Download GEO-PHYSICAL SCIENCE 2011-2012 Mr. Sacks

GEO-PHYSICAL SCIENCE
2011-2012
Mr. Sacks
GEOPHYSICAL SCIENCE
POLICIES & PROCEDURES
Schools exist primarily for the purpose of learning.
To achieve that goal, we both must do our jobs.
I. MY JOB INCLUDES:
1) Arriving to class on time.
2) Being prepared with a clear lesson plan and a thorough knowledge of the
material.
3) Being ready to work when the bell rings.
4) Providing all materials that I’m responsible for.
5) Giving homework and exams which reflect and utilize the concepts presented.
6) Providing current and accurate assessments of your performance.
7) Informing you of short-term assignments and their due dates.
II. YOUR JOB INCLUDES:
1) Arriving to class on time.
2) Being prepared everyday with notebook paper, at least one #2 pencil with eraser,
graph paper (if necessary), colored pencils if needed, and any other materials
accumulated during the course which may be necessary to perform the assigned
work.
3) Being ready to work when the bell rings. This includes being in your designated
seat and starting any warm-up activities.
4) Completing the homework on time and as instructed.
5) Asking questions if you don’t understand something.
6) Taking the necessary steps to legitimately maximize your performance in this
class. Examples would include using effective study techniques, coming in for extra
help when appropriate, doing the homework, taking good notes, taking advantage of
Extra Credit opportunities, etc.
7) Being aware of assignments and their due dates.
8)
PAYING ATTENTION!!
III. DISCIPLINE AND CLASS CONDUCT
No student will be allowed to impede the learning process. It prevents me from
doing my job and the other students from doing theirs. I have found that using the
guideline “impeding the learning process” is a better way to determine what an
offense is than trying to anticipate and list every possible infraction.
ATTENDANCE:
A student is considered tardy if not completely seated at his assigned desk before
the bell stops ringing. Notice how this sharply contrasts with students’ wishful
interpretations like “But I was in the room!”, or “But I was just a little late”, or “But
my books were on the desk. I just had to talk to my girlfriend for a second.” or any
other excuse that starts with the word “But”.
FOOD FOR THOUGHT:
This is a classroom, not a cafeteria, so food doesn’t belong here. It attracts bugs and
rodents, is not consistent with our purpose here, and is unsafe given the fact that
we conduct chemical labs in the room. Water in a plastic container with a screw cap
is welcome. But food (including gum) and other beverages must be consumed
outside the room. Repeat violators will become intimate with that which they love
so well. This love will be demonstrated for one hour after school by sweeping up
crumbs and scraping gum off desks.
IV. GRADING
EXAMS:
There are quizzes (50 pts.), tests (100 pts.), and a cumulative Semester Final Exam
which is worth 30% of the class grade. There are no mid-terms or pop quizzes.
During any exam, you must be entirely self-sufficient during the entire period.
That means no student shall communicate with, nor receive nor supply information
or materials of any kind, from another student - NO EXCEPTIONS! If you have a
question, if you can’t read the board or the exam, if you need to borrow something,
ask me, no one else.
LABS:
These are a good way to apply the stuff we learn, so they will be conducted as often
as equipment and time allow. The point value of labs varies, depending on their
complexity and length.
The lab equipment is safe when used as instructed. However if materials are
abused, then both people and property are put at risk. Necessary safety lectures
will be given before all labs; therefore anyone deliberately endangering persons or
property will be withdrawn from that lab and receive a zero. Continued abuse will
result in expulsion from the course.
There are no plant or animal dissections in this class.
CLASS PARTICIPATION:
Pretty self-explanatory. Ask questions, get involved in the discussions, notice how
the world around you is a giant, living lab. You have the right to learn. You have
the right to remain silent. You also have the right not to learn, assuming that you
want to stay in high school for 7 years and then get a job as a toothpick sharpener.
But one right that you do not have is the prevention of anyone else from learning.
Consequently, actions which impede the learning process are unacceptable, and
responses from the subtle to the severe will result.
HOMEWORK:
“Daily” assignments will generally be the rule (this class does not meet every day).
But I also try to avoid homework on holidays and vacations, and never give an
assignment the day before an exam. At the start of each week, you will be given a
syllabus of the week’s assignments. Each morning, your notes and homework will
be assessed and your progress will be indicated on the syllabus. On the day of the
exam, your syllabus will be collected.
MAKE-UP WORK:
Work missed due to a suspension will not be accepted. Late homework is accepted
only for excused absences. The amount of time you get to make it up is determined
by how long you were out. For example, if you missed 3 school days, then you have
3 school days to make it up. Make-up labs and exams are typically conducted after
school. If that conflicts with your personal schedule (job, medical appointment,
etc.), let me know before that day arrives so that alternate arrangements can be
made. Don’t just go AWOL on the make-up day.
It is to your advantage to take the original exam if possible because repeat tests are
always harder than the original. Consequently, if you know that you’re going to be
gone on an exam day, tell me at least three days in advance so I can let you take the
original one before you leave.
GRADE COMPONENTS:
Exam Grades:
80% - 100% = A
70% - 79% = B
60% - 69% = C
50% - 59% = D
Quarter Grade:
Exams: 50%
Lab Reports: 20%
Homework & Class notes: 30%
Semester Grade:
Quarter 1: 35%
Quarter 2: 35%
Final Exam: 30%
V. LIFE IN GENERAL
You (yes, you) are the paramount factor in how well you do in this class (or any
other class for that matter). You are responsible for your own actions and their
consequences (which includes grades). If you get behind in the work, if you don’t
understand something, if you need some extra help, you have to let me know. (If I
could read minds, I’d be at a poker table right now.) By implementing these
guidelines, I’ll be able to teach more efficiently and you might even find this class to
be interesting (imagine that!)
Mr. Peter Sacks
Science Department
IRVINE HIGH SCHOOL
4321 Walnut Avenue
Irvine, CA 92604 
(949) 936-7000 ext. 7074 
[email protected] 
We understand and accept these policies and procedures.
___________________________
Signature of Student
___________________________
___________________________
Signatures of Parents
THE DO’S & DON’TS OF SCIENCE HOMEWORK
There are two main reasons for doing homework:
1) to reinforce ideas introduced in class
2) to learn additional information or details that are not covered in class.
There is no partial credit on homework - either it’s correctly done, or it’s not.
To get credit for homework, it must be completed on time.
“On time” means that it is ready to be examined on the next school day at
the beginning of the period.
“Completed” means that every answer must convey a self-explanatory idea.
For example, these are not acceptable homework answers:
He died in 1955.
hydrogen
a string of volcanic islands
It has two moons.
These are acceptable answers:
Albert Einstein died in 1955.
Hydrogen is the lightest element.
Hawaii is a string of volcanic islands.
Mars has two moons.
If students have trouble formulating a sufficiently whole response, they may
write the question first, then add their attenuated replies.
The entire assignment must be written correctly for a student to receive any
credit for it. I urge parents to read their child’s homework, not to check for
scientific accuracy, but for clarity of thought, appropriate penmanship, and
proper spelling. (Stew dents dew knot real eyes that Spellcheck dozen Noah
they’re write ants her is.)
Additionally, it’s my belief that learning should be shared.
We acknowledge and understand this.
STUDENT’S SIGNATURE
PARENT’(S) SIGNATURE(S)
MASS VS. WEIGHT
MASS MEASURES HOW MUCH _____________ CONTAINS,
BUT NOT HOW BIG IT IS. (“HOW BIG” = “_________”.
THIS PILLOW IS BIG, BUT IT DOESN’T WEIGH MUCH.)
IN THE METRIC SYSTEM (THE ONE SCIENTISTS AND MOST OF THE WORLD
USES),_________________________________.
WRITE THE MASS OF EACH OBJECT BELOW ITS PHOTO.
“WEIGHT” IS A MEASURE OF _________________________________________.
IT CAN BE WEAK (LIKE ON MARS) OR STRONG (LIKE ON JUPITER) OR ZERO
(LIKE IN OUTER SPACE.)
IT’S MEASURED IN __________ (IN THE ENGLISH SYSTEM) AND IN
______________ (IN THE METRIC SYSTEM).
TYPICALLY A SPRING IS INVOLVED (EVEN IF YOU CAN’T SEE IT.) THAT’S WHY
THE MEASURING DEVICE IS CALLED A _________________ .
NOW WE KNOW WHAT MASS AND WEIGHT ARE, HOW THEY’RE MEASURED, AND
IN WHAT UNITS. BUT HOW ARE THEY DIFFERENT?
MASS VS. WEIGHT
THE BOY’S BODY IS THE SAME ON THE EARTH
AND MOON, SO HIS ____ REMAINS THE SAME.
THE GRAVITY PULLING ON HIM DID CHANGE,
THEREFORE HIS ________ CHANGED TOO.
2.2 LBS
1 KG
0.83 LBS
1 KG
0.37 LBS
1 KG
0 LBS
1 KG
WE’RE NOT GOING TO WEIGH OURSELVES ON THE MOON, SO WHY SHOULD WE
CARE ABOUT GRAVITY?
NAME 2 MORE SPORTS AND HOW
THEY’RE AFFECTED BY GRAVITY.
READING A SCALE PROPERLY
How important is precision? It depends what your motivation is. If you simply want to
convey an idea, then saying “I paid around $300 for my snowboard.” is good enough.
House prices are only accurate to the level of $10,000. (Look at house listings. Prices
are in the form of $270,000. You don’t see them listed as $265,427.42 But gasoline
prices are actually listed to the 1/10 cent. (e.g. $3.229/gallon).
When reporting data, always give one level of precision more than
the smallest unit indicated on the device. One level of precision
more than a dollar would be a dime ($0.10). One level of
precision more than a dime would be a cent ($0.01).
For example, this graduated cylinder’s most precise line indicates
1 milliliter. So the volume read on here should be reported to the
nearest 0.1 ml (like 65.3 ml).
