Download Conservation of Energy

Conservation of Energy
Everything that happens in the universe
involves some kind of energy transformation.
Every energy transformation comes with a cost.
Energy is defined as the ability to do work,
which commonly means to bring about
changes in our environment.
Conservation of Energy
In physics: work is done when an object is
pushed or pulled through a distance.
The exertion of a force does not guarantee
that you are doing work.
You must actually be moving something
with your force!
Many things that we commonly think of as “work”
do not qualify under the definition in physics.
Conservation of Energy
Jed leans against
the brick wall.
Ned pushes hard
against it to the
point of
exhaustion.
Who, if anyone,
is doing work?
Conservation of Energy
The amount of work done is proportional to
the force used.
It takes twice as
much work to
lift two books.
W∝F
Conservation of Energy
Work is also proportional to the distance the
object is moved.
It takes twice as
much work to
push one book
twice as far.
W∝d
Mathematical Definition of Work
Units of Measurement
Work
is measured in
Joules.
Force
is measured in
Newtons.
Distance
is measured in
Meters.
W = F·d
1 Joule = (1 Newton) x (1 meter)
Conservation of Energy
Energy is the ability to do work.
In situations where
an object clearly has
the potential to do
some work, but
hasn't done it yet, we
say the object has
potential energy.
Forms of Energy
A heavy object that has been raised to a great height
has the potential to fall. It could do a lot of
useful work (or a lot of damage.)
Gravitational
potential energy is
stored in this pile
driver.
Equation for Gravitational Potential
Energy
Forms of Energy
Energy of motion is called kinetic energy.
This 18-wheeler,
moving at 100 km/h
has 2.2 million
joules of kinetic
energy.
Equation for Kinetic Energy
Conservation of Energy
When the girl drops the book, energy is
transformed.
All of the potential
energy the book
had at the top is
changed to kinetic
energy by the time
it gets to the
bottom.
Conservation of Energy
With a rescue net
below, firemen
encourage a woman
to leap from a
burning building.
At first, all of her
energy is in the form
of gravitational
potential energy.
Conservation of Energy
After falling 1/4th of
the way down, 1/4th
of her potential
energy has turned
into kinetic energy.
The other 3/4th of her
energy is still in the
form of potential.
Conservation of Energy
After falling ½
way down, ½ of
her energy is
potential, the
other half is
kinetic.
Conservation of Energy
3/4th of her original
energy has now
turned to kinetic
energy. Only 1/4th
of it remains as
potential energy.
Conservation of Energy
When our lady friend arrives at the
bottom, all of what was once her potential
energy has turned into kinetic energy.
All of her original energy is still
present. It has simply changed form.
Conservation of Energy
The total amount of energy remains the same.
Conservation of Energy
At points A and C,
the pendulum has
all gravitational
potential energy.
At point B, the
energy is all in the
form of kinetic.
Energy Graph for the Simple
Pendulum
Conservation of Energy
The girl lets go of the
bowling ball but remains
standing in the same
place. Will she be struck
by the ball when it
swings back?
The Law of Conservation of Energy
The sum total energy of all the parts of any
process remains the same.
Energy cannot be created or destroyed.
It can be transferred (moved) or transformed
(changed from one kind to another), but the
total energy always remains the same.
The Work-Energy Principle
Work is an energy transfer. Work reduces
the energy of the system doing the work and
increases the energy of the system on which
the work is done by the same amount.
In the end, all the energy is accounted for.