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Demo Corner

# Relative Motion Demo: The River Question

Ryan Thompson, OAPT Treasurer, Physics Teacher, Newmarket HS
superryanthompson@gmail.com

I purchased this little magnetic moon rover at Masterminds for \$6 a few years ago because I thought it was cool. I didn’t have any specific ideas on how to utilize it until a few years later when I was teaching the famous river question to students. You know how it goes: Alice is crossing a river that has a velocity with respect to the shore of 4 m/s [East] and Alice swims with a velocity of 3 m/s [South] with respect to the water. If the river is 60 m wide, how long does it take Alice to get to the other side? The concept that is hard for students to reconcile is that even though Alice is being pushed to the right from the shores frame of reference, the amount of time to get to the other side is independent of the river’s velocity. This is when I had a Eureka moment. I grabbed the moon rover and put it on our whiteboard. I then wound it up and let it go south, just like Alice would. Read More...

# Buoyancy and Newton’s Third Law of Motion

Ernie McFarland University of Guelph
elm@physics.uoguelph.ca

This article is excerpted from Physics in Canada, Volume 61, No. 2, (2005), pg. 87-89, with permission of the Canadian Association of Physicists (CAP).

In recent years the active engagement of students in physics classes has become increasingly common, especially with the publication of Eric Mazur’s book “Peer Instruction” (Prentice Hall, 1997). A frequently used format is to pose a multiple-choice question, and ask the students to discuss the question in small groups and vote on the possible answers by a show of hands or computerized remote-control technology (“clickers”). This basic approach can be used with a question about the possible outcomes of a lecture demonstration. The instructor shows the demonstration apparatus and states what will be done with it, but does not perform the demonstration nor indicate what the result will be. Students discuss the possible outcomes and vote on them, and then the demonstration is completed to show what actually happens, and the relevant physics is discussed. Read More...

# Mystery of a Pulled Spool

Tetyana Antimirova, Department of Physics, Ryerson University
antimiro@ryerson.ca

One of the ubiquitous simple physics demos that works equally well for all audiences from small children to the students in the introductory mechanics course is a plastic or wooden spool (or yo-yo) with a string wound around it. A virtually no-cost version of the “demo equipment” is a spool of common household sewing thread. Being curious, I did a Google search on yo-yo, and the search produced about 120,000,000 results! Read More...

# Videos of Nonlinear Self-organizing Phenomena

Stephen Morris, Department of Physics, University of Toronto
smorris@physics.utoronto.ca

Many of the ordered structures that we see in the natural world are self-organized in the sense that they emerge spontaneously from the normal operation of the underlying laws of physics, but in a way which is not at all obvious from those laws, and with some regular order which is not due to external guiding forces. Ripples on the sand at the beach (Fig. 1) are an example; somehow the action of the turbulent waves on the individual grains conspires to form the ripples, a highly organized patterned state. The wavelength of the ripples is not at all obvious in the basic physics of water-sand interaction. Read More...

# GPS Meets Einstein

Damian Pope, Senior Manager of Outreach Perimeter Institute for Theoretical Physics
dpope@perimeterinstitute.ca

Column Editor’s Note: The author of this article presented a fascinating talk about this topic at the 2010 OAPT Conference. Via the weblink provided in the article, readers can obtain access to a very useful student activity that demonstrates the importance of relativity in the operation of GPS.

The Global Positioning System (GPS) is one of the twentieth century’s greatest engineering marvels. Today, it’s the backbone of billions of dollars of economic activity. It’s used by a vast array of occupations including farmers, construction workers, doctors and even professional athletes. And all this comes on top of the more familiar personal applications like satellite navigation in cars and for hiking.

As well as being immensely practical, the GPS also involves some pretty cool physics — even, strangely enough, Einstein’s theory of relativity. Read More...

# The Belt-Hanger

Ernie McFarland University of Guelph
elm@physics.uoguelph.ca

This article first appeared in the OAPT Newsletter in 1987. It is being repeated here for three reasons: the demonstration is a classic, 1987 was a long time ago, and now this demo (and others) can be seen online (use the link at the end of the article).

One category of good physics demonstrations involves the “disorientation” or “disequilibrium” of students. The demonstrations in this category cannot be explained by most students, and thus serve to disorient the students into a state of disequilibrium from which they wish desperately to escape. Read More...

# Can You See Sound?

Bonnie Lasby, Physical and Engineering Science Dean’s Office University of Guelph
blasby@uoguelph.ca

This demonstration is a nice way to show that sound is vibration of molecules. The picture below shows the equipment required for this demonstration. The setup consists of an amplifier attached to an input device (laptop, iPod, mp3 player, etc) and a set of small speakers (described below) as well as a bar clamp and red and green laser pointers. Read More...