Each minor line on this water
pressure gauge is 0.1 psi, so you
can report its reading to the 0.01
psi (for example 10.47 psi).
This clock has a line for every minute. So it’s more precise than this one
These backyard thermometers may be
pretty to look at, but they’re hard to read
with precision. The temperatures go up
by units of 10, so the best reading you’ll
get is a unit of 1.
What do you think the temperature
reading on this flowery thermometer is?
What’s the reading on this sunny one?
The major lines on this grocery
store produce scale indicate 1 kg.
How much does each minor line
represent?
What is the level of
precision that can be legitimately
read on this scale?
To what level of precision can this leaf be measured on this metric ruler?
Accurately measure it and write the answer here:
To what level of precision can this leaf be measured on this metric ruler?
Accurately measure it and write the answer here:
MENISCUS
3. ______________________
3. ___________________________
Name:
Date:
Class:
Laboratory Techniques Activity #10
Calculating the Surface Area and Volume of a Box
The surface area is the part of the box that has
the information is printed on it (e.g. the name
of the cereal, nutritional information, etc.)
The total surface area is the sum of all 6 sides.
The volume measures how much material the
box can hold.
The sides of a box are rectangles, and the area
of a rectangle is length x width. Assume the
front of the box is 30cm tall and 22cm across.
The side label (see the bar code at the
bottom?) is also 30cm tall but only 8cm across.
The surface area of the front panel is (30cm) x (22cm) = 660 cm cm
(Remember the units undergo the same mathematical process that the
numbers do.) But “cm cm” is written instead as “cm2” or “square cm”.
Note that the back panel will have the same area as the front.
What is the surface area of the left side?
What is the surface area of the bottom of the box?
What is the total surface area of the box?
Volume is actually easier to calculate. Pick
any corner on the box. I just randomly picked
the corner indicated, but ANY corner is OK.
Note that there are 3 edges touching it.
Measure how long they are and then multiply
them together.
Volume = (30cm) x (22cm) x (8cm) =
5280 cm cm cm = 5280 cm3 = 5280 cubic cm.
Continuing our breakfast theme, consider a stick of butter which is
11cm long with a square end meauring 4.5cm on each edge.
What is its total surface area?
What is its volume?
MOTION
Fast
and getting faster
or slower!
Movement is all around us, from electrons to planets, so it’s an
idea that scientists want to understand.
Describe 3 more situations that illustrate something in motion:
1)
2)
3)
How quickly something is moving is
called its _________. (What kind of
ticket do you get for driving too fast?)
Make up an answer: How fast was the
car going?
You probably used “miles per hour” as
the units. (It’s OK if you didn’t.)
What does “miles” measure?
What does “hour” measure?
What does “per” mean?
Making this more generalized, we can deduce
that the equation for speed (or velocity) is:
What could be some other units for speed?
Do the sample math problems here:
What if the speed of something keeps changing?
The roller coaster car is going to ________________.
ANY change in an object’s __________ counts as acceleration.
Is this baseball
player accelerating?
Explain why.
What about
this one?
Explain why.
Three
players walk
off the field
at the end of
the game.
Are they
accelerating?
Explain why.
How can acceleration be calculated?
It’s based on how much the speed changed and how quickly the
change occurred.
The formula is:
If a car goes from 20 mph to 60 mph in 8 sec, what is its
acceleration? Show your work here:
Then the car cruises along at that speed (60 mph) for 10 sec.
What is its acceleration?
Seeing a red light ahead, the driver slows down from 60 mph to
45 mph in 5 sec. What is the car’s acceleration?
A chart or a graph is a common way to depict an object’s motion.
Luke Skywalker is riding in his landspeeder across the Tatooine desert.
The data chart shows how far he was from his home at different times.
Time
(minutes)
10:00
10:05
10:08
10:11
10:25
10:30
Distance
(Km)
)
0
10
15
23
47
62
This same information can be represented on a graph:
Start with a 0 in the lower left corner. (Will it be zero for all graphs?)
Label the vertical axis as “Dist. (Km)” and make each heavy line (not
the minor lines) worth 10Km. Label the horizontal axis “Time (min)”
and make each heavy line worth 2 minutes.
What is the slant of the connecting graph line called?
What is the equation to
calculate the slope of a line?
Draw a small “x” on the two spots of the slope that you’re going
to use for the calculation. Don’t use data points as your 2 spots.
Write the Y-values (the vertical numbers) here:
Starting Y-value =
Did Y get bigger or smaller?
Ending Y-value =
By how much?
Do the same thing for the X-values for the two spots you chose.
Starting X-value =
Did X get bigger or smaller?
Ending X-value =
By how much?
The slope of this graph is distance/time. What does that equal?
Now calculate it. Remember to use the proper units.
Thus, Luke’s landspeeder was going __________.
Similarly, you can get the acceleration of an object if you have a
graph with speed and time on it by calculating its slope.
This graph depicts the motion of the roller coaster car on page 3
as it goes from point Y to point Z.
Why doesn’t the slope line start at 0?
How fast was the car moving at point Y?
How would the graph of the car’s speed be different if the data
showed its motion from point W to point X?
Using the slope of the line, calculate the car’s acceleration.
What did you get? Remember to use the proper units.
CART & RAMP EXPERIMENT
Galileo was very interested in studying gravity and the motion of free-falling objects.
But gravity is fast and equipment during Galileo’s time (1564 – 1642) was slow (no
stopwatches.) So he cleverly thought of using ramps to study the effects of the earth’s
gravitational field, but slowed down. Likewise, we will use ramps to aid in our study.
Each lab group will be analyzing a different configuration of the experiment. The ramp
will be propped up on one end. Note that the wooden blocks are even with the edge of the
track. Some groups will use 1 block, some will use 2, but all will be aligned as shown.
QUESTION #1: Why is it important for all groups to follow this alignment rule?
The purpose of this experiment is to determine what effect the angle of the ramp and the
weight of the car have on the car’s acceleration down the ramp. To alter the weight, 1 or 2
bars of steel will be placed in the cargo area of the cart like this:
Recall that to calculate acceleration, you need two speeds and the time it took to get from
one speed to the other.
You’ll use a stopwatch to time how long it takes to go from the top to the bottom of the
ramp.
Since the cart is being released, its initial speed is zero. How will the final speed be
determined?
The steel bars serve an additional function. They break the beam of light in an electronic
timing gate. This beam was broken for 0.264 seconds. Using the yellow ruler affixed to
the track, measure the length of the steel bar. Convert it from cm to m and then write that
number here:
Be sure that the beam is being broken by the steel bar (whose length you know) and not by
the whole cart (whose length you don’t know). You can tell when the beam is being
blocked because a red light on top of the timing gate will go on (see arrow).
Here’s a close-up of the interior of the timing gate. (You can see the red light on top). The
small hole at the bottom is where the beam of light comes out. The arrow is pointing to it.
You can’t see the beam because it’s infra-red (just light the signal that goes from your
remote to the TV.) That’s why you need to use the red indicator light to verify the correct
alignment of the bar with the timing gate.
Be sure that the steel bar isn’t still blocking the beam after the car hits the bumper at the
end of the track.
After everything’s set up, take the cart to the top of the ramp so its back end is also aligned
with the edge of the track. Push the red “Reset” button on the timing gate.
QUESTION #2: Why is it important that all groups release their carts from the same
point?
Release the cart and use the stopwatch to time how long it takes the cart to reach the
bottom of the track. Record that number here:
Since speed = distance / time, you can calculate the speed of the car upon impact because
you have the distance (the length of the steel bar) and the time (from the electronic display
on the timing gate.)
Now use that final speed and the initial speed (which is 0) and the duration time (from the
stopwatch) to calculate the cart’s acceleration. Do three runs and use the average data for
your calculations. Write that number in the correct box on this chart and up on the
whiteboard so other groups can copy your number (and copy theirs on your chart below).
Circle the acceleration from your lab group (on this page, not the whiteboard).
CART ACCELERATION (m/sec2)
light cart (1 steel bar)
heavy cart (2 steel bars)
low angle
high angle
Conclusions and analysis:
How did changing the angle of the ramp affect the cart’s acceleration?
Explain this conclusion.
How did changing the weight of the cart affect the cart’s acceleration?
Explain this conclusion.
Date & period the experiment was conducted:
Names of all the people in your group:
NEWTON’S LAWS
Sometimes you want to know how fast an
object is moving (called its “_____ ___”)
Sometimes you care how fast
AND what direction it’s moving
in (called “___
____”).
Although “speed” and “velocity” are often used
interchangeably, they’re not exactly the same thing
because velocity includes _______ and speed doesn’t.
For example, “30 mph heading west” is a _______.
“30 mph” is a ______.
Data that include a direction (like “force”)
are called ________ quantities. Those
that don’t (like “volume”) are called
________ quantities.
Additional scalar quantities:
Additional vector quantities:
Like speed & velocity, mass & weight are also similar but not
identical. Mass is a measure of how much ___
___ makes up
a material. Weight measures how strongly a ___________ field
pulls on that material. An object will always have _ ___ _, but
it might not have any ________.
Where would an object have to be if it were weightless?
Of mass and weight, which is a scalar and which is a vector?
Gravitational fields cause mass (i.e. objects) to have weight.
No gravity = no weight.
Since gravity is all around us, we’d better know about it.
Different planets have different gravity field
strengths. Earth’s causes objects to accelerate
at about 10 m/sec/sec. On the moon, it’s
about 1.64 m/sec/sec. Mars is 3.73 m/sec2
and Jupiter’s gravity is 26 m/sec2! But on that
planet (or moon) it’s the same for ALL objects.
To quote Yoda, “Size matters ____”. If air
friction is not significant, all objects will fall at
the same rate. The reason why this is true will
be explained later. But crazy Mr. Sacks will
prove it now!
