Download Energy Transformation PowerPoint

05/04/2017
Energy Transformations
• law of conservation of energy
• friction
• As the ball moves upward,
gravity pulls it and its
speed and KE decrease,
but the PE (gravitational
PE) is increasing because
the ball’s height is
increasing.
• At the ball’s highest point,
the GPE is greatest, and
the ball’s kinetic energy is
the lowest.
Energy Can Change Forms
The Law of Conservation of Energy:
energy cannot be created or destroyed, it
can only be transformed from one form to
another.
• As the ball moves
downward, PE decreases.
At the same time, the ball’s
kinetic energy increases.
• When the ball reaches the
player’s hand again, its KE
is at the maximum value
again.
• When it stops in the
player’s hand, KE is zero,
while PE is high.
Example 1:
Changes between KE and PE:
Throwing a basketball
• When the player is
holding the ball, the KE
of the ball is zero. It
does have GPE
because if its height
above the ground.
• As the ball is thrown
upward, it has a lot of
KE.
Example 2:
Changes between KE and PE:
A pendulum
• When the ball is
at rest, it has
some PE
because it is
suspended off
the ground.
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• When the ball is
pulled back and
held at the
starting position,
what happens to
the energy of the
ball?
• PE increases, KE
is zero.
• When the ball is
released, what
happens to the
energy of the
ball?
• KE increases, PE
decreases.
• When the ball is
swinging and has
reached the mid
point, what
happens to the
energy of the ball?
• KE is at its
maximum, PE is at
its lowest. It still
has some PE
because it is
suspended off the
ground.
• When the ball is
swinging and has
reached the highest
point on the other
side, what is the
balls energy?
• KE is zero (the ball
stops moving as it
begins to swing
back the other way).
PE is at its
maximum.
Describe the
energy at point A.
Describe the
energy at point B.
Describe the
energy at point C.
Describe the
energy at point D.
A: the coaster is
stopped at the top. Its
PE is highest, KE is
zero.
B: As the coaster rolls
downward, the PE is
converted into KE.
C: KE is highest, PE is
lowest.
D: The car slowed
down as it climbed up.
KE decreased, PE
increased.
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Could the cars
ever have enough
energy to reach
another point as
high as point a?
No, the car slows
down and cannot
reach that height
again.
If energy cannot be
destroyed, what
causes the cars to
slow down?
The cars slowed
down because of
friction. As the car
slid along the track,
friction caused
some of the energy
to be converted into
thermal energy.
Energy can be lost when it is
converted into thermal energy.
Friction is a force that resists the
sliding of two surfaces that are touching.
Friction and the Law of
Conservation of Energy
• What type of energy does a moving
bicycle have?
• What happens to mechanical energy
when you apply the bicycle brakes and
the bicycle stops?
• A moving bicycle has mechanical energy.
When you apply the brakes, the bicycle’s
mechanical energy is not destroyed.
Friction and the Law of
Conservation of Energy
(cont.)
• The mechanical energy is transformed into
thermal energy. Friction between the brake
pad of a car and the moving wheel
transforms mechanical energy into thermal
energy (heat). The car slows down.
• There is always friction between any two
surfaces that are rubbing against each
other.
• EX: Rubbing hands.
Using Energy
• When you use energy, you usually
change it from one form into another.
• All forms of energy can be transformed
into thermal energy.
friction
from Latin fricare, means “to rub”
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Using Energy (cont.)
What happens to energy when
it is used?
Using Energy (cont.)
• When energy changes form, some
thermal energy is always released.
• Scientists often refer to thermal energy
that cannot be used as waste energy.
• Whenever energy is used, some energy
is transformed into useful energy and
some is transformed into waste energy.
Using Energy (cont.)
• Using Thermal Energy:
– All forms of energy can be transformed into
thermal energy.
• a gas stove transforms the chemical energy in
gas to thermal energy.
• An electric heater transforms electricity into heat
• A jet engine burns fuel, releasing thermal energy
from chemical energy, and then transfers the
thermal energy into mechanical energy.
Using Energy (cont.)
• Using Chemical Energy:
– Plants convert radiant energy (light) into
chemical energy that is stored in the
chemical bonds of glucose molecules.
– When animals eat glucose, they release the
chemical energy from the food and
transform it into kinetic energy and thermal
energy (body heat).
Using Energy (cont.)
• Using Radiant Energy:
– Solar panels transform radiant energy into
electrical energy.
– Talking on your cell phone: Cell phones
receive radiant energy (microwaves that are
sent from the cell phone tower to your
phone) and transforms it into electrical
energy to power the speaker. The speaker
transforms the electric energy into sound
energy.
Waste Energy
• Energy transformation is not efficient.
• Whenever energy is transformed, some
is lost to the surroundings as heat
energy.
– Your cell phone gets hot
– Light bulbs get hot
– Car engines get hot
• When energy is lost during
transformation, it is called waste energy.
It does NOT disappear, but transforms
into a type of energy not being used.
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