Download Energy

Energy
NASA
What is energy?
Your textbook defines energy as the ability
to make something happen…
Teachengineering.com
Vital Imagery, Itd
More precisely in physics energy is the
ability to do work…
Energy of Motion
Mechanical Energy
Other forms of energy
Potential Energy
Stored energy…
Energy can be transformed from
one type to another…
Electrical
Light
Thermal
Energy can be transferred from one
object to another….
Practice identifying energy
transformations…
…as a class  powerpoint…
…as individuals  worksheet…
Lets look specifically at the
energy of motion…
farnes.com
Mechanical Energy
…the energy of motion
Mechanical Energy
ME = PE + KE
Potential Energy
Kinetic Energy
PE
KE
Gravitational Potential Energy
…the potential energy that an object has because it is
high up above the ground.
Gravitational Potential Energy
Height
MASS
Weight
g (acceleration of
gravity)
Which has more potential energy: a 5-kilogram
pumpkin that is 1 m above the ground or a 1-kilogram
pumpkin that is 1 m above the ground? Explain.
The pumpkins are both at the same
height above the ground. Therefore
the 5 kg pumpkin has more
gravitational potential energy
because it has more mass.
Which has more potential energy: a 5-kilogram
pumpkin that is 1 m above the ground or a 5kilogram pumpkin that is 10 m above the ground?
Explain.
Both pumpkins have equal mass.
Therefore the pumpkin that is 10 meters
above the ground has more gravitational
potential energy because it is higher.
Gravitational Potential Energy
PEgrav
Unit for Energy
joules (J)
C H Jeaens, Nature, 26, 616 (1882)
Kinetic Energy
Anything that is moving has
kinetic energy
Kinetic Energy
Speed (velocity)
Mass
Which has more kinetic energy: a Matchbox™
car that is moving at 5 m/s or a real car that is
moving at 5 m/s? Explain.
Both cars are moving at the
same speed. The real car,
however, has more mass
and therefore has more
kinetic energy.
Which has more kinetic energy: a 15 kg child
that is walking at 1 m/s or a 15 kg child who is
running at 3 m/s? Explain.
Both children have the same mass.
The child who is running at 3 m/s
therefore has more kinetic energy
because he/she is running faster.
Bouncing Ball
Hig
hPE
Low
KE
Hig
hPE
Hig Low
hPE KE
Low
KE
Low
PE
Low
PE
Hig
hKE
Hig
hKE
PE
KE
As we have already seen…
What about friction?
CONSERVATION OF
ENERGY!!!!
The Law of Conservation of Energy
Energy can neither be created nor
destroyed…
…but may be transferred from one
object to another and transformed
from one type to another.
Apply conservation of energy
to motion
PE
KE
At which point would the roller coaster have the most potential
energy?
The roller coaster would have the most
gravitational potential energy at point A
because it is the highest above the ground.
At which point would the roller coaster have the most kinetic
energy?
The coaster would have the most kinetic energy
at point B. All of the potential energy has been
transformed into kinetic energy and the coaster
is moving the fastest at this point.
At which point would the roller coaster be moving
the fastest?
The coaster will be moving the fastest at point B
Why does the first hill have to be the highest?
In the real world…there is FRICTION!!!
Some of the mechanical energy transforms
in to thermal energy through friction -heating up the track…
With less mechanical energy, the car can only
rise to heights lower than the first hill.
KE and PE of a roller coaster
http://www.hkphy.org/oceanpark/rol/resource/rollercoaster_e.ht
ml
Roller Coaster (link on website)
How can we reach the top of the
first hill?
Must somehow add total mechanical
energy to the system.
We do this in the form of “work.”
Why do roller coasters eventually stop?
Must transfer mechanical energy from the
coaster to the track…
…usually friction transforms mechanical
energy to thermal energy.
…the coaster transfers energy to the
track….the track heats up…and the
coaster slows down…
Today’s Activity: Small Group
Presentations of
PE
KE
explorecrete.com (Bungee.gr)
Freshpowder.com
Squaw Valley Olympic Photos
geewocka
Let’s look at an example…
• Draw a picture
• Make charts of KE, PE, and total ME for 45 locations on picture
• Present to class describing changes in KE,
PE, and ME
• Watch video and provide commentary…
Roller Coaster – Draw a Picture
(on larger whiteboard)
Draw KE, PE, and ME Charts
(use small whiteboards)
Watch video and provide commentary
Your turn to consider other
examples where energy
transforms between kinetic
energy and potential energy.
Bridge swinging
The Skatepark
Bungee jumping (giant spring)
Ski-jumping
Linerider
See class website for a link to this game…where
you can create your own roller coaster..
Also on website…link to Phet
physics animations…
Phun – also on website