Calculations with gravity (but first, a quick math review):
Write the equation for calculating
the speed of an object:
Write the equation for calculating
the acceleration of an object:
Recall the archer on the first page. If he realeases the string and
the arrow reaches a speed of 54 m/sec in 0.09 seconds, what was
its acceleration?
It continues at that speed (54 m/sec) flying across a field toward
its target, which gets hit 2 seconds later. How far away was the
target?
The target stops the arrow in 0.60 seconds. What was the
resultant acceleration of the arrow?
By definition, a free-fall is one in
which air friction is so small that it
can be ignored (typically because
the object is falling for a short
distance, or because of its size or
shape.) A boulder will readily freefall. A snowflake? Not even close!
If an Olympian on a 3m high dive
hits the water after free-falling for
¾ second, how fast will he be going
when he makes a splash?
Note that an object will
lose speed on the way up
just as quickly as it is
gained on the way down.
That’s why the path of a
fly ball hit into the
outfield or a pendulum is
symmetrical.
If a ball of pyrotechnic material is fired
upward (like at a fireworks display), it will
lose speed at the rate of -10 m/sec for every
second it ascends, until it finally stops at its
peak (called the “apex”).
If a ball is shot up at 70 m/sec, how fast will
it be going after 1 sec?
How fast after 2 sec?
After 5 sec?
How long will it take to reach its apex?
Now we can learn about a scientist
who taught us a lot about movement:
Galileo Galilei (1564 – 1642).
Coincidently, he was born the same
year as the famous British playwright
shown here. Who is he?
Galileo introduced the idea of “inertia”, from a word meaning
“non-changing”. The non-changing aspect of matter is its
motion. The more mass an object has, the harder it is to change
its motion.
Compare an empty shopping cart to one
heavily loaded up like this one. Which
would be harder to start moving?
Which one (heavy or light) would be
easier to keep going once it’s already
moving?
Which would be harder to turn?
More mass means more inertia – more resistance to change in
motion. That means ANY change in motion – speeding up or
slowing down or turning.
What’s a scientific synonym for “motion”?
What previously-introduced term means the same as “a change in
motion”?
Hunters often use heavier bullets because they tend to keep on
going, fighting against air friction, better than lighter bullets can.
What’s the advantage of using a light tennis racket?
What’s the disadvantage?
NEWTON’S FIRST LAW:
AN EXTERIOR FORCE APPLIED TO AN OBJECT WILL CHANGE
THAT OBJECT’S MOTION.
(IF MULTIPLE FORCES ARE BEING APPLIED, THEN THE
RESULTANT FORCE WILL CHANGE THE MOTION.)
NEWTON’S SECOND LAW:
THE FIRST LAW SAYS: IF YOU PUSH ON AN OBJECT, ITS
MOTION WILL CHANGE. THE SECOND LAW CALCULATES HOW
MUCH IT WILL CHANGE. THAT AMOUNT DEPENDS ON HOW
HARD YOU FORCE AND HOW HARD THE OBJECT CAN RESIST
THE CHANGE.
WHAT PHYSICS TERM IS SYNONYMOUS WITH “MOTION”?
WHAT IS A SYNONYM FOR “CHANGE IN VELOCITY”?
WHAT PROPERTY OF MATTER MAKES IT RESISTANT TO
ACCELERATION?
WHICH BALL HAS MORE INERTIA?
WHY?
INERTIA IS AN IMPORTANT FACTOR, BUT IT CAN’T BE
MEASURED. WHAT IS IT RELATED TO THAT CAN BE
MEASURED?
ALL THESE IDEAS COME TOGETHER IN NEWTON’S 2ND LAW:
F=ma
NOTE THAT F & a ARE IN BOLD FONT, INDICATING THEY’RE
VECTOR QUANTITIES AND m IS IN STANDARD FONT BECAUSE
IT’S A SCALAR QUANTITY.
WHAT’S THE DIFFERENCE BETWEEN A SCALAR AND A VECTOR
QUANTITY?
UNITS FOR THE EQUATION:
ENGLISH:
F=m a

METRIC:
IT TAKES 20N OF FORCE TO ACCELERATE A 10kg
BOWLING BALL BY 2 m/sec2.
HOW MUCH FORCE WOULD IT TAKE
TO ACCELERATE A 500g BASEBALL
BY 30 m/sec2?
“WEIGHT” IS A COMMONLY ENCOUNTERED FORCE, CAUSED BY
GRAVITATIONAL FIELDS. SO YOU CAN CALCULATE A WEIGHT
USING A SPECIFIC FORM OF NEWTON’S SECOND LAW:
w=m

g
“g” IS THE SAME 10 m/sec2 THAT WE STUDIED BEFORE.
THUS, A 5KG BIKE WEIGHS 50N ON EARTH.
ON JUPITER, g = 26 m/sec2, SO THE SAME
BIKE WOULD WEIGH 130N.
ONE POUND WEIGHS ABOUT 4 NEWTONS
(ON EARTH). SO A QUARTER-POUNDER IS
ALSO A NEWTON-BURGER!
The exploding gunpowder in a cannon
applies 6000N of force to the 4kg cannonball
inside it. What will be the ball’s resultant
acceleration?
A woman throws a Frisbee for her dog to
catch. If she exerts 5N of force on the 200g
disc, how much will it accelerate?
A dummy hangs from a tree, part of a Halloween display.
If the dummy’s mass is 30kg, how much does it weigh?
How much tension is in the rope?
Is the dummy in static equilibrium or dynamic equilibrium?
How do you know?
A 400g football is thrown to a teammate at 6 m/sec.
He catches the ball, stopping it in 0.2 seconds. How
much force did he exert on it?
Why is the force negative?
Lois Lane has fallen from the roof of The Daily
Planet. Superman flies down to save her before
she splats onto the sidewalk below. Her mass is
50kg. If the net force on her is 150N upward,
what will be her resultant acceleration?
If she was moving 12 m/sec when he caught her,
how many seconds will it take him to slow her
down and stop her?
Going from “Y” to “Z”, a roller coaster
car has a resultant force of 2000N
acting on it (pulling it down the hill).
The mass of the car and the
passengers totals 1000kg.
If the car is going 7 m/sec at point Y,
how fast will it be going when it
reaches the bottom of the hill three
seconds later?
Medieval physics!
A catapult team loads a
100kg rock into their
weapon. To reach the
enemy’s castle, the rock
must be going 30 m/sec
when it’s launched. But
it’s in the bucket for only
1½ seconds before it
flies out.
How much force will the catapult need to supply to accomplish this?
Bart uses his slingshot to launch a 70g rock with a force of 20N.
If the launch takes 1/5 second, how fast will the rock be sailing
through the air?
Friction is a commonly-encountered factor in your life.
Sometimes you want to maximize it
and sometimes you want to minimize it.
Sometimes you want both.
List 2 more examples of helpful friction:
1)
2)
List 2 more examples of unhelpful friction:
1)
2)
Friction alters an object’s motion (whether you want it to or not!)
In Physics, “motion” means _________.
“altering an object’s velocity” means the same as ____________.
According to Newton’s Second Law, what accelerates an object?
Therefore, FRICTION IS A TYPE OF FORCE!
Just like apples, bananas, and grapes are all classified as “fruits”, so are
friction
tension
weight
and buoyancy
all examples of forces (there are others.)
Since friction is a force, what would its units be?
The amount of frictional force between two objects depends on:
a) what the materials are (e.g. metal skates on the ice)
b) how hard they’re pushed against each other.
When you play duck-duckgoose, how is friction a
necessary part of the game?
Friction between the tires and the road
give this car 1000 N of propellant force.
If the car’s mass is 800kg, what will be
its acceleration?
How long will it take the car to reach 25 m/sec?
A runner slides into 3rd base,
incurring 75 N of frictional force.
His mass is 50kg. What will his
acceleration be?
If he hit the ground going 3 m/sec,
how long will it take him to stop?
Can friction co-exist with other forces? Yes!
Newton’s Third Law
Newton’s First Law states that an object will maintain its velocity
(whether it’s moving or not!) if there’s no net force acting on it.
Newton’s Second Law says that if you decide that you DO want to
change an object’s motion, the net force you’ll need to apply to that
object depends on how hard it can fight against the force you’re
applying (derived from its mass) and how quickly you want to change
its motion (acceleration). In equation form, F = ma
Newton’s Third Law says that the object will push back on you just
as hard as you push on it.
Kick a soccer ball.
Sounds like fun!
Kick a bowling ball. Ouch!
Why?
Kick a football. Go Irvine!
Shooting a BB gun or a dart gun - not much kick.
Firing artillery – A LOT OF KICK!
But guns, even big guns, fired in the movies never kick. Why?
(This is Indy shooting the swordsman in “Raiders
of the Lost
Ark”)
Don’t forget about the Second Law!
The cue ball (white) exerts
a force on the 8-ball
(black). So the black ball
will accelerate. The black
ball exerts the same
amount of force back on the
white, so the white ball’s
motion changes too.
How does this photo of 2 rams butting heads against each other
illustrate each of Newton’s Laws?
I)
II)
III)
Figuring it out:
The target shooter
fires a 2kg gun which
will launch 50g of
lead at the flying clay
disc. If the bullet
accelerates out at
1000 m/sec2, what
will be the resultant
kick (acceleration) of
the gun?
Look sharp
maties!
Thar be
pirates
about!
Cannons on ships are anchored to the walls by ropes. Why is that
necessary?
Note that the rope is loose before the cannon is fired (left photo) and
tight after it’s been fired (right illustration). How did the rope get
tight?
Why not keep it tight from the beginning? Why must it start off loose?
A 400kg cannon will fire a 5kg cannonball. But if the cannon kicks
back faster than 8 m/sec2, its ropes will break the anchor bolts.
What’s the greatest acceleration that the cannonball can have without
exceeding the safety limit on the ropes? Give this problem a shot!
