Transcript School Paper

Energy
Types
Forms
Transformations
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• The higher and object goes, the greater
the PE. Imagine the difference between
having a tennis ball dropped on your
head from 3 cm and from 30! The PE of
the ball changes to KE as it falls and you
will notice a big difference when it
collides with your head!
OUCH!
• The greater the mass of an object the
greater the PE as its height increases.
Imagine having a tennis ball dropped on
your head from 1 meter and a bowling
ball from one meter!!
KE and PE
transformations
• PE can be transformed into KE...
Transformations in a roller coaster
Let’s consider KE and
PE in a roller coaster
PE is greatest and KE is lowest
here as it slows at the top.
PE is lowest
here and
increases as
the car rises
(gains height).
PE is lowest
again here and
KE greatest
here.
Kinetic energy is converted to potential
energy as the car rises, so kinetic energy is
decreasing while potential energy is
increasing.
Potential energy is converted to kinetic
energy as the car falls, so potential energy
is decreasing while kinetic energy is
increasing.
At what positions would
there be…
1.
2.
3.
4.
5.
The greatest potential energy?
The least potential energy?
The greatest kinetic energy?
The least kinetic energy?
What’s wrong with this roller coaster?
Here’s another example
– a pendulum
Where in the swing of the pendulum
would the bob…
1. Have the greatest potential
energy?
2. Have the least potential
energy?
3. Have the greatest kinetic
energy?
4. Have the least kinetic energy?
5. Where is the change from KE
to PE occurring?
6. Where is the change from PE
to KE occurring?
pendulum
KE + PE must remain
constant
• KE and PE must be the same for the entire system.
This is the
Law of Conservation of Energy.
Energy cannot be created or destroyed –
it can only be transformed. The total
energy in a system always adds up to
the same amount.
But, in the real world…when energy is transformed
from one type to another a bit of the energy is always
transformed to thermal energy by friction.
The image is taken from:
Robertson, W. C. Stop Faking It: Energy. 2002.
Illustration by Brian Diskin
How do we calculate
GPE?
• GPE is the energy an object
has due to position and shape.
• It depends on an object’s
weight and height.
GPE = weight x height
Joules = Newton x meters
http://en.wikipedia.org/wiki/James_
Prescott_Joule
I have a book sitting on a book shelf 1.5 m off
the ground. The book weighs 50 N.
1. How much PE does it have? How much
KE?
2. If I knock the book off the shelf, how much
PE does it have at 1 m? How much KE
does it have?
3. How much KE does it have just before it
hits the ground?
The image is taken from:
Robertson, W. C. Stop Faking It: Energy. 2002.
Illustration by Brian Diskin
How do we calculate
KE?
• KE is the energy an object has
due to motion.
• It increases with mass and
speed.
KE = ½ mv2
mass
velocity or
speed
• So which factor matters more? Mass or
velocity?
Example
• I have a book sitting on a book
shelf 1.5 m off the ground. The
book weighs 50 N. How much PE
does it have? How much KE?
• If I knock the book off the shelf, how
much PE does it have at 1 m? How
much KE does it have?
• How much KE does it have just
before it hits the ground?
• A tennis ball has a mass of 0.60 kg
and rolls along the ground with a
velocity of 10 m/s. What is the
tennis ball’s KE?
A car stopped at the top of a
ramp has
a. heat energy
b. potential energy
c. kinetic energy
d. mechanical energy
Which represents kinetic energy?
a. A bear standing in a field of berries
b. A salmon resting in still water
c. A bear holding a salmon it has caught
d. A salmon leaping up a waterfall
Forms of Energy
• Read pages 447-451 of your textbook
and look in the NEED Intermediate
Energy Infobook at the different forms
of energy.
• Define the different forms and provide
examples.
Which Forms of Energy
are represented?
The pictures on the previous page
are from:
• Light bulb
http://idowns.net/Picture/Goods_Photo/2009/0220/Light_
bulb_picture_quality_material___3_90.html
• Batteries
http://commons.wikimedia.org/wiki/File:01__Set_of_Energizer_Batteries.jpg
• Speakers
http://concertspeakers.org/
• Sunrise
http://projectvisual.net/2008/09/sunrise-pictures/
• Matches
http://www.justinnewitter.com/stock/Matches1.JPG
• Fire
http://3.bp.blogspot.com/_XjCWZ6A7feA/TEUgLYiSpKI/A
AAAAAAABb0/vwWpW6ihTKo/s1600/campfire.jpg