March 18, 2013
Forms of Energy
Energy Sources
Potential Energy
Kinetic Energy
Nuclear Energy
Electricity
Heat
Sound
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March 18, 2013
Do Now:
How are energy and work related?
Energy is the ability to do work; work is a transfer of energy.
What is the difference between kinetic and potential energy?
Kinetic energy is the energy of motion, and potential energy is an object's
energy due to its position or shape.
Explain why a high-speed collision might cause more damage to vehicles
than a low-speed collision.
A high-speed collision would cause more damage to vehicles because
the vehicles would have more kinetic energy due to their high speed KE =
mv2/2. The vehicles would do more work on one another, resulting in
large amounts of damage.
March 18, 2013
Produced
Thermal Chemical Electrical
Sound Light
heat;
particles
moving
according
to
temperatur
e
vibrations of
electrically
charged
particles;
don't cause
other
particles to
vibrate.
two or
more
nuclei join
together;
one
nucleus
splits apart
K/P/M K
Nuclear
breaking/
joining
chemical
bonds
moving
electrons
vibrations
of a
material
that cause
vibrations
of air
molecules
P
M/P/K
M/K/P
K
P
music;
instrument
s
light
nuclear
energy;
Result/
Use
burning,
heat/ temp
food
change
energy
electrical
devices,
power
Example
wood
burning,
steam;
frozen lake gasoline,
sugar
guitar
light bulbs;
strings;
power
piano
plants
strings
sun;
microwave
nuclear
light
power
stars
plants
March 18, 2013
**Speed has a greater impact on kinetic energy than does mass
because speed is squared. When mass doubles, kinetic energy
doubles. But when speed doubles, kinetic energy quadruples.
The term "speed" is used here because the object's direction does
not matter.
March 18, 2013
Kinetic energy = mv2
2
Gravitational potential energy= (weight) (height)
Mechanical Energy = potential energy + kinetic energy
March 18, 2013
What determines an object's thermal energy?
An object's thermal energy depends on its temperature, the arrangement
of its particles, and the number of particles in the object.
Describe why chemical energy is a form of potential energy.
When a substance forms, work is done to bond particles of matter
together. The energy that creates the new bonds is stored in the
substance as potential energy.
Explain how sound energy is produced when you beat a drum.
When you beat a drum, you give it mechanical energy by moving the
drumskin back and forth (vibrating). The vibrations cause air particles to
vibrate, transmitting energy that results in sound.
When you hit a nail into a board using a hammer, the head of the nail
gets warm. In terms of kinetic and thermal energy, describe why you
think this happens.
The kinetic energy of the moving hammer is transferred to the head of the
nail, causing particles in the nail to move faster. The faster the particles
move, the greater their thermal energy.
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1. What is an energy conversion?
An energy conversion is a change from
one form of energy to another. Any
form of energy can be converted into any
other. form of energy.
2. Describe an example in which
electrical energy is converted into
thermal energy.
In an iron, electrical energy is
converted into thermal energy.
3. Describe an energy conversion
involving chemical energy.
When you light a natural-gas stove, the
chemical energy in the natural gas is
converted into thermal energy.
4. Describe the kinetic-potential energy
conversions that occur when you bounce
a basketball.
When you bounce a basketball, you give
it kinetic energy. At the moment the ball
hits the ground, its kinetic energy is
greatest and its potential energy is zero.
At that moment, the change of shape of
the ball that occurs when it hits the
ground gives the ball some potential
energy that is used when the ball moves
back upward. When the ball bounces
back up toward your hand, its kinetic
energy is converted into potential energy
because its position changes. At the
moment the ball is at the top of its
bounce, its kinetic energy is zero.
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What is the role of machines in energy conversions?
Machines can transfer energy from one object to another as
they make work easier. For example, when you use a crowbar
to remove a hubcap, you transfer energy to the crowbar, and
the crowbar transfers energy to the hubcap. The way the
energy is transferred determines how much easier the work
is to do.
Give an example of a machine that is an energy converter,
and explain how the machine converts one form of energy to
another.
Sample: A wind turbine converts the kinetic energy of wind
into electrical energy.
A car that brakes suddenly comes to a screeching halt. Is
the sound energy produced in this conversion a useful form
of energy? Explain your answer.
The sound energy of the screeching is not a useful form of
energy because it cannot be used to do work.
March 18, 2013
Describe the energy conversions that take place in a pendulum, and
explain how energy is conserved.
Potential energy is converted to kinetic energy, kinetic to potential, and
both potential and kinetic to thermal energy because of friction. All
energy is conserved because some energy becomes thermal.
Why is perpetual motion impossible?
In every system, some of the energy put in is converted to thermal energy
that is waste energy. A machine cannot run forever unless energy is
continually added.
Imagine that you drop a ball. It bounces a few times, but then it stops.
Your friend says that the ball has lost all of its energy. Using what you
know about the law of conservation of energy, respond to your friend's
statement.
Energy isn't lost in the entire system of the ball, the ground, and the air
around the ball; it is converted into other forms.
March 18, 2013
particles moving
according to
temperature
breaking/joining
chemical bonds
two or more nuclei
join together; one
nucleus splits apart
moving electrons
vibrations of a
material that cause
vibrations of air
vibrations of
electrically charged
particles