Transcript Energy & Waves w Pix

Objective 1: Relate the
Conservation of Energy to
energy transformations
Describe how energy--mechanical, electrical,
chemical, light, sound, and heat--can be
transformed from one form to another
Show understanding that energy
transformations result in no net gain or loss
of energy, but that in energy conversions less
energy is available due to heat loss.
Apply Conservation of
Energy
Apply the concept of conservation and
transformation of energy within and
between organisms and the environment-such as food chains, food webs, and
energy pyramids
Apply the concept of conservation and
transformation of energy to other
everyday phenomena.
Objective 2: Relate waves
to the transfer of energy
Relate wavelength to energy
Relate frequency to energy
Relate wavelength to frequency
Describe how waves travel through
different kinds of media
Mechanical waves
Water, Sound, Slinky, etc.
Electromagnetic waves
Describe how waves can be
destructive &/or beneficial
Describe how waves--earthquake waves,
water waves, and electromagnetic waves-can be destructive (harmful) or beneficial
(good) due to the transfer of energy
Destruction (cons)
Benefits (pros)
ALL WAVES
Transfer energy from one
place to another
Energy transferred does NOT have mass.
Actual particles of the wave (such as water
waves) are NOT transferred, but stay in the
same place
Have wavelength, frequency, amplitude
SHORTER WAVELENGTH means HIGHER
FREQUENCY AND ENERGY!
Longitudinal vs. Transverse
Compression waves
where one part of a
medium smashes into
another
Wave particles travel
parallel to the energy
SOUND WAVES are
longitudinal. They
cannot travel in space
because there is no
medium
Up and down waves,
like wiggling a rope
back and forth
Wave particles travel
perpendicular (at right
angles) to the energy
being transferred
Electromagnetic waves
are transverse!
LINK TO SIMULATION
Mechanical vs. Electromagnetic
MECHANICAL WAVES:
Require a medium, or
something to travel
through (cannot travel
through space)
Water waves, waves in
a rope or slinky, and
sound waves are
examples
ELECTROMAGNETIC WAVES:
Require NO
medium, can travel
through outer
space!
ALL EM waves
travel at the
“speed of light”
3 x 108 m/s or
186,000 miles/sec
Electromagnetic waves,
from low to high frequency:
RADIO WAVES
LONG wavelength, LOW
frequency AND energy
MICROWAVES
INFRARED (HEAT)
v = f 
VISIBLE LIGHT
ULTRAVIOLET
SHORT wavelength, HIGH
X-RAYS,
frequency AND energy
GAMMA RAYS
link to applet
So for ALL electromagnetic waves…
As the FREQUENCEY gets higher, what
happens to the WAVELENGTH since the
SPEED is THE SAME for all EM radiation?
Wavelength gets SHORTER as frequency gets
higher, of course!
VISIBLE LIGHT
Only a SMALL band of the EM spectrum
Regular “white” light can be separated into all
the different colors with a prism
This was discovered by Isaac Newton!
RED (longest wavelength, lowest energy) to
VIOLET (shortest wavelength, highest energy)
ROY G BIV stands for Red, Orange, Yellow,
Green, Blue, Indigo, Violet
Electromagnetic vs Sound
ALL travel at the
“speed of light”,
186,000 miles/second
or 300,000,000 m/s
Transverse
Don’t need a medium
Can travel through
outer space, all
across the universe
Travels MANY MANY
times slower, only about
370 m/s (almost a million
times slower!)
Longitudinal
Require a medium
(mechanical)
Cannot travel through
outer space
Energy gets
dispersed(spreads out)
quickly
ENERGY
The ability to “do work” or make a
CHANGE in something
Energy has many forms, and all can be
transformed from one to another
There is a CONSTANT amount of energy
in any given closed system, even in the
universe as a whole!
ENERGY AND WORK
An “ideal system” means NO friction, and
no energy “lost” as heat
Energy is NEVER destroyed. It is only
“lost” if it becomes unusable
In an ideal system (or machine), you get
ALL the energy OUT that you had to put
IN. This is called 100% efficiency.
REALITY
There are NO “ideal
systems” in real life!
In REAL LIFE some
energy is ALWAYS
changed to “lost”
heat because of
friction!