# How to Make a Lighted Throwing Stick to Show that the Centre of Mass is a “Special Place”

Forest Fyfe, Department of Physics and Atmospheric Physics Dalhousie University

Illustrating the concepts of centre of mass and centre-of-mass motion to an introductory physics class can be a challenge to a physics instructor. The topic can be very mathematically complex and is not necessarily intuitively obvious. A device that demonstrates how the centre of mass of an object moves as compared to the motion of a point on the object away from the centre of mass would provide an excellent qualitative illustration of this. At Dalhousie University we have constructed just such a device, our lighted throwing sticks. Read More...

# Making Speakers

Bonnie Lasby Physical and Engineering Science Dean’s Office University of Guelph
blasby@uoguelph.ca

I prefer to do this as an activity as opposed to a demonstration, and have found that it works very well for students in Grades 7 to 12 visiting the University. I start with a discussion about sound and then compare a speaker to the human ear. In the discussion on speakers, I also talk about magnets and how they work, and I explain the difference between permanent magnets and electromagnets. After this discussion, I explain how to make speakers using a plastic cup, a magnet, and a coil of wire. Each student makes his/her own speaker and then tests it. Read More...

# An Inexpensive Magnetometer

Dave Doucette (OAPT President) Richmond Hill High School, Richmond Hill, Ontario

Several years ago I was in need of a cheap, easily assembled, sensitive magnetometer. The intent was to design a tool for students to palpably observe the magnetic field around a current carrying conductor. Deflection of a compass needle lacked the ‘wow factor’ I sought. The solution turned out to be beautiful in its simplicity. Read More...

# Bernoulli’s Principle

Martin Williams, Department of Physics, University of Guelph
martin@physics.uoguelph.ca

In this demonstration, we utilize simple everyday household items to test Bernoulli’s principle and verify the apparent counterintuitive nature of its predictions. Read More...

# Wire Fire!

Joanne O’Meara, Department of Physics, University of Guelph
omeara@physics.uoguelph.ca

This demonstration is a nice way to illustrate the P = I 2R relationship that is discussed in electric circuits. Figure 1 illustrates the equipment: a Variac transformer takes the wall output of 120 V and generates a variable voltage from 0 to 140 V. This is then sent through a Hammond Manufacturing transformer (167X5), converting down to 5 V output. We use this second transformer in order to increase the current through the wires. The output from the second transformer is connected to three wires in series: approximately 10 cm in length of each of ~18 gauge Nichrome, steel and copper. A piece of folded paper is placed on each wire. Read More...

# An Ultimate Elevator Ride: Weight and Apparent Weight Demonstration

Marina Milner-Bolotin, Department of Physics, Ryerson University
mmilner@ryerson.ca

We all know that some concepts are harder for students to comprehend than others. The concepts of weight, apparent weight and weightlessness are often stumbling blocks for many of our students. Apparently they are also somewhat confusing for the seasoned scientists and engineers. While visiting the Lyndon B. Johnson NASA Space Centre in Houston, TX, I had a unique opportunity to have lunch at the “Zero-G Diner”1. Apparently, the Space Centre Houston is located at a special place where Newton’s Law of Universal Gravitation does not hold and should be modified. Read More...

# Total Internal Reflection

Diana Hall, Bell High School, Nepean, Ontario

A fun example of total internal reflection can be created with an aquarium tank or similar transparent container filled with water. Students enjoy wandering around the tank with objects placed around on all sides including above and below. Sometimes you can see what you appear to be looking at and sometimes not. Students are challenged to draw ray diagrams to show why you cannot see certain objects but can unexpectedly see others from certain angles. One example is shown here. It’s definitely a good seed for discussion. Probably a good coffee table display for your parties too. Read More...

# Air Column End

Diana Hall, Bell High School, Nepean, Ontario

Here’s a really easy way to show students that the pressure at the end of an open-air column doesn’t change exactly at the physical end of the tube. It requires a motion sensor, a tube, and the right-sized insert for the tube. I happen to have a plexiglass tube into which a tub of play-doh fits just nicely. Read More...

# Simple Centre of Mass Demonstrations

Tetyana Antimirova, Ryerson University
antimiro@ryerson.ca

There are several very simple demonstrations on centre of mass that can be performed with everyday objects. In this article I describe a couple of demonstrations that I do with my students. Read More...

