Energy What is energy?

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Transcript Energy What is energy?

What is energy?
Energy comes in many forms that we are
familiar with.
• Definition: energy – a measure of the
ability to do work.
•Energy is measured in Joules (J)
Hey… Work has the same unit as energy!
Thermal & Light Energy
• Energy comes in many forms…
Definition: mechanical energy – energy that can
be used to do physical work.
• Examples:
 Sound Waves
 Objects in Motion (kinetic)
Definition: chemical energy – energy stored in the bonds
of atoms.
• Examples:
 Burning Gasoline
 Batteries
 Food
Definition: electrical energy – energy
resulting from the flow of electrons.
 Electricity
 Lightning
Definition: radiant energy – energy travelling as
electromagnetic waves.
 Sunlight
 Heat
Energy is very closely related to work. In fact…
• Energy must be transferred to do work!
It takes energy to do pretty
much anything.
Energy is constantly flowing
through the universe.
When you pull a rubber band back, you are
doing work on the rubber band.
By doing that work, you are transferring some
of your energy into the rubber band.
You used energy to do the
work that stretched the
rubber band!
Now, the rubber band has
the energy you used!
Mechanical Energy comes in 2
Great-Tasting Flavors!
Potential Energy
When you stretched the rubber band, the energy you transferred to it
was held as “potential energy”…
• Definition: potential energy – the stored
energy that results from an object’s
position or condition.
Potential Energy
When an object is stretched or
compressed, it has “elastic” potential
Potential Energy
When an object is above the ground, it
has “gravitational” potential energy.
We will focus on GPE.
Gravitational Potential Energy
GPE depends on mass and height of an
The GPE equation:
•PE = mgh
 m = mass (kg)
 g = gravitational acceleration (9.8 m/s2)
 h = height (m)
In the example with the rubber band…after you released the rubber
It had kinetic energy as it snapped back into place.
• Definition: kinetic energy – the energy an
object has because of its motion.
Only MOVING objects have
kinetic energy!
What would happen to a bottle cap if the rubber
band hit it?
Kinetic Energy
Kinetic Energy!
The kinetic energy equation:
KE = ½ mv2
m = mass (kg)
v = velocity (m/s)
Higher velocity gives increases your KE
more than a higher mass.
•This is because velocity is squared!
What happens to energy??
When you hit a baseball, what happens to the energy
that you transferred to the bat?
Did the energy disappear, or did it just change into
other forms…?
What happens to energy??
When you hit the baseball, the kinetic energy of the
swinging bat is transferred to the baseball.
The baseball flies away!
What happens to energy??
Energy is also used to produce the cracking
And some energy is used to heat up the bat and
the baseball!
What happens to energy??
• What happened with the baseball is an example of
a very important law…
The Law of Conservation
of Energy.
• The Law of Conservation of Energy states:
It is always
Energy can change forms!
What point has the most PE?
What about the most KE?