(Hyarrr – Captain Sacks made a humorous quip, he did!)
An octopus doesn’t have
fins like fish do. How can
it swim through the water?
One last cannon conundrum:
The acceleration of this 600kg cannon must be limited to 30 m/sec2
(or it will get too off-target for the second shot.) The amount of
gunpowder loaded into it will ensure that requirement is met. The
explosion lasts 0.02 seconds. How fast will an 8kg cannon ball fly out?
A boy hits a piñata with 40N of force,
causing the piñata to swing away. If
the piñata’s mass is 5kg, how quickly
will it accelerate away?
If the boy’s broomstick has a mass of
2kg, what will its acceleration be
upon impact?
The player with the ball
(#35) knocks his
opponent (#12) off his
feet. The airborne #12
has a mass of 100kg.
He was running 6 m/sec
but #35’s hit stopped
him in 0.4 seconds.
How much force did
#35 exert against #12?
How much force did #12 exert back on #35?
What effect does #12’s force against #35 have against the latter?
If #35 has a mass of 125kg and was running 5 m/sec before the
impact, how fast was he running after the hit?
In this illustration, which player is getting hit harder?
INTRODUCTION TO WAVES
Waves are all around us, even some you can’t see or feel.
Give 2 examples of waves you can detect, and 2 you can’t.
1)
1)
2)
2)
What is a wave?
Waves transmit energy, not matter.
Waves can be categorized in several ways:
1) How they’re grouped
Specular
Diffuse
2) How they travel
Some waves must move through a material (like earthquakes). Some
can pass across a vacuum (like light).
3) How they’re generated
Forward & backward (called longitudinal) or side-to-side (called
transverse).
The material (if any) that a waves passes through is called its
transmission medium.
For an earthquake, it’s the ground. For music, it’s the air. Some
waves, like light and heat, can travel through the emptiness of outer
space. They’re called energy waves. Those that must travel through
a substance, like sound or oceanic, are called matter waves. Most
energy waves are transverse and most matter waves are longitudinal.
When a crowd “does the wave”, is it a longitudinal or transverse wave?
Matter or Energy wave?
Note that the wave travels for 100’s of meters, but the people don’t.
The energy is being transmitted, not the matter.
Everything has parts. You learned that as a kid.
(“Where’s your nose?” “Where’s your tummy?”)
Waves have parts too.
Crest – the highest measured value of the wave (e.g. highest voltage,
brightest light, greatest pressure, etc.)
Trough – shaped like the feed box, it’s the opposite of the crest.
Wavelength – how long the wave is! (measured between 2 comparable
points, like from one trough to the next). Symbol is  (Greek lambda)
Frequency – how frequently the wave is produced (2 times per second,
5 times per week, etc.) Symbol is f.
Amplitude – the maximum distance from equilibrium. Symbol is A.
“waves/sec” is such a common
unit for frequency, that it has a
shortened,
eponymous unit
called “Hertz”
(abbreviated Hz).
So 47 Hz =
47 waves/sec.
The AM radio band
is kHz and FM is MHz (“M”
means “mega” which = million).
The frequency of the radio wave
that broadcasts 102.7 KIIS-FM
is 102,700,000 Hz!
speed = frequency x wavelength
Waves travel at different speeds (the speed of light is about a million
times faster than the speed of sound!) The speed is determined by the
transmission medium. For example, a particular slinky will produce a
specific speed. Shaking the slinky faster makes the frequency greater,
but the wavelengths will also get smaller, so the two effects cancel out
and you’re still left with the same final speed.
Momma duck has a long stride (compared to the babies) but she moves
her legs infrequently. The chicks have a short wavelength (the distance
from one footprint to the next is small), but they move their legs
frequently. This way all the birds have the same speed!
MAJOR GROUPS OF WAVES
The colors of light that we can see are a small part of a larger set of
waves called the electromagnetic spectrum.
All the waves in it are transverse energy waves.
All sound and shock waves are longitudinal matter waves.
Oceanic waves are a hybrid of transverse + longitudinal.
There are 6 types of earthquake waves. Some types are transverse,
some are longitudinal, and some are hybrids. And some you won’t
learn about until college!
DOPPLER SHIFT
DISCOVERED BY CHRISTIAN JOHANN DOPPLER,
IT EXPLAINS THE DIFFERENCE BETWEEN THE
TRUE AND PERCEIVED FREQUENCY WHEN AN
OBJECT AND OBSERVER ARE MOVING RELATIVE
TO EACH OTHER.
ANY WAVE CAN BE SHIFTED, BUT THE SPEED OF THE MOVER MUST BE
SIGNIFICANT COMPARED TO THE SPEED OF THE WAVE; SO SOUND
WAVES ARE MORE COMMONLY SHIFTED THAN LIGHT WAVES.
When an earthquake occurs,
the moving crustal plates can
change the frequencies of the
waves coming from the origin
of the disturbance.
Waves interact with their environment.
Every time a wave enters a new material
(i.e. transmission medium), some of its
energy will bounce off and some will continue
on. The part that bounces off the boundary
surface is called the reflected wave. It turns out that the incoming
wave (called the incident wave) enters at the same angle that the
reflected wave bounces off.
Anyone who’s played air
hockey or pool has noticed
this. When a wave enters a
new transmission medium,
its speed changes, which
causes it to bend. This
bending is called refraction.
It’s how things like
magnifying glasses work.
This dual property of reflection and transmission is especially noticeable
in glass.
This phenomenon is called
“Pepper’s Ghost” after Sir Henry
Pepper (1821-1900).
He used it to make
the first believable
ghost illusion on
stage (“Hamlet”
shown above and
“A Christmas Carol”
(in 1862!) below.)
The Haunted Mansion also uses the effect.
You’re on one side of the glass and the “hitchhiking ghosts” are on the
other. The lights on your side illuminate you, then bounce off and go to
the glass, then reflect again to your eye so you see yourself in the
glass. Light on the ghosts’ side bounces off them and transmits
through the glass to you!
The grand ballroom is the largest “Pepper’s Ghost” in North America!
The changing paintings in hallway are a transmission illusion. Two
projectors shine onto the back of a blank canvas. You see only the
transmitted light. One projector shows the normal image and the other
shows the haunted image. As they take turns shining, the “painting”
appears to be changing.
Madame Leota in the séance room, and the singing busts in the
graveyard are clever exploitations of reflection. They’re basically 3-D
movies screens. When a movie of someone singing is projected onto it,
the blank white head appears to be actually singing.
Waves can also interfere with each other. An incoming wave
approaching a beach will interfere with the retreating wave that
preceded it. All the radio waves from different stations (KIIS-FM,
POWER 106, etc.) are interfering with each other right now. The light
waves of the different colors coming from your clothes are interfering.
If the two interfering waves have different amplitudes from each other,
you will get partial (instead of complete) constructive or destructive
interference. But the effect is the same. For example, in (b) above, if
the upper wave has an amplitude of +7 volts and the lower has an
amplitude of -3 volts, then their resultant would be +4 volts.
SOUND WAVES
Sound waves are
longitudinal / transverse
matter / energy
waves.
Circle the correct answer.
Circle the correct answer.
They can reflect.
Sonar and Radar are examples of this. What is a reflected wave called?
(Hint: the answer is both a noun and a verb.)
Geologists use reflection to
determine how thick a layer of
rock is.
An explosive charge is
detonated, and the time it
takes to return (where it’s
picked up by microphones)
and the known speed of the
shock wave are combined to
figure out how far down the
rock boundary is.
If the speed of the wave is 4000 m/sec and the time between the
blast and the echo is 25 milliseconds, how deep is the rock layer?
A hungry dolphin is swimming after
its breakfast. The speed of sound in
water is 1500 m/sec. The dolphin
stops and sends out a burst of waves
which return in 0.1 seconds.
How far away is the fish?
3 seconds later, it sends out another pulse which returns in 0.4 sec.
How far away is the fish then?
What is the speed of the fish? Is it moving toward or away from the
dolphin? How do you know?
Look at the green handout that lists the speed of sound in different
materials. What three basic categories have the substances been
broken into?
What general conclusions can you make between the speed of sound
through a material and what state of matter that material is?
The speed of sound in air get faster as the air gets hotter. Why?
The speed of sound in the positive temperature range can be
calculated by this equation:
speed = 331.5 m/sec + (0.6 m/sec/oC) (temperature of the air)
Write your practice problems below:
As we learned before, when a wave hits a new material, some of
that wave will bounce back. And that returning wave can interfere
with a subsequent incoming wave. This results in constructive and
destructive interference (either partially or completely). Points of
complete destructive interference are called nodes (like NO motion.)
Points of completely constructive interference are called antinodes.
When you’re jumping rope, your body is
inside an antinode! What would your hands
represent?
When this type of wave interference
pattern occurs, you don’t see a single
pulse going from end to end anymore
(those are called traveling waves).
And instead what you get are wave
patterns that just look like they’re
flopping up and down (like the jump
rope). So they’re called standing
waves. Musical notes are all
standing waves (produced by strings,
air in a pipe, a drum head, etc.)
The frequency that something
naturally vibrates at is called its
natural or fundamental frequency.
When a string is plucked in the middle,
it will vibrate at its natural frequency,
also known as the First Harmonic
(shown here as N= 1). It is the lowest
frequency that can sustain a standing
wave. That string can also vibrate at
twice its fundamental frequency, called
the Second Harmonic (N = 2).
If the First Harmonic is 70 Hz, what is
the frequency of the Second Harmonic?
What is the frequency of the 4th Harmonic (N = 4)?
Sound waves also refract. How much they bend, and in what direction,
help us identify the different layers of the earth’s crust and interior.
You can’t see around a
doorway, but you can hear
sounds around it. What wave
phenomenon does this
illustrate?
When the cameraman yells
“Action!”, the actor inside can
hear him, but not see him.
Why?