ENERGY AND WORK UNITS
MASS is measured in kilograms [kg]
WEIGHT and other FORCES are measured
in NEWTONS [N]
ENERGY is usually measured in Joules [J]
WORK is usually measured in Newtonmeters [N m]
SINCE ENERGY AND WORK ARE EQUAL, A
JOULE IS EQUAL TO A NEWTON-METER!
POTENTIAL ENERGY
This is STORED ENERGY
Most commonly means GRAVITATIONAL
potential energy, or energy stored because
of a position HIGHER than some reference
point (like the ground)
Potential energy continued
Can be “ELASTIC” (OR “SPRING”)
potential energy, like the energy stored in
a stretched rubber band, the spring in a
wind up toy, or a drawn bow before
shooting an arrow
Link to applet force and energy in spring
Link to applet 2 spring and energy
CHEMICAL Potential Energy
Potential energy is
also stored in
batteries, as
CHEMICAL
potential energy!
 http://www.regentsprep.org/R
egents/physics/phys03/apotdif
/default.htm
POTENTIAL ENERGY continued
POTENTIAL ENERGY can also be stored up in
chemical bonds, such as in food (C bonds)
There is a tremendous amount of potential
energy in MASS ITSELF, as Einstein showed
with E = mc2
MASS itself is like VERY concentrated,
congealed energy!
Gravitational potential energy is described by
PE = mgh
or mass x gravity x height
KINETIC ENERGY
Energy of motion (kine- means MOTION, like
cinema means moving picture or movie!)
KE = 1/2 mass times velocity squared
If something is NOT MOVING,
is has ZERO KINETIC ENERGY!
IDEAL vs. REAL
In an “ideal system,”
ALL (or 100%) of the
WORK you put IN can
be changed to KE
(NO machine in real
life is anywhere close
to 100% efficient)
In real machines,
most energy is
changed to heat.
A car is only about
30% efficient! Only
30% of the gas gets
changed to KE!
 Where does the
other 70% go??
POTENTIAL energy example
If a rock has a mass of 5 kg, and it is on
a hill 2 m high, how much PE does it
have?
PE = mgh [or mass in kg x height in
meters]
g = 10 m/s/s
Solution
Weight in Newtons = mass in kg x gravity!
PE = weight in Newtons x height in
meters
so PE = 5 kg (10 m/s/s) (2m) = 100
Joules or 100 J !
PE Problems
1. If a 5 kg rock is lifted up
a 1 m hill, how much PE
does it have?
2. If a rock has has 20 N of weight
and sits on top of a 2 meter tall
box, how much potential energy
does it have?
PE Solutions
1. PE = mgh
so PE = 5 kg x 10 m/s/s x 1 m = 50 J
2. PE = weight x height
so PE = 20 N x 2 meters =40 J
Reminder: Weight = mass x gravity. For
example, 2 kg of mass X 10 m/s/s = 20 N!
Kinetic energy example
KE = 1/2 mass x
velocity squared
If a 3,000 kg car is
traveling at 10
m/s, how much KE
does it have?
Solution to KE problem
KE = 1/2 (3,000 kg) (10 m/s)2

= 1,500 (100) = 150,000 J!
Kinetic energy problems
1. If a 60 kg girl is
running at 5 m/s, how
much Kinetic energy does
she have?
2. If the girl stops and sits
on a bench to rest, how
much kinetic energy does
she have?
Kinetic energy solutions
1. KE = 1/2 mv2
so KE = 1/2 (60 kg) (5 m/s)2
so KE = 30 (25) = 750 J
2. KE = 1/2 (60 kg) (0 m/s)2
so KE = 0
She is not moving, so she has no Kinetic
energy while sitting on the bench!
transferred back and forth
If you do 20 J of WORK lifting a rock onto a
table, how much PE does the rock have?
If the rock then falls off the table, how
much KINETIC ENERGY does it have just
before it hits the floor?
Source of Energy
WHERE did the rock GET the kinetic
energy?
When the rock smashes into the floor,
where does the energy go?
KE if you double mass
If you had instead lifted a rock with TWICE
as much mass, how much more WORK
would you have put in to lift it?
How much more PE would it have had at
the top?
