Transcript Energy - Cloudfront.net

Work and Power Notes
What Work and Power are not…


Work is not where you go to earn a check!
Power is not how strong you are!
Work-Energy Theorem
Work is a transfer of energy that
occurs when a force makes an
object move in a direction parallel to
and opposite the force.
Doing work on an object
gives it energy!
Is work being done?
What 2 conditions must be present in order for work to
be done?
(1) there must be a force
(2) there must be movement or motion
Formula for work:
W
(Joules)
W
=
Fd
(Newtons)(meters)
=
F d (cosθ)
Work and Energy are both
measured in Joules because they
are related!
Power
Amount of work done in
a certain amount of
time.
(i.e. how fast you do work).
Formula
P (Watts) =
W (Joules)
t (seconds)
Roller Coaster Connection
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Work is done on the roller coaster when it
is lifted by the lift chain (machine) to the top
of the first hill.
That is how it is given potential energy!
If the lift chain is faster, it is more powerful.
Energy
Mechanical Energy



Energy is the ability to do work or make
something change.
Energy is measured in Joules (J).
Two main types: potential and kinetic
Potential Energy

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
Energy of position (stored energy)
Gravitational potential energy (GPE)
is due to how high something is .
GPE = mgh
Chemical potential energy is due to
the position of charges (includes
nuclear).
Elastic potential energy is due to the
position of something stretchy.
Kinetic Energy



Energy of motion, how fast it is going
Almost all other forms of energy are due to
the motion of something: electrical
(electrons), solar(photons/waves),
light/radiant (photons/waves), thermal
(molecules), sound (molecules)
KE = 1/2mv2
Law of Conservation of Energy
Energy can’t be created or
destroyed, but it can change form.
 Sometimes we say energy is
“LOST” but it is not lost, it is
converted to something else less
useful (heat)
 Formula
KEi + PEi = KEf + PEf
½mv²i + mghi = ½mv²f + mghf

Roller Coaster Connection
 The
ball has the greatest
potential energy (PE = mgh)
at the top of the first
(highest) hill.
 It is not moving there so it
has no kinetic energy.
Roller Coaster Connection - Conservation
Kinetic energy (KE = 1/2mv2) is
at its highest when the roller
coaster is the fastest.
 This occurs at the lowest point
of the roller coaster because
that is where all PE is converted
to KE (there is no potential
energy at that point h=0)

Of course in the real world…
 Both
air resistance and friction act on
the roller coaster, transforming some
of the kinetic energy to thermal energy
(heat).
Designing a roller coaster:
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What force drives a roller coaster?
What keeps a roller coaster going?
Why does the first hill for a roller coaster
have to be the highest?
Where is the only place work is done on a
roller coaster (except to stop it)?
How can you increase the power on a
roller coaster?
Energy Transformations
Station 1
 Food
contains chemical
energy which we turn into
kinetic energy.
 We eat food to obtain energy
from the bonds.
Station 2
 The
rubber band will go flying if
you stretch and then release it.
 This is a conversion of elastic
potential energy to kinetic energy.
Station 3
 The
rubber ball has
gravitational potential
energy when you hold the
ball.
 Gravitational PE is
converted to kinetic energy
when you drop it.
Station 4
 Radiant/light
energy from the light bulb
is converted into kinetic energy to
make the flags of the radiometer spin.
 The light bulb also converts electrical
energy from the outlet to radiant and
thermal energy.
Station 5
 The
mechanical energy of spinning
the hand generator handle is
converted to electrical energy.
 The electrical energy is then
converted to radiant and thermal
energy, lighting the light bulb.
Station 6
Chemical energy in the battery
is converted to electrical energy
that travels down the wire and
is converted to kinetic energy
when the handle of the hand
generator spins.
Station 7
The chemical energy of the
gasoline is converted to thermal
energy and kinetic energy as
the car moves around the track.
Station 8
Chemical Energy in the lemon is
converted to electrical energy.
Station 9
Radiant energy is converted to
electrical energy to power the
calculator.
Station 10
The roller coaster’s gravitational potential
energy at the top of the hill is converted to
kinetic energy on the way down.