VIP’s mission is to
foster communication among teachers of physics and physical science
as well as to provide unique learning experiences for teachers and
their students.
Wow!!! Gone are
the days when I would go to VAST and hope for at least one session
having something to do with physics!! Now my problem is which ones
do I choose? This VAST schedule this past fall had a wonderful spread
of physics offerings and I believe VIP has played a large roll in bringing
this about. Thanks to all who have helped.
VIP’s two sessions were not as well attended as they have been the last
couple of years, but I believe that has more to do with the abundance of offerings
than anything else – what a great problem to have. Make your plans to
attend next fall’s VAST conference at the Hotel Renaissance (Portsmouth)
November 12-15, 2003. Better yet, make plans to present at the fall VAST conference.
This will be a new venue and the program coordinator may be familiar to those
who run in physics circles – Maria Cooper. I’m sure it will be
an amazing conference well worth your effort to attend.
Our Spring Meeting will be held at UVA’s Physics Building on April 12,
2003 9:00 AM-4:00 PM. The theme of this meeting is PVC – Physics Very
Cheap! This will be a make and take session focusing on demos and labs made
from PVC and other cheap materials. Participants will walk away with their
very own set of Physics Spinners, Stadium Horn, PVC String Wave Polarizing
Filters, and Thunder Tube and more! You’ve got to be there to take home
the goodies. Funds and supplies may limit the availability of some items. Limited
items will be awarded in order of RSVP to me at ajackson@harrisonburg.k12.va.us.
I "As the Whirled Turns" when
teaching circular motion. The turntables with the magic draw pad, ramp
and ball can be found in the earth science section of a few different science
catalogs. This lab helps students to view curvilinear motion from the inertial
and non-inertial frames of reference and sets the stage. It helps to set
the stage for the concept of why Centrifugal force is a fictitious force. – Andy
Jackson
As the Whirled
Turns
Materials- turntable with “magic draw” pad, steel ball, launcher
Purpose - The student will investigate how a rotating frame of reference causes
linear motion to appear to be curved motion. The student will be able to determine
which direction this curvature appears in the northern and southern hemispheres,
and be able to explain its cause.
Northern Hemisphere
In this part of the experiment,
the rim of the turntable is the equator and the center is the North
Pole. First, clear the tablet by peeling up the orange sheet. Do this
carefully so you do not rip it, or the white sheet beneath it. Place
the launcher on the equator, with Velcro, aimed at the North Pole.
Allow the ball to roll across. Do this again while rotating the turntable
slowly counter-clockwise at a steady speed. Relative to the straight-line
path made earlier, which direction does the ball turn, left or right?
Now clear the pad again. Place the launcher on the North Pole aimed directly
at the equator. Allow the ball to roll across the pad. Do this again while
rotating the turntable slowly counter-clockwise at a steady speed. Relative
to the straight-line motion, which direction does the ball turn?
Southern Hemisphere
In this part of the experiment the rim is still the equator but the center
is now the South Pole. Clear the pad and place the launcher on the equator
aimed directly at the South Pole. Launch the ball. Now launch the ball
again while rotating the turntable slowly in a clockwise direction at a
constant speed. Relative to the straight-line path, which direction does
the ball turn, left or right?
Now clear the pad again. Place the launcher on the South Pole aimed directly
at the equator. Allow the ball to roll across the pad. Do this again while
rotating the turntable slowly clockwise at a steady speed. Relative to the
straight-line motion, which direction does the ball turn?
Just a turntable now
Now the turntable is no longer the Earth, it’s just a turntable. Place
the launcher on the edge with the Velcro. Aim it towards the center. Place
a small piece of tape on the edge directly across from the launcher. Place
a wooden block on the lab bench directly across from the launcher. Launch the
ball. Next you will launch the ball while turning the turntable slowly clockwise.
Before you do the experiment try answering the two prediction questions. Answer
these as if you were the ball.
QUESTIONS FROM THE EXPERIMENT From the ball’s
point of view Northern Hemisphere
1. When heading North the ball turned __________
2. When heading South the ball turned__________
Southern Hemisphere
3. When heading South the ball turned__________
4. When heading North the ball turned__________
Prediction – answer before doing the experiment
As a turntable
5. The Ball will hit the edge of the turntable with the tape ______
A. in front of the ball B. to
the ball’s left C. to the ball’s right
6. The Ball will hit the edge of the turntable with the block ______
A. in front of the ball B. to the ball’s left C.
to the ball’s right
7. Were your answers correct? If not describe what happened.
(3 pts)Explain why, in the Northern Hemisphere, as air masses move either North
or south, they tend to turn to their right. (You’re to explain both cases)
I use the "Waves on Slinky" lab
as my introduction to waves. It brings up many more questions than
answers and not all parts can be completed as quantitatively as the
lab suggests. You can get very good data on wave speed. You can clearly
see how the tension affects the wave speed in both types of waves as
well as how little effect the energy of the wave has on wave speed.