# Water Rockets

Rolly Meisel
rollym@vaxxine.com

Having students construct and launch a water rocket is an entertaining way to investigate Newton's Third Law of motion. Students can construct the rockets at home for an in-class launching session. Read More...

# Seeing and Photographing High Speed Events

Martin Fischer, Science Education Branch, Ontario Science Centre
martin.fischer@osc.on.ca

See the shards of a popping balloon, watch water drops suspended in the air or witness glass shattering — all of it seemingly frozen in time. Some of these events last less than one thousandth of a second but you can see them with your own eyes, thanks to the persistence of vision and a homemade sound trigger that releases a camera flash at exactly the right moment. Read More...

# A Demonstration of the Production of Sound

John Vanderkooy, Distinguished Professor Emeritus Department of Physics and Astronomy, University of Waterloo

For this demonstration, a small open loudspeaker driver is necessary, driven from a sound source with output power sufficient for a loudspeaker. A ghetto-blaster is convenient if it has an output jack or can be modified to direct the loudspeaker output to an external device. For best results the small driver should be of moderate or better quality. It helps if its compliance is high so that bass notes cause substantial cone motion. Read More...

# Physics and Music: Harmonics

Diane Nalini de Kerckhove, Department of Physics, University of Guelph

Diane Nalini de Kerckhove is an Assistant Professor in the University of Guelph’s Department of Physics. She is also a singer/songwriter and recently launched her third CD, “Songs of Sweet Fire”, a collection of Shakespeare songs and sonnets set to her original jazz and blues music.

I have never met anyone who doesn’t like music. After teaching the physics of waves at various levels over the years, I’ve come to realize that demos involving music have a wide appeal with students, especially since most of them have studied an instrument at some point or another. Here are two options for exploring harmonics of standing waves. Read More...

# Demonstration of a Variable Tension in a Pendulum’s String

Marina Milner-Bolotin, Department of Physics and Astronomy University of British Columbia, Vancouver

A very effective demonstration of a variable tension in a swinging pendulum can be performed using very simple equipment. Read More...

# Induction Puzzle

Leigh Palmer, Simon Fraser University

Here's a demonstration that will make your students think more carefully about the meanings of the terms voltage, electromotive force, and potential difference. A transformer is necessary for the demonstration. Read More...

# Sound Tube: A Versatile and Inexpensive Physics Demonstration

Debbie Chaves and Bruno Tomberli, Physics Department, University of Guelph, Guelph, Ontario, N1G 2W1

A versatile and inexpensive demonstration tool for every physics teacher is the “sound tube,” also known as the whirly, Hummer and corrugahorn. Its puzzling properties span many different physics topics. Read More...

# The World’s Simplest Motor

John Pitre, University of Toronto

In the December 2004 issue of The Physics Teacher, Christopher Chiaverina described a motor consisting of four components: a battery, a cylindrical rare earth magnet, a small piece of copper wire, and a steel nail. Since I know that many of our members do not have ready access to this journal, I have essentially reproduced his article here. Read More...

# Demonstration Cart or “Happy Wagon”

Stuart Quick, Department of Physical & Environmental Sciences University of Toronto @ Scarborough

Some teachers might find it awkward and inconvenient to set up demonstrations on lab stands and take them down again in the time at their disposal. Lab stands tend to be weak affairs that wobble with even small loads. Or teachers may find setting up more than one demonstration at a time impractical. Read More...

# Reversal of Spectral Lines

Dr. Eknath V. Marathé, St. Catharines, Ontario

Spectroscopy has contributed to our knowledge not only of Earth but also of the Sun, interstellar space, distant stars and galaxies. The subject of spectroscopy began in the year 1666 with the discovery by Newton that when the Sun’s rays are allowed to pass through a prism, they produced a band of colours which he called a spectrum. In 1802, William Hyde Wollaston, (1766 – 1828, English chemist and physicist) used a narrow slit as a secondary source of light and observed dark lines in the spectrum of sunlight. Wollaston thought that the dark lines were natural boundaries between various colours of the spectrum. Read More...

# Rotational Motion and the Chain Saw

John Caranci
physix1@look.ca

This demonstration is used to introduce rotational motion by using the complex motion of a chain-saw chain. You probably have seen many demonstrations over the years but this is one that can be done with the simplest equipment: one elastic band and a sheet of newsprint. Read More...

# Motion of the Centre of Mass 2

Patrick Whippey, Department of Physics & Astronomy, The University of Western Ontario

Do we really believe Newton’s Laws? This demonstration was born many years ago when a perceptive student challenged the assertion that a body free to move always rotates about its centre of mass. This demonstration requires an air table. Read More...