The Inverse Square Law
As a wave travels farther from its source, it seems to get weaker. Actually, total energy
remains constant, but it gets spread out over an increasingly larger area. So its energy per
square foot is reduced.
As you get 4 times farther away, the energy is 4 squared or 42 = 4 x 4 = 16 times weaker.
Five times farther away would show the energy per square foot is 25 times weaker.
What would the energy be at 7 times the original distance?
Sonic boom!
Alexander Graham Bell
(1847 – 1922)
The unit for loudness is the Bel (named for Alexander Graham Bell), but
we actually use only the decibel. These are decibel intensity levels of
several sounds. Remember that both the loudness AND duration of a
sound affect hearing loss.
RESONANCE: CAUSING AN
OBJECT TO VIBRATE AT ITS
NATURAL FREQUENCY (OR A
WHOLE-NUMBER MULTIPLE
OF THAT FREQUENCY) BY
SUBJECTING IT TO WAVES
OF THAT FREQUENCY. THE
INDUCED WAVE IS CALLED A
SYMPATHETIC VIBRATION.
LIGHT NOTES
INTRODUCTION TO COLOR
ALL CULTURES AND ALL RELIGIONS HAVE SOME
EXPLANATION OF WHERE THE UNIVERSE STARTED.
AND IT ALMOST ALWAYS INVOLVES LIGHT. SUN
GODS ARE PROMINENT IN ALL POLYTHEISTIC
RELIGIONS. (WHO IS THE EGYPTIAN SUN GOD
SHOWN HERE?)
EVEN THE ATHEISTIC
SCIENTIFIC EXPLANATION
INVOLVES LIGHT.
WHAT’S THIS THEORY
CALLED?
WHY ARE BANANAS YELLOW AND CHERRIES RED AND BLUEBERRIES BLUE
BUT ZEBRAS AND PANDAS AND POLAR BEARS AREN’T COLORED AT ALL?
WHAT GIVES GOLD, SILVER, AND COPPER COLORS SO DISTINCTIVE THAT
THEY’RE NAMED FOR THE METALS THEMSELVES?
WHETHER IT’S COLORED OR NOT, EVERYTHING IS MADE OF ATOMS. AN
ATOM OF GOLD IS DISTINCT AND DIFFERENT FROM AN ATOM OF
ALUMINUM.
HOW?
A PARTICLE OF LIGHT IS CALLED A PHOTON (LIKE THE PHOTON
TORPEDOES ON “STAR TREK”.)
WHAT ART FORM GETS ITS NAME FROM THIS DEFINITION?
A COLOR IS JUST A PARTICULAR FREQUENCY OF ENERGY THAT A PART OF
OUR BODY CAN PERCEIVE (LIKE SOUND WAVES).
THE ATOMS IN A CHERRY HAVE A UNIQUE CONFIGURATION THAT ALLOWS
ONLY SMALL ELECTRON JUMPS, THEREBY RESULTING IN A SMALL ENERGY
COLOR (RED). LIKEWISE, A BLUEBERRY DOESN’T TASTE LIKE A CHERRY
BECAUSE IT’S MADE OF DIFFERENT SET OF ATOMS AND MOLECULES. ITS
CONFIGURATION WILL NOT ALLOW SMALL JUMPS, ONLY BIG. THIS
RESULTS IN THEIR HIGH ENERGY COLOR (BLUE).
WHAT SIZE JUMP DO YOU THINK HAPPENS IN GREEN GRAPES? WHY?
LASER PRODUCES A VERY SPECIFIC
FREQUENCY (AND THEREFORE
COLOR). IT’S LIKE A TUNING FORK,
BUT FOR COLOR. THIS IS WHY THEY
CAN BE USED TO REMOVE TATTOOS.
JUST AS SINGING THE RIGHT PITCH
CAN BREAK A WINE GLASS, OPTICAL
RESONANCE CAN DESTROY THE
PIGMENTED CELLS IN A TATTOO.
IF YOU MIX ALL THE COLORS OF LIGHT TOGETHER, YOU GET WHITE LIGHT.
WHY ISN’T THIS TRUE FOR PAINT?
YOU CAN ALSO “RUN IT BACKWARDS” AND SPLIT UP WHITE LIGHT AND SEE ITS
COMPONENT COLORS. THIS PROVES THAT WHITE LIGHT IS THE COMBINATION
OF ALL THE COLORS – IT CONTAINS ALL THE COLORS OF LIGHT. THE SUN’S
WHITE LIGHT PRODUCES ALL THE COLORS OF THE RAINBOW.
THE LEAVES ON THE BLUE-BERRY BUSH
ABSORB ALL THE WHITE’S COLORS,
BUT RE-EMIT ONLY THE GREEN
COMPONENT. WHY?
SIR ISAAC NEWTON USING A PRISM
TO STUDY THE BEHAVIOR OF LIGHT.
TWO LIMOSINES ARE PARKED
OUTSIDE A WEDDING RECEPTION.
SITTING UNDER THE SAME SUN,
WHICH ONE WILL GET HOTTER?
WHY?
LASER + BLACK + WHITE = BAR CODE!
SAMUEL MORSE (1791 – 1872)
RECALL THE RESONANCE EXPERIMENT. IT SHOWED
THAT THE SPEED OF A WAVE DEPENDS ON THE MEDIUM,
NOT THE WAVE.
ELECTROMAGNETIC WAVES (WHICH INCLUDE LIGHT)
TRAVEL FASTEST THROUGH A VACUUM. WHY?
LIGHT WILL TRAVEL FASTER IN HOT AIR THAN IN COLD.
WHY?
ALSO RECALL THAT WHEN ANY
WAVE ENTERS A NEW MEDIUM,
IT WILL BEND (TOWARD THE
NEW MATERIAL IF IT SLOWS
DOWN, AND AWAY FROM THE
NEW MEDIUM IF IT SPEEDS UP.)
WHAT’S THE SCIENTIFIC WORD
FOR THE BENDING OF A WAVE AS
IT ENTERS A DIFFERENT
MEDIUM?
WHEN AIR (OR ANY FLUID) IS HEATED, IT WILL RISE – BUT NOT IN A
STRAIGHT LINE. SO SOME AREAS WILL BE WARMER THAN OTHERS. SO
LIGHT WILL MOVE FASTER IN SOME PLACES THAN OTHERS. AND IT WILL
BEND WHEN IT HITS AN AREA OF A DIFFERENT TEMPERATURE. THAT’S
WHAT CAUSES THE DISTORTION YOU SEE WHEN THE AIR IS HOT.
THIS IS ALSO WHAT CAUSES MIRAGES.
IT TURNS OUT THAT MORE FREQUENCY MEANS MORE BENDING, SO
HIGHER FREQUENCIES REFRACT MORE THAN LOWER ONES DO. THIS
PHENOMENON IS CALLED “DISPERSION”.
WHICH COLOR BENDS THE MOST WHEN IT’S REFRACTED?
RAINBOWS ARE THE
RESULT OF
DISPERSION AND
REFLECTION. (NOTE
THAT RED IS ALWAYS
BENT THE LEAST AND
VIOLET THE MOST.)
REFRACTION, SCATTERING, AND DISPERSION ALSO EXPLAIN WHY THE
SKY IS BLUE AND SUNSETS ARE RED. (DO YOUR HOMEWORK TONIGHT
AND YOU’LL FIND OUT HOW!)
ANOTHER USEFUL EXPLOITATION OF REFRACTION INVOLVES LENSES.
WE’LL STUDY TWO BASIC SHAPES OF LENSES:
CONVERGING (CONVEX)
(Who is this famous
fictional detective?)
AND DIVERGING (CONCAVE).
THINK OF A LENS CENTERED ON A COORDINATE AXIS.
THE X-AXIS IS ALSO CALLED THE PRINCIPLE AXIS. RAYS
OF LIGHT THAT COME IN PARALLEL TO THE X-AXIS WILL
PASS THROUGH A CONVERGING LENS AND ALL HEAD
TOWARD A SINGLE POINT CALLED THE FOCAL POINT.
THE FOCAL LENGTH OF A LENS IS THE DISTANCE FROM
THE ORIGIN TO THAT FOCAL POINT. IT IS LISTED AS A
POSITIVE NUMBER (FOR EXAMPLE +5cm OR +4 INCHES).
FOR A DIVERGING LENS, THE PARALLEL RAYS WILL ALL
POINT AWAY FROM A SINGLE SPOT. IT’S STILL CALLED A
FOCAL POINT, BUT THE FOCAL LENGTH OF A DIVERGING
LENS IS A NEGATIVE NUMBER (LIKE -6cm).
THOSE RAYS DON’T REALLY EMANATE FROM THE FOCAL POINT, SO
THEY’RE SAID TO PRODUCE A VIRTUAL IMAGE. RAYS COMING FROM A
CONVERGING LENS REALLY DO PASS THROUGH THE FOCAL POINT, SO
THEY FORM A REAL IMAGE.
LENSES ALSO HAVE A RADIUS OF CURVATURE. IT’S EQUAL TO THE
RADIUS OF THE CIRCLES WHOSE INTERSECTION HAVE THE SAME SHAPE
AS THE LENS. TODAY YOU’LL LEARN HOW TO DRAW A PROPERLY-SIZED
SYMMETRICAL LENS CENTERED ON ITS COORDINATE AXIS.
LIKE CONVERGING LENSES,
CONVERGING MIRRORS PRODUCE
REAL IMAGES AND REFLECT
PARALLEL RAYS TOWARD A SINGLE
POINT. THEY ARE USED FOR
SATELLITE DISHES AND THE BOWLS
OF FLASHLIGHTS & SEARCHLIGHTS.