Amplitude and wavelength are very tough to measure directly and drive
home the point that a wave is a moving phenomenon, not a static picture.
Envisioning the amplitude of the longitudinal wave also helps point
out the difference between the two types of waves to students. Students
often need some guidance on figuring out experiments they can conduct
that will conclusively let them decide what is going on when two pulses
run into each other. Do they bounce off each other or pass through
each other? It’s hard to tell if you send two equal pulses down
the slinky towards each other. I ask them how they can make the waves
distinguishable from each other and guide them as needed. – Andy
Jackson
WAVES ON A SLINKY
CAUTION! Do
NOT over stretch or entangle the slinky. It is easy to do and impossible
to fix.
Note- New terms that you must learn are presented in UPPERCASE.
Sometimes they are defined in the lab and sometimes you will need to look
them up.
Purpose
The purpose of this activity is to measure the WAVE SPEED of TRANSVERSE and LONGITUDINAL
WAVES in a slinky, as well as their WAVELENGTH, AMPLITUDE and FREQUENCY.
You will also make observations of the properties of waves when they encounter
barriers and when they interact with each other.
Materials
Slinky, meter sticks, and stop watch.
Procedure
A. Measuring WAVE SPEED, WAVELENGTH, and FREQUENCY of
waves PULSES can be generated in a slinky stretched out on the
floor by one person holding one end firmly and another person giving his/her
end a single quick jerk sideways and back. This is called a TRANSVERSE
PULSE. A LONGITUDINAL PULSE can be generated by
one person giving a single quick push-forward-pull-back motion to one end
of the slinky.
Generate a TRANSVERSE PULSE and observe the slinky. Now
generate a LONGITUDINAL PULSE. Describe and identify each
type. WAVE SPEED is the measurement of the rate at which
the PULSE moves. In other words it is the speed of the PULSE.
Measure the WAVE SPEED for each of the two types of PULSES.
Record the wave speeds in the data table. Change the tension in the slinky
and change the energy with which you "wave". Determine what factors
affect WAVE SPEED. Do the same factors affect both types
of waves in the same manner? Remember that if you want to test a variable
you must keep all the others constant to have meaningful results.
(3 pts)In the last part of
the experiment, you saw that the ball missed the piece of tape but
ended up striking the edge of the turntable directly (or very nearly
directly) in front of the wooden block. Describe the motion of the
ball and why it ended up at the block from the frame of reference of
the tape.
(3 pts)Describe the motion of the ball and why it ended up at the block from
the frame of reference of the block.
wave type
Tension
Average Time
Wave Speed
Do the same factors affect
both types of waves in the same manner? What variables are connected
and in what manner?
A. WAVE TRAIN,
or just simply a WAVE can be generated by repeating
rhythmically the motion used earlier. All waves have WAVELENGTH and FREQUENCY.
The WAVELENGTH is the distance between any two
adjacent identical points. (See diagram)
B.
Generate a TRANSVERSE wave and measure its WAVELENGTH.
In what way does this give you a different idea about waves than
if you just study them in a textbook?
C. The FREQUENCY of
a wave is a measurement of how often the wave repeats itself in
a given unit of time. Measure the FREQUENCY of
each type of wave. Explain how you measured the FREQUENCY.
The AMPLITUDE of
a wave is a measurement of how far its maximum DISPLACEMENT is
from the EQUILIBRIUM position. Measure the AMPLITUDE of
each type of wave you are generating.
D.
Determining the relationships between wave properties:
Conduct experiments
that will allow you to answer the following questions.
1.
How are FREQUENCY and WAVELENGTH related?
2.
What happens to a PULSE when it reaches the end
of the slinky?3. What happens when two different PULSES run
into each other?
Induction Braking
Demo
- The Lenz’s Law Pendulum -
Faraday’s Law of Electromagnetic Induction says that when the flux
is changed in a piece of metal or coil an emf is induced. Lenz’s Law
says that the induced emf, due to a change in flux in metal or coil will
move to oppose any change in flux. In this demonstration, a pendulum has
a magnetic bob that swings within 1 millimeter of a piece of aluminum. The
magnet is a round donut magnet. The center of the magnet has a dowel poked
into it. The dowel rod is held onto magnet by a coating of epoxy. I used
JD Weld. The epoxy itself was magnetic and evenly covered the magnet. As
the magnetic bob swings over the metal, the flux in the metal changes. An
emf and counter magnetic field in induced in the metal and the pendulum bob
comes to rest quickly –within 2 swings.
Go to our website,
http://www.vast.org/vip, to see enlarged color construction pictures.
A great source I found for LOW COST Neodymium magnets is http://www.engconcepts.net/magnets/magnets.htm.
I used the “Super Magnets -0.75 in, OD, 0.375 in ID, 0.25 in thick:
Price - 4 for $3.00 plus shipping.
By Tony Wayne