# Motion of the Centre of Mass 1

Patrick Whippey, Department of Physics & Astronomy, The University of Western Ontario

Do we really believe Newton’s Laws? This demonstration was born many years ago when a perceptive student challenged the assertion that a body free to move always rotates about its centre of mass. This demonstration requires an air table. Read More...

# Seeing the Speed of Sound

Diana Hall, Bell High School, Nepean, Ontario

This demonstration allows students to get an idea for how slow sound actually travels. Read More...

# Pressure vs. Particle Movement — The Dance

Diana Hall, Bell High School, Nepean

When discussing standing waves in air columns most textbooks focus on the movement of particles and show nodes at closed ends and antinodes at open ends. When thinking about the loudness of sound we have to remember that the sound is loud when the pressure difference is the greatest and that sound is a longitudinal wave. This occurs at nodes (where particles move the leave) and not the antinodes (where particles move the most). I use my students to demonstrate this difference. Read More...

# Superposition Principle-Kicking the Canister

Diana Hall, St. Charles North HS, Illinois

My students have fun predicting which canisters will get knocked down in an interference demonstration. We stretch out a long spring across the classroom floor. We then line up film canisters (or other substitutions) alongside the spring. Students predict which ones will get knocked over and which will be left standing. They must also say why. Read More...

# Acoustical Wheel with Christmas Tree Balls

Christian Ucke, Technical University Munich
cucke@ph.tum.de

Figure 1 was taken from an old German physics textbook1 dating from 1906. So-called Helmholtz-resonators are fixed on a cross which can rotate easily on a needle bearing. With the right resonance frequency of the Helmholtz-resonators and enough acoustical power from a loudspeaker, this device starts to rotate anticlockwise (view from above). Read More...

# The Simple Demonstration of the Photoelectric Effect

Eknath V. Maratha, St. Catharines, Ontario

In 1900, Max Planck worked out a relatively simple energy radiation equation for a black body that described the distribution of radiation accurately over the entire range of frequencies. His equation was based on a crucial assumption: radiant energy is not infinitely subdivisible. Like matter, it exists in “particles.” These particles Planck called quanta, or in the singular, “quantum.” He further suggested that the size of the quantum, also known as “photon,” for any particular form of electromagnetic radiation, was in direct proportion to its frequency. In the visible spectrum, a photon of violet light would therefore contain more energy than a photon of red light. The small constant that is the ratio of the energy of a photon (E) and the frequency(v) of the photon radiation is called Planck’s constant and it is symbolized as h = E/v). It is now recognized as one of the fundamental constants of the universe. Planck’s theory, known as Quantum Theory, was applied by Einstein in explaining the photoelectric effect. Read More...

# Classroom Demonstration of Spectra

Jim Hunt, Physics Department, University of Guelph
phyjih@physics.uoguelph.ca

The availability of large sheets of plastic replica gratings has greatly increased the ability to show spectra to classroom-sized groups and, in the process, put on a nice light-show. Read More...

# Demonstrations Just for Fun

Roily Meisel, Ridgeway Crystal Beach High School
rollvm@vaxxine.com

The three demos described here are, to the best of my knowledge, nowhere in the Ontario curriculum, although I stand to be corrected. Sometimes we need to do things because they are interesting and fun, and not solely because they are “on the course”. Read More...

# Cheap and Easy Sound Demos with Rods and Tubes

Roily Meisel, Ridgeway Crystal Beach High School
rollvm@vaxxine.com

Visible standing waves with a node at each end are fairly easy to demonstrate. You can use a long spring such as a slinky (cheap way), or even order a nice transducer-based demo from one of the scientific supply companies (expensive way). However, I also wanted to demonstrate antinodes at both ends, or even one node and one antinode. Read More...

# An Electric Guitar Pickup

Peter Scovil, Waterford, ON
petescov@enoreo.on.ca

I like music, and enjoy playing the guitar, so the following demo caught my eye (or ear?). It was in the Jan. '95 issue of The Physics Teacher (p.58) by G.R. Davies of South Africa. It is a good example of electromagnetic induction that is easy for students to understand. Read More...

# Balancing on the Edge and Inexpensive Accelerometers

Diana Hall, Bell High School, Nepean
Diana_Hall@ocdsb.edu.on.ca

Diana Hall presents two simple demonstrations. Read More...

# Two-Minute Impromptu Demos

Ed van den Berg and Rosea van den Berg, University of San Carlos, Talamban Campus, Cebu City, Philippines
edberg@durian.usc.edu.ph

This article was excerpted (with the authors’s permission) from a longer article in The Physics Teacher (Sept. 1998, p.356-8).

