Transcript 8th Energy Unit

Energy Unit
Adapted from Motion, Forces, and Energy textbook
Copyright 1997 Prentice-Hall Inc.
What is Energy?
What is energy?
Energy is not matter.
Matter is anything with mass and volume
We now know how to change matter into
energy though. How?
We live in an ocean of energy. Energy is
all around us, we are surrounded.
Energy
Energy:
The ability of something to cause change
The ability to do work
Measured in joules (j)
Unit: Energy (j) same as work (j)
5 Forms of Energy
5 forms of energy:
1. mechanical
2. heat
3. chemical
4. electromagnetic
5. nuclear
Mechanical Energy
Mechanical Energy
Energy associated with motion
Heat Energy
Heat Energy
The internal motion of the atoms is
called heat energy.
The faster the atoms move the more
heat energy they have.
Rub hands together mechanical to heat
Chemical Energy
Chemical Energy
Energy required to bond atoms
together.
bonds are broken,
chemical energy is released
Electromagnetic Energy
Electromagnetic Energy
Moving electric charges
Nuclear Energy
Nuclear Energy
Nucleus -(protons and neutrons)
nucleus splits, nuclear energy is
released in the form of heat and light
energy
Potential Energy
Potential Energy (PE):
Stored energy due to position
Examples: rock on a cliff, battery, food,
gasoline, stretched rubber band, apple
hanging in a tree
Elastic Potential Energy
Elastic PE:
Energy stored by something that can
stretch or compress (ex. rubber band,
spring)
Ex: shoot an object with rubber band.
Farther you stretch the rubber band,
the faster the object travels, therefore
greater KE.
Elastic Potential Energy
Do rubber bands have energy to do work?
(un-stretched rubber bands no energy)
Stretch rubber band—Does it have energy to do work?
(stretched rubber bands have energy)
Where is the energy when the rubber band is stretched?
(it is in the rubber band)
What happens to the energy when the rubber band is
released?
(it is converted into motion -- KE)
Gravitational PE
Gravitational PE (GPE):
Energy stored by objects that are above
the earth’s surface (objects that can fall)
Depends on mass, acceleration and height
GPE increases with height
Gravitational PE
GPE = mass  gravity  height
GPE = m g h = weight  height
GPE = m (kg)  9.8 m/s2  h (m)
j = 1 Nm
Kinetic Energy
Kinetic Energy (KE):
Energy in the form of motion
Depends on mass and velocity of
moving object.
Object in motion has ability to do work
Kinetic Energy
KE = ½ mass  velocity2
KE = m  V2
2
(j) = (kg)  (m2/s2)
1 j = 1 kg m2/s2
Kinetic Energy
Double mass and you double energy
Double velocity = 4 times the KE
As velocity is squared, increase
velocity and KE greatly increases.
Which would hurt more? Double mass of bowling
ball or double the velocity? Explain.
PE: 354kJ
KE: 0kJ
V: 0m/s
h=70m
Roller Coaster
Potential energy
PE: 0kJ
KE: 354kJ
V: 37.1m/S
PE: 0kJ
KE: 354kJ
V:
37.1m/S
becomes Kinetic
energy.
Kinetic
energy can
become
Potential
177kJ
energy. PE:
KE: 177kJ
h=35
V: 26.2m/S
m
Energy analogy
When energy is transferred, it can transform
(change form) but it still remains energy.
Analogy:
How is energy like money?
When money is transferred from one person or
place to another it can change form (transform) but
it still remains money.
Energy Transformations (ball)
Demonstrate: how bounce height of ball becomes lower
and lower each time it bounces. Have students infer
why this happens.
Each time the ball bounces, part of its energy is
transformed into other forms of energy, such
as thermal (heat) energy, sound energy and
vibrations in the ground. In addition, some
energy is absorbed by the ball. Therefore, it
will never bounce as high as the initial drop
height.
Energy Transformations
Ex: A light bulb is a device that transforms
electrical energy into electromagnetic (light)
energy and thermal energy
Chemical energy (coal)
heat energy
(burn to create steam)
mechanical
energy (steam is used to turn turbines)
Electromagnetic energy
(generates electricity)
heat energy
(blow drier, oven)
Law of Conservation of Energy
The law of Conservation of Energy:
Energy cannot be created or destroyed.
It may be transformed from one form
into another; however, the total amount
of energy in the universe remains
constant. (Transformers)
Law of Conservation of Energy
Energy conversions occur without a gain or
loss in energy
Energy into a system = energy out of a system
Due to friction, energy might seem to be lost,
but it has changed into thermal energy.
.
Bibliography
staffweb.psdschools.org/jbarnaby/8_pwr
pt/Energy%20unit%20pwr%20point.ppt