JUST LIKE DIVERGING LENSES, DIVERGING
MIRRORS SPREAD OUT THE PARALLEL LIGHT
RAYS THAT HIT IT. THEY ARE USED FOR
SECURITY & SAFETY, LIKE TO SEE AROUND
CORNERS IN HALLWAYS & PARKING
STRUCTURES, IN THE QUICKIE MART, AND THE
SIDE-VIEW MIRRORS OF CARS.
LIGHT WAVES LEAVE A
SOURCE IN MULTIPLE
ORIENTATIONS. A
POLARIZING FILTER CAN
ELIMINATE UNWANTED
ONES.
CERTAIN ORIENTATIONS OF LIGHT WAVES PRODUCE GLARE. POLARIZING
GLASSES (OR FILTER) CAN ELIMINATE THEM SO YOU CAN SEE MORE
CLEARLY.
RECALL THE DIFFRACTION OF WAVES (THEY BEND AS THEY GO THROUGH
A BREAK IN A BOUNDARY). THE AMOUNT OF DIFFRACTION IS
DETERMINED BY HOW CLOSE THE WAVELENGTH IS TO THE LENGTH OF
THE GAP.
THE WAVELENGTH OF LIGHT IS VERY SMALL (COMPARED TO SOUND)
FROM 400nm FOR VIOLET TO 650nm FOR RED. “nm” IS SHORT FOR
“NANOMETER” = “MILLIONTH OF A METER” FOR COMPARISON, YOUR HAIR
IS ABOUT 75nm THICK. SO A VERY SMALL GAP WILL DIFFRACT LIGHT.
ADMITTEDLY, THIS
PHENOMENON BY ITSELF
MAY BE UNIMPRESSIVE,
BUT COMBINED WITH
DISPERSION, IT ALLOWS
SCIENTISTS TO FIGURE
OUT WHAT’S INSIDE
DISTANT STARS,
IDENTIFY UNKNOWN
MATERIAL, DISTINGUISH
FAMOUS ARTWORK FROM
FRAUDS, ETC….
REMEMBER THAT DIFFERENT ELEMENTS WILL
LOOK DIFFERENT (E.G. SILVER VS. GOLD)
BECAUSE OF THEIR ATOMIC CONFIGURATION
(PRIMARILY HOW MANY ELECTRONS IT HAS
AND WHERE THEY JUMP AND FALL WHEN IT’S
ILLUMINATED). LIKE A CHORD IN MUSIC, AN
ILLUMINATED ELEMENT MAY PRODUCE
SEVERAL FREQUENCIES OF LIGHT.
A DIFFRACTION GRATING CAN SPLIT THEM UP,
REVELING THE INDIVIDUAL COLORS UNIQUE
TO THAT ELEMENT.
A VERTICAL BEAM OF WHITE
LIGHT SHINING ON A SCREEN
A VERTICAL BEAM OF WHITE
LIGHT PASSING THROUGH A
DIFFRACTION GRATING, THEN
SHINING ON A SCREEN.
A VERTICAL BEAM OF LIGHT
FROM A COLORED SOURCE
(E.G. A NEON SIGN) PASSING
THROUGH A DIFFRACTION
GRATING, THEN SHINING ON
A SCREEN.
A SPECTROSCOPE USES A DIFFRACTION GRATING TO SPLIT UP LIGHT
COMING FROM A SOURCE SO ITS UNIQUE COMBI-NATION OF COLORS CAN
BE BROKEN DOWN AND COMPARED TO KNOWN STANDARDS FOR
IDENTIFICATION.
IT’S LIKE IDENTIFYING THE INGREDIENTS IN BBQ SAUCE.
LOOK AT HYDROGEN’S SPECTRUM. IF YOU HAVE A MYSTERY LIGHT WHICH CONTAINS
THOSE 4 LINES IN THOSE SAME PLACES, THEN IT CONTAINS HYDROGEN (AND
POSSIBLY OTHER STUFF). DETECTIVES WHO FIND A WEAPON WITH DIFFERENT
FINGERPRINTS ON IT HAVE TO FIGURE OUT WHO HELD IT – THIS IS THE SAME IDEA.
THIS IS NOT A NEW IDEA. SPECTROSCOPES HAVE BEEN AROUND FOR A
LONG TIME. SOME ARE FANCY AND SOME ARE COMPLEX. BUT THEY ALL
WORK OFF THE SAME PRINCIPLE.
ELECTRICITY
THIS POWER SOURCE IS COMMON (AND COMMONLY UNDERSTOOD) TODAY,
BUT OUR KNOWLEDGE OF IT STARTED AROUND THE SAME TIME AS SOUND
WAVES (LIKE CHRISTIAN DOPPLER) AND FORCES (LIKE ISAAC NEWTON) AND
OTHER SCIENTIFIC DISCOVERIES. ONE OF THE MOST FAMOUS EXAMINERS OF
ELECTRICITY IS THAT GUY ON THE $100 BILL.
BEN FRANKLIN THOUGHT LIGHTNING AND
ELECTRICITY WERE THE SAME THING (HE WAS
RIGHT). HE ALSO THOUGHT THAT ELECTRICITY
WAS MADE OF POSITIVE PARTICLES (LIKE
PROTONS) – HE WAS WRONG ABOUT THAT
ONE. ELECTRICITY IS ELECTRONS.
ELECTRICITY IS MADE OF
ELECTRONS MOVING THROUGH A
WIRE. BUT REMEMBER THAT THE
WIRE IS MADE OF ATOMS AND THEY
CONTAIN ELECTRONS TOO. AND ALL
ELECTRONS ARE CREATED EQUAL.
SO WHEN ELECTRONS
(ELECTRICITY) COMES OUT OF A
BATTERY OR A LIGHT SOCKET OR A
WALL OUTLET, THEY MOVE
THROUGH A WIRE THAT ALREADY
CONTAINS ELECTRONS.
IT’S LIKE A PIPE FILLED WITH IDENTICAL MARBLES. EVERY NEW MARBLE
THAT ENTERS THE PIPE WILL SHOVE ALL THE OTHER MARBLES (ELECTRONS)
DOWN THE PIPE AND ONE WILL POP OUT THE OTHER END. HOW HARD THOSE
ELECTRONS ARE FORCED INTO THE WIRE IS CALLED VOLTAGE AND HOW
MANY ARE MOVING IS CALLED THE CURRENT.
THE MARBLE THAT GETS PUSHED OUT
IS BASICALLY A DEAD ELECTRON. IT
STILL EXISTS, BUT IT HAS NO POWER
LEFT. WHEN ALL THE ELECTRONS
HAVE FLOWED FROM ONE END OF
THE BATTERY TO THE OTHER, THE
BATTERY IS DEAD.
ELECTRONS DON’T TRANSFORM INTO LIGHT (OR HEAT OR MOTION, ETC.).
THEIR ELECTRICAL ENERGY IS JUST CONVERTED INTO SOME OTHER KIND OF
ENERGY (KINETIC, ACOUSTIC, THERMAL, ETC.) THE FALLING WATER SHOWN
HERE DOES WORK ON THE PADDLE WHEEL SO IT CAN SPIN (AND THEN THE
WHEEL CAN GRIND GRAIN OR MAKE THE BORES OF CANNON BARRELS, ETC.)
THE WATER AT THE BOTTOM OF THE WHEEL STILL EXISTS, BUT ITS
GRAVITATIONAL ENERGY HAS BEEN CONVERTED TO SOMETHING ELSE (THE
WHEEL’S KINETIC ENERGY.)
INTRODUCTION TO MAGNETISM
AFTER GRAVITY, MAGNETISM IS ONE OF
THE FIRST FORCES THAT YOU BECOME
AWARE OF.
LIKE ELECTRICAL FIELDS, MAGNETIC
FIELDS CREATE FORCES ON CERTAIN
OBJECTS THAT ENTER THEM.
THE EARTH’S MAGNETIC FIELD IS NOT AS
STRONG AS ITS GRAVITATIONAL FIELD,
BUT IT EXTENDS FAR BEYOND THE
PLANET’S SURFACE.
WHAT MAKES A MAGNET?
IN 1820, HANS CHRISTIAN OERSTED PERFORMED AN EXPERIMENT WHICH
SHOWED THAT WHEN A CURRENT FLOWS THROUGH A WIRE, A MAGNETIC
FIELD EMANATES FROM THE WIRE. RECALL THAT A CURRENT IS JUST
ELECTRONS FLOWING. YET ALL ATOMS CONTAIN MOVING ELECTRONS
(WHICH ARE BASICALLY JUST TINY ELECTRIC CIRCUITS), SO WHY ISN’T
EVERYTHING MAGNETIC?
BECAUSE MOST OF THE TIME, THE
ATOMIC MAGNETIC FIELDS
CREATED BY THE ELECTRONS ARE
RANDOMLY ORIENTED, SO THEY
CANCEL EACH OTHER OUT. IN A
MAGNET, THE LITTLE ATOMIC
MAGNET FIELDS ARE ORGANIZED,
ALL POINTING IN THE SAME
DIRECTION AND THUS WORKING
TOGETHER.
ALL ELEMENTS
PARAMAGNETIC
(ALIGN IN AN EXTERNAL MAGNETIC FIELD)
Co, U+4, Fe, Ni, Al, O, Na, Cu+1, …
FERROMAGNETIC
(REMAIN ALIGNED AFTER THE MAGNETIC FIELD IS REMOVED)
Fe, Ni, Co
THE FAMOUS EXPERIMENT PERFORMED BY THAT
GREAT DANE, HANS CHRISTIAN OERSTED (1777 –
1851) IN 1820 SHOWED THAT ELECTRICITY COULD
MAKE MAGNETISM.
THIS PHENOMENON IS EXPLOITED IN ELECTROMAGNETS, WHICH ARE PART OF
CONSTRUCTION & DEMOLITION, TAPE DECK HEADS, MRI MACHINES, BULLET
TRAINS, MICROWAVE OVENS, AND LOTS OF OTHER COOL THINGS.