What can we do to have clear and exciting lessons without a great amount of demonstration apparatus and hours of preparation each day? We present here a collection of small and quick demos that require no equipment beyond what is present in a classroom (chalk, chairs, students, books, paper, backpacks and their contents). Some are to prove something, but most are to illustrate, visualize, or simulate. These basic and well-tried ideas will stimulate students and revive the instructor who has spent a late night checking student papers. Have fun! Read More...

# D-Ball

Diana Hall, Bell High School, Nepean, Ontario
Diana_Hall@ocdsb.edu.on.ca

This is a very popular game I have played with my OAC physics class. It incorporates the concepts of conservation of energy and projectile motion. Read More...

# Two Sound Demonstrations

James L. Hunt Physics Department, University of Guelph
phyjlh@physics.uoguelph.ca

The following two sound demonstrations have the virtue of being inexpensive; in fact the first one costs the teacher nothing. Although I have seen the first referred to somewhere, I do not recall seeing the second. Both demonstrations rely on the human ear's remarkable ability to distinguish changes in pitch. Read More...

# Ball and Ramp Races

John Childs, Grenville Christian College, Brockville
jchilds@grenvillecc.ca

This is a good exercise to use after you’ve done kinematics, dynamics, and energy. We all talk about the kinetic and potential energy of roller coasters and their speeds, and the demonstration will let your students apply their critical thinking skills to this kind of situation. Be sure to have your students examine the setup and predict the outcome, before you run the demo. The question is: “Which ball gets to the end of the ramp first?” Read More...

# The Neon Lamp Flasher

John Childs, Grenville Christian College, Brockville
jchilds@grenvillecc.ca

This simple little homemade device can provide a very effective demonstration of AC current, it’s fun, and it’s cheap! All you need is a little neon lamp, a resistor and an AC cord. Solder one leg of the neon lamp in series with a 10K, 1/2 watt resistor, and then attach to the AC cord. Heat shrink tubing is excellent insulation for this construction, otherwise use carefully applied electrical tape. Be sure to insulate throughly, you have AC power here. Read More...

# An Inexpensive Vibrator for Standing Waves

Peter Scovil, Waterford District High School,
petescov@enoreo.on.ca

At the OAPT Conference this past June at the University of Waterloo, I gave a short demonstration of a vibrator I built from a Radio Shack speaker. It allowed me to produce longitudinal as well as transverse standing waves. This is based on an idea from one of the AAPT conference workshops. Read More...

# Lenz’s Law with Plumbing Pipes

John M. Pitre, Department of Physics, University of Toronto

In the January 1997 issue of The Physics Teacher, two articles appeared detailing the use of rare earth magnets to demonstrate Lenz’s Law in the classroom. The principle involved is that a permanent magnet falling through a tubular conductor will induce a current in the conductor and hence a magnetic field which will oppose the magnetic field of the permanent magnet and thus slow its rate of fall. This article gives variations of the methods discussed in those papers. Read More...

# A Multi-Purpose Instrument

Tomasz Dindorf and Wojciech Dindorf
Donaufelderstr. 252/24, 1220 Wien, Austria

(Editor's note: This article is reproduced, with permission, from a delightful little book, "The Sun on the Floor -Physics experiments that can be performed at home." This 68-page book describes 58 experiments that can be accomplished with simple apparatus. There are many drawings and photographs to illustrate the experiments. A single copy of the book can be ordered for only \$10 U.S. from the authors at the address above, and 20 copies can be obtained for \$100 U.S.) Read More...

# A Crazy Cantilever

George Vanderkuur, WICED Centre, TDSB
georvand@enoreo.on.ca

Bricks, books, or metre sticks are all you need for this neat demonstration. As illustrated, the top brick projects by half its length and subsequent bricks project 1/4, 1/6, 1/8, et. Brick lengths. After n bricks, the cantilever will project a distance of d = 1/2 + 1/4 + 1/6 + … + 1/(2n). This may be simplified to d = 1/2 (1 + 1/2 + 1/3 + … + 1/n). For four bricks, the projected distance is 1.04 brick lengths, and for n = 5, the distance is 1.14 brick lengths (so that the top brick is clearly out beyond the edge of the table). Read More...

# Dumb Tricks with Metre Sticks

John Wylie, Toronto French School
jwylie@tfs.on.ca

Here are two tricks, sorry, demonstrations that you can store away for when you have a few minutes to kill and all you have available is a metre stick, or when you just feel the need to show off in front of impressionable young students. They both are opportunities to prove that a knowledge of physics is better than being young and co-ordinated. Read More...

