2 m/s or a 5 kg bowling ball moving at
2 m/s?
• The 5 kg bowling ball has more kinetic energy
and can do more work.
A roller coaster stops at the top of a hill.
What can you infer about its kinetic
energy?
• Since the roller coaster is not moving, it does
not have any kinetic energy.
What is the law of conservation of
energy?
• Scientists believe that energy cannot be
created or destroyed; it only changes form.
• A roller coaster does not destroy energy as it
slows down. The energy becomes heat and
sound through the work of friction.
A dropped ball doesn’t bounce back to its starting
height. How does this situation fit the law of
conservation of energy?
• The dropped ball does not bounce back to its
starting height because some of its kinetic
energy has changed into heat and sound
energy due to friction.
How might the heat energy in an oven perform
both desirable and undesirable work?
• You might want the oven to do work by baking
bread. On a hot summer day, the oven might
also do undesirable work by adding more heat
to a home that is already hot inside.