INDUCED VOLTAGE
SO OERSTED PROVED THAT MOVING ELECTRONS (e.g. A CURRENT) CAN
PRODUCE A MAGNETIC FIELD.
IT TURNS OUT THAT THE REVERSE IS ALSO TRUE - A MOVING MAGNETIC
FIELD CAN PRODUCE A CURRENT. THE FORMER PHENOMENON IS EXPLOITED
IN A MOTOR. THE LATTER IS THE IDEA BEHIND A GENERATOR. THIS TYPE
OF CURRENT PRODUCTION IS CALLED “ELECTROMAGNETIC INDUCTION”.
Ford Model T
1908 - 1927
THE BIG PICTURE
ELECTRIC FIELDS AND MAGNETIC FIELDS ARE THE INGREDIENTS IN ALL
ELECTROMAGNETIC RADIATION. LIGHT WAVES, X-RAYS, RADIO WAVES,
HEAT, ETC. ARE TORRENTS OF THESE TWO FIELDS TRAVELLING TOGETHER IN
TRANSVERSE FASHION:
HAVING LEARNED ALL ABOUT LENSES AND MIRRORS, WHAT CAN WE DO
WITH THEM? WE CAN LOOK AT THINGS THAT ARE VERY SMALL & CLOSE
AND LARGE & DISTANT. A TELESCOPE DOES THE LATTER.
WHAT DOES THE FORMER? (I.E. LOOK AT THINGS VERY SMALL & CLOSE?)
TELESCOPES HAVE BEEN AROUND SINCE THE 1500’S
(POSSIBLY EARLIER), SO THEY’RE NOT VERY COMPLEX.
BY THE 1600’S, THEY WERE IN COMMON USE BY
PIRATES, SCIENTISTS, MARINERS AND ANYONE ELSE
WHO WANTED TO SEE THINGS AT A DISTANCE. NOW
THEY CAN BE AS SMALL AS TOILET PAPER TUBE OR AS
BIG AS A BUS.
ANOTHER NAUTICAL TOOL IS CALLED A SEXTANT. IT WAS INVENTED IN
1757 AND USES MIRRORS AND A LENS TO TAKE SIGHTINGS FROM THE
SUN AND STARS IN ORDER TO FIND ONE'S LATITUDE AND LONGITUDE.
SEXTANTS MEASURE THE ANGLE BETWEEN TWO OBJECTS.
THESE MEASUREMENTS ALLOWED NAVIGATORS TO PLOT A COURSE ON A
CHART. TO FIND LATITUDE, SIGHTINGS ARE MADE BETWEEN THE
HORIZON AND A STAR OR THE SUN. LATITUDE IS FOUND BY TAKING A
MEASUREMENT BETWEEN THE MOON AND A STAR. NO NEED FOR G.P.S.!
THERE ARE 2 BASIC TYPES OF TELESCOPES THAT WE COVER IN THIS
CLASS: REFRACTING AND REFLECTING (WHICH IS EXACTLY WHAT
LENSES AND MIRRORS DO!)
THE MAGNIFICATION OF A TELESCOPE IS THE FOCAL LENGTH OF
THE OBJECTIVE LENS OR MIRROR
(WHY IS IT CALLED THE “OBJECTIVE”?)
DIVIDED BY THE FOCAL LENGTH OF THE EYEPIECE LENS
Practice problems:
A telescope has an objective focal length (OFL) = 250mm and an eyepiece
focal length (EFL) = 100mm, what is its magnification?
OFL = 75mm and EFL = 15mm. M = ?
EFL = 8” and OFL = 32”.
M=?
THIS IS A REFLECTING TELESCOPE. RECALL THAT MIRRORS HAVE
FOCAL POINTS TOO. THEY USE THE SAME MAGNIFICATION
EQUATION.
EXTEND THE RAYS GOING FROM THE CONVERGING MIRROR TO THE
FLAT MIRROR AND INDICATE WHERE ITS FOCAL POINT IS.
TIME FOR A VIDEO!
PLANETS AND STARS ARE AFFECTED BY GRAVITY, BUT WHY SHOULD WE CARE?
WE KNOW THAT WHEN WE WANT TO LAUNCH AN OBJECT OVER A
DISTANCE, WE MUST GIVE IT SOME UPWARD VELOCITY TO GIVE IT
TIME TO MOVE BEFORE GRAVITY BRINGS IT BACK DOWN AGAIN.
NOTE THAT GRAVITY
ONLY PULLS THESE
OBJECTS DOWN. IT
HAS NO HORIZONTAL
INFLUENCE. THE
VERTICAL AND
HORIZONTAL
COMPONENTS OF THE
OBJECT’S MOTION
ARE INDEPENDENT OF
EACH OTHER.
THE EARTH’S SURFACE CURVES AROUND.
IT DROPS DOWN ABOUT _____ FOR EVERY
_____ YOU MOVE LATERALLY.
WHICH GREEK GOD IS SHOWN
HERE HOLDING UP THE EARTH?
FAMOUS GRAVITY GURU ISAAC
NEWTON PONDERED THAT EVEN
WITHOUT ANY VERTICAL
COMPONENT, A CANNONBALL
FIRED HORIZONTALLY WOULD
STILL TRAVEL SOME DISTANCE
BEFORE HITTING THE DIRT.
WHAT WOULD HAPPEN IF THE CANNONBALL WERE FIRED SO FAST
THAT ITS PARABOLIC PATH MATCHED THE CURVATURE OF THE
EARTH? WHAT IF IT TOO TRAVELED 8Km AS IT DROPPED 5m?
IT TURNS OUT THAT THIS MAGICAL
SPEED IS 8 Km/sec (AROUND 18,000
MPH!) TOO FAST FOR BULLETS OR
CANNONBALLS, BUT EASILY
ACCOMPLISHED BY SATELLITES. SPEEDS
FASTER THAN 8 Km/sec WILL RESULT IN
AN OVAL ORBIT (CALLED AN ELLIPSE.)
LIKEWISE, THE MOON IS “FALLING” AROUND THE
EARTH, AND ALL THE PLANETS ARE “FALLING”
AROUND THE SUN!
THAT’S WHY WE CARE ABOUT GRAVITATIONAL FIELDS. THEY
AFFECT THE MOTION OF DARN NEAR EVERYTHING IN THE WHOLE
UNIVERSE! IT TURNS
OUT THAT ALTHOUGH
PLANETS AND MOONS
ARE TYPICALLY
ILLUSTRATED
ORBITING IN
CIRCULAR PATHS,
THEY VERY RARELY
ARE. THE ORBIT IS
TYPICALLY AN ELLIPSE.
AN ELLIPSE IS DIFFERENT FROM A
CIRCLE BECAUSE IT HAS TWO
“CENTERS”. THEY’RE ACTUALLY CALLED
FOCI (PLURAL OF FOCUS.) RECALL
THAT A CIRCLE IS MADE FROM ALL THE
POINTS IN A PLANE THAT ARE EQUALLY
DISTANT FROM A FIXED POINT.
WHAT IS THAT FIXED POINT (THE
CENTER DOT) CALLED?
WHAT ARE THE LINES CALLED?
AN ELLIPSE IS A STRETCHED-OUT CIRCLE, SO THE CENTER GETS
STRETCHED OUT TOO. THE INTERIOR DOTS ARE THE FOCI. THE
TOTAL DISTANCE FROM THE FOCI TO ANY POINT ON THE ELLIPSE IS
A CONSTANT NUMBER. THAT NUMBER IS ALSO EQUAL TO ANOTHER
IMPORTANT DISTANCE CALLED THE MAJOR AXIS.
FILL IN THE MISSING ADJECTIVES IN THIS DIAGRAM:
THE MAJOR AXIS IS TWICE AS LONG AS THE __________________.
A COMPASS IS A GREAT TOOL FOR DRAWING A
CIRCLE, BUT IT WON’T HELP YOU DRAW AN
ELLIPSE.
BUT TWO NAILS AND A
PIECE OF STRING WILL HELP
YOU MAKE A NIFTY OVAL!
WHAT PART OF THE ELLIPSE
DO THE NAILS REPRESENT?
AND NOW, TIME FOR A
FINAL QUICK VIDEO!
RECALL NEWTON’S FIRST LAW: OBJECTS
MAINTAIN THEIR MOTION FOREVER IF
THERE’S NO OUTSIDE FORCE ACTING ON
THEM. THE AIR HOCKEY PUCK CONTINUES
IN A STRAIGHT LINE AT A CONSTANT SPEED
UNTIL THE WALL OR A PADDLE HITS IT.
GOING AROUND IN A CIRCLE IS A CONTINUAL CHANGE IN MOTION
BECAUSE THE OBJECT’S DIRECTION IS CONSTANTLY CHANGING, AND
THAT REQUIRES A CONTINUAL APPLICATION OF AN OUTSIDE FORCE. IN
EACH PHOTO, DRAW AN ARROW REPRESENTING THAT FORCE. START
THE ARROW IN THE MIDDLE OF THE OBJECT THAT’S CIRCLING AROUND,
AND POINT IT ALONG THE LINE OF THE APPLIED FORCE (AS SHOWN IN
THE PHOTO BELOW).
NOTICE HOW THE FORCE ALWAYS POINTS TOWARD THE CENTER OF THE
CIRCLE. “CENTER POINTING” MEANS “CENTRIPETAL” IN GREEK.
FOR CELESTIAL BODIES, THAT CENTRIPETAL FORCE
IS GRAVITY. WITHOUT THE GRAVITATIONAL PULL
FROM THE SUN, ALL THE PLANETS WOULD FLY AWAY
WITH A VELOCITY THAT’S TANGENT TO THE ORBIT
THEY WERE MAKING WHEN THE GRAVITY GOT
TURNED OFF.