# The Levitron

Alan Hirsch, Port Credit SS, Mississauga

What physics toy have you seen that can attract the attention of every passerby in a mall during the December shopping rush? And what toy can you expect your physics students to exclaim “hey, cool” when they see it? The answer to each of these questions is the same: The Levitron: The Amazing Antigravity Top. Read More...

# Two Kinds of Polaroid Glasses

John Pitre, Department of Physics, University of Toronto

When polarized light is discussed, polarizing plastic sheet filters are always mentioned. During manufacture, this material which contains
long chain molecules is mechanically stretched into sheets resulting in the alignment of the molecules. Electrons can travel along the axis of the molecules but cannot jump from molecule to molecule. When light is incident on a polaroid sheet, the component of the electric field which is parallel to the axis of the long chain molecules causes the electrons to move, and that component is absorbed; the component which is perpendicular to the axis of the molecules is unaffected. Thus, polaroid sheets have a preferred direction, or transmission axis, which is perpendicular to the axis of the long chain molecules. Read More...

# Demonstrations with a Tesla Coil

Roland Meisel, Ridgeway Crystal Beach High School
rollym@iaw.on.ca

A Tesla coil circuit generally consists of some sort of step-up transformer along with a tuned oscillator. The B-10 coil sold by Cenco Scientific is a compact device which produces 40-50 kV at frequencies of 3-4 MHz. The schematic diagram shows an inductance connected to an AC circuit. As the AC goes through its cycle, the inductance builds up a high reverse potential (similar to the arcing at the commutator of an electric motor) which can exceed the breakdown resistance of the spark gap in the oscillator circuit. When this happens, the resistance across the gap drops effectively to zero, and causes the tuned circuit to “ring” electrically, much like hitting a tuning fork. A high-voltage high-frequency AC potential is induced at the tip. This is the “simple” explanation which high school students can usually follow. For those who wish to see the differential equations describing what is going on, may I suggest an advanced book on electrical physics! Read More...

# One-Minute Experiments

Patrick Whippey, Department of Physics, University of Western Ontario
pwhippey@julian.uwo.ca

Something wonderful happened in my Physics 21 class just before Christmas last year. There was excitement, wonder, great mutual support, and just plain fun as one hundred and twelve students demonstrated 52 experiments in 52 minutes. Read More...

# The Sailboat Problem

Eknath V. Marathe, Consultant, STS Education

The sailboat provides one of the most interesting illustrations of vector resolution. Read More...

# Gold Wedding Ring — Monkey and the Pulley

Murray D. Kucherawy, A.B. Lucas S.S., London

Effective classroom demonstrations often require tinkering with temperamental equipment. With the permission of the editor, I would like to share a “thought demonstration” that requires no equipment, but which still makes a surprising point. Read More...

# Bernoulli Lost His Marbles

Al Bartlett, University of Colorado

Fill a one-litre graduated cylinder with water; the cylinder should be about 5 to 8 cm in diameter and 30 to 40 cm tall. Take an ordinary glass marble and try to drop the marble into the water in such a way that the marble will fall all the way to the bottom without first hitting the side of the cylinder. The marble makes an audible click every time it hits the glass wall. Read More...

# Big Ben — Lenz’s Law and the Cow

John Childs, Grenville Christian College, Brockville

Two demonstrations from John Childs. Read More...

# Flying Time

Dave Erb, Red Lake District High School

This is a demonstration of centrifugal force. Read More...

# The Prisoner

John Childs, Grenville Christian College, Brockville

This is an exciting force vector demonstration, which is guaranteed to create some pandemonium in your classroom! It can be done just as a visual demonstration, or as the introduction to a stimulating and challenging problem to get everyone in the class working. Your better grade-12 students can pursue the solution to a considerable length. Read More...

Alan Hirsch, Port Credit Secondary School

Having taught senior high school physics for more than 20 years, I had thought the chances of a student discovering something I hadn't seen before while performing a typical physics experiment were remote. Thus, when OAC student Karen Whiskin was performing measurements on the wavelengths of various colours of light and yelled out, "Hey sir, come and look at this!", I was not expecting to see anything new. To my surprise and joy, Karen's discovery was also a discovery for me. Using a single diffraction grating, Karen had observed the addition of light colours and had recognized that secondary light colours were being formed from primary light colours. Read More...

# Electric Hotdog

Roland Meisel, Ridgeway Crystal Beach High School
rolameis@village.ca

A current can be run through a hotdog in order to cook it. There are commercial hotdog cookers that make use of this principle. I use it near the end of the unit on resistance in the Grade 12 Physics course. Read More...

