Download Some of my Demonstrations in Class

Some of my Demonstrations in Class
Bed of Nails
I lay on a self built bed of 1200+ nails and have a student place another 600+ nails point
down on top of me. On top of that goes a cinder block. Then the student breaks the
cinder block with a sledgehammer
This shows Conservation of Energy (energy that goes into breaking the cinder block
can’t break me). Also shows the pressure/force/area relationship p = F/A.
Superconducting Levitation of a Magnet
A magnet levitates above a superconducting disk. The disk is cooled to its
superconducting temperature of about 300 degrees below zero Fahrenheit by
immersion in liquid nitrogen. The magnet will only rotate along the symmetry axis of its
field. It is this observation, involving flux pinning, that is the key for building a magnetic
track to levitate a moving superconductor as I and several of my students have done.
Magnetic Levitation of a Superconductor
This is basically the reverse of the previous demonstration. In this case a
superconductor, cooled to superconducting temperature by liquid nitrogen, moves along
and levitates above a magnetic track. This is also a case of flux pinning.
Examination of a Superconductor
Physical examination of this superconductor reveals that it is a ceramic and a
conduction test reveals that at room temperature it doesn’t conduct electricity at all. I
have a broken piece that reveals that the material is also brittle, commenting that this
characteristic makes it difficult to form into flexible wires and hard to take advantage of
its otherwise very useful superconducting properties.
The Famed Double Slit Experiment
I do this demonstration by splitting the beam of a laser pen with a lock of my hair and
projecting the resulting interference pattern across the classroom against a wall. The
result is a crosshatching of multiple diffraction patterns. Several of my students have
also performed this experiment.
What the Double Slit Experiment Doesn’t Show
This demonstration reinforces the double slit experiment by showing what the pattern in
the double slit experiment should look like if light is composed of a stream of simple little
particles. You can show this effectively in a very low tech way by pouring a stream of
cornmeal onto a piece of paper with two holes cut it in. Underneath the paper you get
two piles of cornmeal. That is emphatically NOT what we see when we actually do the
double slit experiment with light!
The Single Slit Experiment
This is another diffraction pattern, evidence of the wave nature of light, made by passing
a laser pen beam through a single slit. I have a device with a very thin, straight slit that
can do this.
Dispersion with Laser Pens
This is done by directing beams from parallel laser pens into an aquarium filled with
water and diluted skim milk. The beams, if of different colors, are not parallel after
refraction by the air/water boundary. This demonstration can be extended to what
happens to sunlight passing through raindrops and is the basic physical effect behind
the rainbow.
Total Internal Reflection
Total internal reflection occurs when light encounters a boundary between two
transparent materials and is completely reflected by the boundary. This effect is the
basis for fiber optics. The demonstration can show that this effect occurs for only some
angles and only with light traveling from water to air and never the other way. The
physical basis for the demonstration can be a water filled aquarium or a sculpted piece
of jello.
Fermat’s Principle of Least Time
A laser pen and a water tank show that light travels from point A to point B by the
quickest pathway. Light only travels by the shortest pathway when the shortest
pathways is also the quickest.
Charge Polarization in an Electrically Neutral Object
This is why electrically neutral objects are attracted to object with a net electric charge.
Various objects can be used to show this but metal coated glass Christmas ornaments
are very good.
Franklin’s Bells
This shows the concept of electric charges with the same sign repelling each other,
resulting in a tendency to dissipate. This also shows the function of an electric ground.
Physically the demonstration involves leaching a static electric charge from the glass of
an old fashioned cathode ray tube TV. As the charge dissipates it runs through a series
of two bells and a clapper (made of a Christmas ornament) and rings the bells.
The Northern Lights and Van Allan Radiation Belts
This is done by projecting one pole of a magnetic field from a strong neodymium
magnet into an old fashioned black and white cathode ray tube TV screen. The result is
a donut of black with a bright center. The donut of black occurs where the magnetic field
deflects the electron beam inside the tube so that those areas of the screen receive
none and effectively represents the radiation shield provided by the Earth’s magnetic
field and confinement of charged particles elsewhere in the Van Allen radiation belts.
The bright spot represents the spiraling of charged particles down toward the magnetic
pole. This happens on the Earth for exactly the same reason and results in the northern
and southern light. It’s fun after that to show internet video of the shuttle flying through
the northern lights and/or of the northern and southern lights on different planets.
Magnetic Levitation
This is done with a magnetic model globe of the Earth interacting with a nearby
electromagnet with a feedback effect to overcome unstable equilibrium. The basic
structure of the device internally can partially be deduced by students if they are allowed
to examine and experiment with it.
Wireless Transmission of Energy
This is the transmission of electrical energy between two systems (coils) that are not
physically connected to each other. It’s easy to show that a common magnetic core to
the coils strongly enhances the effect. Most students don’t know that this is basically a
transformer and happens all the time (like in the power plugs of their phones and
laptops).