THE MOVEMENT OF PLANETS AROUND STARS
(OR MOONS AROUND PLANETS) IS THE
RESULT OF A TUG-OF-WAR BETWEEN
NEWTON’S FIRST AND SECOND LAWS: THE
TENDENCY OF AN OBJECT TO MAINTAIN ITS
VELOCITY, AND HOW THAT VELOCITY IS
CHANGED WHEN A FORCE ACTS ON IT.
AMAZINGLY, GRAVITATION FIELDS CAN EVEN AFFECT
THE MOTION OF LIGHT (WHICH DOESN’T HAVE ANY
MASS!) NEWTON WOULDN’T HAVE BELIEVED IT, BUT
EINSTEIN PREDICTED IT (AND HE WAS RIGHT). OUR
NEXT VIDEO DISCUSSES HIS HYPOTHESIS AND THE
EXPERIMENT THAT MADE ALBERT EINSTEIN FAMOUS
(NOT JUST IN THE SCIENTIFIC COMMUNITY, BUT
AROUND THE WORLD.) THE PHENOMENON IS CALLED
“GRAVITATIONAL LENSING” BECAUSE EXTREMELY LARGE
GRAVITATIONAL FIELDS CAN BEND LIGHT JUST AS A LENS DOES.
COMPARED TO OTHER FORCES (LIKE MAGNETIC OR ATOMIC), GRAVITY IS A
VERY WEAK FORCE (ALTHOUGH ITS REACH IS QUITE IMPRESSIVE.) WE
WON’T BE CALCULATING IT IN THIS CLASS, BUT THE GRAVITATIONAL FORCE
BETWEEN TWO OBJECTS DEPENDS ON THEIR MASSES AND HOW FAR APART
THEY ARE.
NOTE THAT THIS EQUATION HAS
THE SAME DENOMINATOR AS THE
EQUATIONS FOR THE SPREADING
OF LIGHT AND SOUND WAVES
(INVERSE SQUARE.)
WHAT’S THE “G” FOR? CONSIDER THIS COMPARISON:
BIGGER CIRCLES HAVE BIGGER DIAMETERS. A
DIAMETER AND A CIRCUMFERENCE ARE NOT THE
SAME LENGTH, BUT THEY ARE RELATED. HOW? BY
THE EQUATION C =
D
THE EQUATION C = D IS WRONG. THE NUMBER
MAKES IT RIGHT. THE “G” IN THE GRAVITY
EQUATION SERVES THE SAME PURPOSE – IT’S A
CONSTANT JUST LIKE
IS, AND IT INTRODUCES THE CORRECT BALANCE TO
MAKE THE EQUATION TRUE. HOW WEAK IS GRAVITY?
G = 0.0000000000667!
THAT’S WHY YOU NEED A LOT OF MASS TO EXHIBIT A READILY NOTICEABLE
GRAVITATIONAL FIELD. ALTHOUGH PETER GRIFFIN SEEMS TO DOUBT THAT.
BUT ALL OBJECTS HAVE MASS
AND THEREFORE A GRAVITATION
FIELD AROUND THEM. IN “STAR
WARS”, YODA EXPLAINED TO
LUKE THAT THE FORCE WAS
EVERYWHERE – HE WAS RIGHT.
WISE JEDI WAS HE.
JUST AS MAGNETS WILL MOVE FASTER AS THEY GET CLOSER TOGETHER
AND A FALLING BODY SPEEDS UP AS IT GETS CLOSER TO THE EARTH,
AN ORBITING BODY WILL SPEED UP AS IT GETS CLOSER TO THE SUN.
THE OTHER “CENTRAL” IDEA WE
NEED TO INTRODUCE IS CALLED
ANGULAR MOMENTUM. INDIANA
JONES KNOWS ABOUT LINEAR
MOMENTUM. RELATED TO
NEWTON’S 2ND LAW, IT IMPLIES
THAT SMALLER OBJECTS MOVE
FASTER THAN LARGER ONES GIVEN
THE SAME FORCE. SO AS THE WHIP
GETS SMALLER, IT GOES FASTER.
ICE SKATERS, GYMNASTS, HIGH-DIVERS, AND CATS UNDERSTAND ANGULAR
MOMENTUM. AS THEIR RADIUS GETS SMALLER, THEY SPIN FASTER.
A FALLING CAT WILL WITHDRAW AND
STRETCH ITS LEGS AND TORSO TO SPIN
ITSELF AT THE RIGHT SPEED AT THE RIGHT
TIME SO IT LANDS ON ITS FEET. THE TAIL
HELPS TOO. CATS THAT FALL OUT OF
APARTMENTS ABOVE THE 2ND FLOOR
ACTUALLY HAVE A HIGHER SURVIVAL RATE
THAN THOSE WHO FALL SHORTER
DISTANCES BECAUSE THEY HAVE MORE TIME
TO GET THEIR FEET UNDER THEM BEFORE
THEY LAND.
JUST LIKE BUBBLES
GOING DOWN A
DRAIN, AS PLANETS
(OR OTHER
CELESTIAL BODIES)
GET CLOSER TO THE
SUN, THEY MOVE
FASTER.
AN INVERSE RELATIONSHIP EXISTS
BETWEEN THE PLANET’S SPEED AND ITS
DISTANCE FROM THE SUN. IF THE PLANET
DOUBLES ITS DISTANCE, IT WILL GO HALF
AS FAST. AT ¼ THE DISTANCE, IT WILL GO 4
TIMES FASTER.
PLANETARY IDENTIFICATION LAB
Purpose:
Your job will be to identify each object on the following pages (Object A, Object B, and
Object C) based upon their orbital characteristics.
Procedure:
ON THE DIAGRAM OF THE ORBIT FOR EACH OBJECT, DO THE FOLLOWING:
1. Using the colored pens provided, draw the
“crosshairs” and label them as shown. Draw the
Major Axis in black, the Minor Axis in blue, and the
Semi-Major Axis in red. Do not draw the SemiMajor Axis (SMA) through the sun.
2. Measure the length of the SMA in centimeters and
record it where indicated on the back of this page.
Remember that this is the planet’s average
distance away from the sun.
3. Measure the distance from the center of the ellipse
to the sun (in centimeters) and record it likewise.
4. Divide the smaller number by the bigger one to
calculate the eccentricity of the object’s orbital
ellipse.
5. Using the scale given on each diagram, convert
the centimeters (cm) to Astronomic Units (A.U.) and
record that distance.
6. Use the chart below to identify the orbiting body.
7. Record your data and conclusions below:
OBJECT A:
Distance from center to far edge of orbit (SMA) = __________ cm  ________ A.U.
Distance from center to the sun = __________ cm  ________ A.U.
eccentricity =
Average distance from sun to orbiting body = ________ A.U.
The object is:
OBJECT B:
Distance from center to far edge of orbit (SMA) = __________ cm  ________ A.U.
Distance from center to the sun = __________ cm  ________ A.U.
eccentricity =
Average distance from sun to orbiting body = ________ A.U.
The object is:
OBJECT C:
Distance from center to far edge of orbit (SMA) = __________ cm  ________ A.U.
Distance from center to the sun = __________ cm  ________ A.U.
eccentricity =
Average distance from sun to orbiting body = ________ A.U.
The object is:
8. Use Kepler’s Third Law (P2 = a3) to calculate the period of orbit for each object.
Object A:
Object B:
Object C:
Based upon the orbital data, do you conclude that object A and object B follow Kepler’s
Third Law? Explain your reasoning.
Names:
Date:
Period:
Recall drawing an ellipse (oval). Unlike a circle, it has different radii
(measured from its center). Instead of having 1 center point, it has 2 foci.
As shown here, the distance from one focus to a point on the ellipse, then
back to the other focus, is the same for every point on the ellipse (in fact,
that’s the definition.) As implied by Kepler’s Third Law, there are two
others. The First Law addresses planetary geometry. Kepler’s First Law
states that all planets follow an elliptical orbit around the sun, and the sun is
one of the foci (there’s nothing at the other.)
Kepler’s Second Law examines what happens as a planet changes speed
during its orbit. Kepler realized that a planet will cover the same amount of
area at all times. Using 2 weeks as an example, a planet will cover the
same amount of area during any 2-week period, no matter where it is in its
orbit. Consequently, this is sometimes also referred to as The Law of
Equal Areas. (Note that this amount is unique to each planet. The area
for different planets will be different in that same 2-week period.)
The number of
boxes between A
and B is the same as
between H and I.
Kepler presented
both these laws in
1609. It would take
another decade to
formulate the Third
Law.
Now we can summarize the three laws:
Although the planets are typically illustrated as equally-spaced from the sun,
their actual distance gets bigger as they get farther from the sun.
NOT ALL ORBITS ARE CREATED EQUAL. ALTHOUGH THEY’RE ALL
ELLIPTICAL, SOME ARE ROUNDER AND SOME ARE FLATTER. THIS ASPECT
OF AN OVAL IS CALLED ITS ECCENTRICITY. THE SYMBOL IS e AND IT IS
EQUAL TO HALF THE DISTANCE BETWEEN THE FOCAL POINTS DIVIDED BY
THE SEMI-MAJOR AXIS.
IF THE UPPER HORIZONTAL LINE IS 12 MILLION MILES LONG AND THE
LOWER (SHORTER) LINE IS 9 MILLION MILES LONG, THEN THE ORBIT’S
ECCENTRICITY IS EQUAL TO 9,000,000 MILES ÷ 12,000,000 MILES = 0.75
AN ECCENTRICITY MUST BE BETWEEN ZERO AND ONE. A PERFECT CIRCLE
HAS AN ECCENTRICITY OF ZERO AND FOR A STRAIGHT LINE IT EQUALS 1.
KNOWING A PLANET’S ORBITAL ECCENTRICITY CAN PROVIDE AN
ADDITIONAL CLUE FOR IDENTIFICATION IF THE PERIOD OF ORBIT (FROM
KEPLER’S 3RD LAW) IS UNKNOWN, OR VERY CLOSE TO ANOTHER PLANET’S.