# Reflections

George Vanderkuur, Malvern Collegiate, Toronto

A laser, chalk dust and right-angle corner made of mirror tiles show the retro-reflection of light from a corner cube mirror. (Safety note: use a low-power laser beam and take care to avoid directing the beam into the audience.) Students will also enjoy looking into the mirror and observing that the image of their face (or open eye) is always in the corner. Try this with one eye closed. Read More...

# Flipping for Physics

John Wylie, The Toronto French School

Here is a good demonstration that can be used in its simplest form to show stable and unstable equilibria or, in a more advanced version, to illustrate some finer points about moments of inertia and angular motion. The material needed could not be simpler. You need a board. There are no special requirements here except that the board be rectangular and have three distinctly different dimensions. In a pinch, I have used a good-sized physics text book held closed by a strong elastic. Most brief cases work and if students feel lucky, they can try out their calculators. Read More...

# Huge Pendulum, Centre of Mass, and Magnetic Force

John Earnshaw, Trent University

The author presents three demonstrations: a large pendulum, the centre of mass of a person, and the magnetic force on a beam of electrons. Read More...

# Colour Mixing the Economical Way

Bill Konrad, Chatham Kent Secondary School

I am sure that, in the schools of Ontario, the range of equipment presently in place to demonstrate colour mixing varies all the way from ray boxes with colour filters to expensive projectors specifically designed for that topic. Many of these may be effective but frequently one finds that the resulting colour is not exactly what theory predicts. For example, a blue light, a green light, and a red light projected onto the same area of a white screen may produce a “yellow” white or a “greyish” white. The demonstration described below gives excellent results and, in keeping with current budget constraints, is very economical. To carry it out, proceed as follows. Read More...

# Optics, Density, Holography, and Curve-Fitting

Dianne Ness, Humberside C.I.

Four demonstrations from Dianne Ness. Read More...

# The Classroom Wave

Bonnie Edwards, Our Lady of Lourdes High School, Guelph

How about a physics demonstration with hundreds of moving parts that never needs to be fixed and doesn't require storage space? Hard to believe? Try doing THE WAVE in your grade 12 physics classes. Read More...

# Standing Waves — The Can that Comes Back

Pauline Plooard, Fenelon Falls Secondary School

Two quick demonstrations from Pauline Plooard. Read More...

# Not-so-Simple Harmonic Oscillator

John Wylie, The Toronto French School

Two years ago when I was in The Netherlands for the International Physics Olympiad, the Soviet team-leader, Sergey Krotov1, demonstrated a remarkable toy, crafted to the highest standards by the technical staff at Moscow State University. It consisted of a series of simple pendulums of varying lengths which, when swung together, formed very beautiful patterns. I built one of my own which works just as well, using only bits and pieces that I found in my high school physics lab. Read More...

# Parallax and Images

T.J. Elgin Wolfe, Faculty of Education, University of Toronto

Parallax is the apparent motion of one object with reference to a second object caused by a change in position of the viewer. Involve the class in the following way to introduce this concept. Read More...

# A Not-so-Serious Parallel Circuit

Peter Zuech, Mother Teresa S.S., Scarborough

This idea was born while watching the Tonight Show. A popular entertainer demonstrated a wooden board upon which four coloured light bulbs in sockets were mounted along with a corresponding set of four coloured switches. No matter how the bulbs were rearranged in the sockets, the blue switch turned the blue bulb on and off, the red switch operated the red bulb, and so on. Johnny examined the bulbs, found them to be “normal” and was convinced that it was magic. Unable to determine how the four-bulb unit operated, we designed a simpler two-bulb version for use as a discrepant event in current electricity. Our unit used two white bulbs but coloured ones could be used as in the original unit. The only skills required to construct the unit are an ability to solder and the willingness to tinker a little. Read More...

# Virtual Image Formed by a Plane Mirror

T.J. Elgin Wolfe, University of Toronto

An interesting demonstration that makes use of the location of the virtual image formed by a plane mirror can be done with a black cloth, a small candle (about 2 cm in height), a dull dark opaque shield about 3.5 cm tall and bent at right angles, a large pane of thin window glass, two retort stands, 4 adjustable clamps, a 400 mL beaker, and coloured water. To highlight the beaker in the dim light, outline the outer edges (as viewed by the class) with masking tape. Read More...

# The World’s Simplest Speaker

Frank Allan, Science Co-ordinator, Ottawa Board of Education

The world’s simplest speaker can be constructed in a matter of seconds. Read More...

# The World’s Simplest Motor

Robert Ehrlich, Physics Department, George Mason University

The world's simplest motor can be constructed in less than five minutes. Read More...