How much more KE at the bottom?
If you lifted more distance
If, instead of lifting a rock with twice the
mass, you lifted the SAME rock twice the
height, how much more WORK would you
have done?
What if you lifted a rock with TWICE the
MASS a distance TWICE AS FAR? How
much more Work would you have to do?
Spring or Elastic Potential
If you do 25 N m (or 25 J) of
WORK pulling back the
bowstring, how much SPRING
POTENTIAL ENERGY will the
bow then have?
Once you let the string go,
how much KINETIC ENERGY
will the arrow then have?
On a Roller Coaster...
... at what point is
your POTENTIAL
ENERGY greatest?
Where is your
KINETIC ENERGY
greatest?
Ignoring energy “lost” as heat due to
friction, what can you say about the
TOTAL amount of energy for the whole
ride on the roller coaster?
Roller Coaster continued
As you go DOWN a hill on the ride,
what kind of energy is being transferred
to what other kind?
As you go UP a hill on the ride,
what kind of energy is being transferred
to what other kind?
SOLAR ANIMATION
http://www.artescapesonline.com/movies
/stirling_solar_dish_animation.htm
LINK to energy transformation on a ski slope
http://www.glenbrook.k12.il.us/gbssci/phys/mmedi
a/energy/se.html
LINK to energy transformation of a dart
www.glenbrook.k12.il.us/. ../energy/dg.html
LINK to energy transformation on a roller coaster
www.glenbrook.k12.il.us/. ../energy/ce.html
Energy
transferred
How is energy
transferred from the
SUN, to you walking
down the sidewalk?
Transfer of energy
If you hit a baseball,
describe the energy
changes occurring.
You throw a ball into
the air. What energy
transformations are
taking place?
POWER
Power = Work / time
P = W / t
The unit for Power is the
WATT which is equal to a
N m / s or J / s
1 Watt = 1 N m / s = 1 J / s
1,000 Watts = 1 kilowatt
QUESTION:
Bob and Sue--2 people with
equal masses--each take
identical packages up a flight
of stairs. Sue runs really
fast, and Bob walks.
Who does more WORK?
Who uses more POWER in
the above situation? WHY?
MACHINES,
including simple
machines...
Make it EASIER to do a job by
allowing US to use LESS FORCE.
(We say the machine “multiplies”
our force.)
Machines may also allow us to
change the direction of our force, so
gravity works in our favor (like using
a pulley to get water out of a well).
Remember that
Work is Energy.
In an “ideal” system, Work
in = Energy out
Machines DO NOT
Both are in Nm or Joules
ALLOW US TO USE
If you use 10 J to lift a
LESS WORK OR
book up onto a table, the
ENERGY!!!!!!
book then has 10 J of
THERE IS NO FREE
gravitational potential
energy. How much Kinetic ENERGY, NO FREE
energy will it have if it
WORK, NO FREE
falls to the floor?
LUNCH!!!!!!!
6m
MA
3m
If you push a box up
the inclined plane, 6 m,
IMA =
instead of lifting it straight
di
Fo
up 3 m to the top, what is
----------The ideal mechanical
do = Fi
advantage?
IMA = distance in / distance out
or Force out / force in
6m/3m=2
Efficiency
6m
3m
If there is no friction,
what is the efficiency?
If the box weighs 20N,
how much work do you do if you lift it
straight up?
How much work if you push it up the plane?
How much FORCE (ideally) do you use
pushing it up?
Efficiency…
What is the IMA (or TMA)?
What if--in reality with real friction--it
ACTUALLY takes you 15 N to push the box
up…THEN what is the AMA and what is the
efficiency?
***Remember F out (load moved) divided
by F in (or done) gives MA
***Remember AMA/IMA = Efficiency
Solutions
Ideally you would only have to use 10N to push
the crate up the incline, since it weighs 20N
and the length of the incline is twice the height.
(6 m instead of 3 m.)
IMA (or TMA) is: 20N/10N = 2 or 6m/3m = 2
AMA is: 20N/15N = 1.33
Efficiency is:
1.33/2 = 0.665 or 67%
Mechanical Advantage of a
Pulley System
http://library.thinkque
st.org/CR0210120/MA
%20of%20PS.html