# Making Sound Waves Visible

Bill Konrad, Kent County Board of Education

The demonstration described below was demonstrated at the OAPT conference in London in June 1989. Since there was a fair bit of interest in the details of construction of the apparatus, I thought this column would provide a convenient opportunity to give the specifications. Essentially, a speaker at one end of the closed air column is used to set up a standing wave of sound inside the column. Natural gas enters the device through two copper tubes. The gas is lit and burns at numerous holes drilled across the top of the duct. Due to differences in pressure at the nodes and loops of the standing wave inside the air column, the flames that are generated vary in height giving a visual outline of the wave inside. Read More...

# Keeping Alive the Sense of Wonder … Counter-Intuition

Doug Cunningham, Science Head, Bruce Peninsula District School

“…The whole art of teaching is only the art of awakening the natural curiosity of young minds…”

Anatole France 1921 Nobel Prize, Literature

I have always been interested in finding demonstrations that provoke and awaken the natural curiosity of students. Demonstrations that provide unexpected results, or appear on the surface to violate common sense, are particularly effective vehicles for motivation. These demonstrations or experiments are known as counter-intuitive.

# Sand and Soup

Patrick Whippey, Department of Physics, University of Western Ontario

Two intriguing demonstrations from Patrick Whippey. Read More...

# The D.C. Motor

Peter Scovil, Waterford District High School

Have you had difficulties explaining to students the complexities of the D.C. motor? Read More...

# Bloody Ballistics

George Vanderkuur, Ontario Science Centre

The heart is a mechanical pump that is used to move an incompressible fluid (i.e., blood) through a very elastic closed network of tubes. With each cycle of the “pump,” the whole system expands and contracts. Read More...

# Electrostatics with Ping Pong Balls

Gyula Lorincz, University of Toronto

Many of our old favourite electrostatics demonstrations can be improved using ping pong balls painted with graphite to replace pith balls. In particular, a simple but very sensitive electrostatic torsion balance can be used to demonstrate both the attraction of opposite charges and the repulsion of like charges. Read More...

# Overhead Projector Wave Simulator

Bill Konrad, Kent County Board of Education

The demonstration described in this column is one I learned as a teacher in summer school at the beginning of my teaching career. It is one that I have found to be very useful in teaching a number of concepts related to waves. Read More...

# Falling Faster Than ‘g’

T. Dean Gaily, University of Western Ontario

A simple lecture demonstration to illustrate that some objects do ‘fall’ with an acceleration greater than 9.8 m/s2 is constructed from two pieces of 2.5 cm × 15 cm lumber approximately 1 m in length (1” × 6” × 39”), hinged together at one end. A small marble placed in a notch at or near the end of the “falling” board can be made to fall slower than the board and land in the cup strategically placed on the falling board. Read More...

# The Electrostatic Precipitator

Roland Meisel, Ridgeway-Crystal Beach High School

An electrostatic precipitator can be assembled in less than half an hour using parts commonly found around the science department in a high school. I have used it as a demonstration in classes ranging from grade 10 general science to grade 13 physics. In addition, it has spawned several senior science projects using it as an investigative tool. Read More...

# Real Image Demonstration

Don Murphy, Sydenham High School

Many demonstrations can be made not just interesting but truly memorable by “setting up” the students a bit beforehand. A rather well-known demonstration involves a real flowerpot and a flower suspended upside down inside a box placed 2 focal lengths in front of a large concave mirror. The viewer sees an illusion of the flower being on top of the box but the image disappears when the viewer approaches too close. The apparatus on hand at our school for a similar demo is illustrated below, but in this case a real image of a light bulb is formed. Read More...

# The Thermobile and Icemobile

Peter Levan, Lockerby Composite School, Sudbury

At last year’s conference in Sudbury, Al Hirsch demonstrated his icemobile1 and I mentioned the action of a thermobile1. Some people were interested in more explanation and information on these little toys and the physics behind them. Read More...

# The Bistable Diver

Jim Hunt, Guelph Physics Department

This marks the first appearance of this column, which has been prompted by the great popularity of the demonstration sessions at our annual conference. This first column is adapted from an article in the Guelph Daily Mercury, by Jim Hunt of the Guelph Physics Department.

A fun toy which teaches a lot about hydrostatics and Archimedes’ principle can be made from some very simple items. You will need 1) a large transparent dishwashing detergent plastic bottle (see A in Fig.) with a plastic valve cap, and most importantly, with an oval cross section; 2) a cap from a ball point pen; 3) a few small paper clips. Read More...
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