Wave Quantization by Confinement
…or why microwave ovens have hot and cold spots that can’t be gotten rid of. Confining
any wave results in quantization: only waves of certain wavelengths and energies can
exist in the confinement. In this case we have microwaves confined in a microwave
oven. If you microwave a layer of marshmallows in the oven melting occurs at the
antinodes of the waves (hot spots). You can use the spacing of these spots to calculate
the wavelength of the microwaves.
I can generalize this concept to the confinement of electrons around an atomic nucleus.
Since electrons have a wave nature this confinement quantizes the electron energies.
These are the electron orbitals. I then move on to a direct consequence of this
quantization: emission spectra.
Direct viewing of Spectral Emission Lines
The school has some equipment to do this and I have some diffraction gratings for
viewing. The spectral lines are very bright and colorful. I have my students use the line
coloring and spacing to identify the substances generating the emission spectra!
Inertia Demonstration Using Balls
A basketball, golf ball and several bowling balls show that inertia is a resistance to
acceleration and an intrinsic property of mass.
Broken Nose Bowling Ball Pendulum
I have a bowling ball that I suspend by a chain. I then draw the bowling ball away from
the vertical, hold it still a quarter inch from my nose and release it. I do not move. The
ball returns on its swing and stops just short of my nose. The point is that unless energy
is added to the system the ball cannot swing back far enough to hit my nose. Then I
have a student shove the ball as it swings, giving it an input of energy. I move out of the
way this time.
Newton’s Third Law with Office Chairs
This involves two students in rolling office chairs. With their feet off the floor there is no
way that they can push on each other without both moving.
Conservation of Angular Momentum Using an Office Chair
I spin in a rotating office chair while holding dumbells in my hands. As I move the
dumbells closer to or farther from me my rotation rate changes. This my equivalent of a
.
Conservation of Angular Momentum using a Lazy Susan
This involves standing on a laboratory version of the familiar kitchen device. If you twist
your arms in one direction the lower part of your body must twist the other way. This is a
consequence of The Conservation of Angular Momentum. It’s very odd to feel your
lower body moving without consciously willing the movement. Students can actually
FEEL the Law of Conservation of Angular Momentum!
Explanation of how to Build an Inertial Guidance System
This involves a demonstration of the action of small gyroscopes. The gyroscopes will
resist any change in their angular momentum vectors and this resistance can be used to
make an inertial guidance system.
Why Bicycles and Motorcycles are more stable at Higher Speeds
Hold a rotating bike wheel and find out!
Simple Demonstration of The First and Second Laws of Thermodynamics
All done using just a golf ball.
How we know Potential Energy Exists
Also done using just a golf ball!
The Bernoulli Effect Using a Ping Pong Ball
This is done most visibly with a ping pong ball and a hand held hair dryer but I like to
use the ping pong ball and my own breath. The Bernoulli effect is the major reasons that
airplanes fly.
The Bernoulli Effect Using Cans
Blow between two empty cans placed near each other on their curved sides and the
cans roll together. This is also the Bernoulli Effect.
Explaining Why Kinetic Energy is not Conserved in Inelastic Collisions
The easiest way to do this is to throw a ball of clay against a wall. The clay changes
shape during the collision, which requires some of the kinetic energy of the clay. Energy
dissipated in changing the shape of something cannot also stay kinetic energy (a
consequence of the Law of Conservation of Energy).
If the impact of the clay makes a loud noise, that and the sight of the teacher actually
throwing something across the room will wake up anyone not paying attention.
Showing the Difference between Elastic and Inelastic Collisions
This can be done with dropping simultaneously and from the same height a golf ball and
a hackysack ball. One will bounce a lot and the other just thuds without bouncing much.
Demonstrating Faraday’s Law, Ampere’s Law and Lenz’s Law 1
This can be done by dropping a magnet through the center hole of a roll of aluminum
foil. Try it, it’s fun. And there’s one heck of a lot of physics in that simple demonstration.
Demonstrating Faraday’s Law, Ampere’s Law and Lenz’s Law 2
This involves suspending a loop of copper pipe or small piece of aluminum foil from a
thread. A magnet moving relative to these objects can exert magnetic forces on these
otherwise non-magnetic materials and move them. Again, a great deal of physics here.
Demonstrating Archimede’s Principle 1
This involves immersing two full apparently identical soda cans in a tank of water. One
floats and the other does not. One of the cans contains diet soda the other sugared
soda. The addition of sugar to the solution in one of the cans changes its density
relative to water and makes the difference between floating and not floating.
Demonstrating Archimede’s Principle 2
This involves adding 5 liquids to a graduated cylinder that then form layers in order of
their densities. Making the liquids different colors adds to the effect. I usually use corn
syrup, glycerin, water, vegetable oil and isopropyl alcohol. It’s pretty and informative. It’s
also a mess to get rid of.
Electric Cake
Cake batter actually cooks into a cake when two electrodes hooked to the wall outlet
are immersed in the batter. This is a graphic demonstration of the relationship between
resistance, voltage and current (Ohm’s Law) and what does and doesn’t change when
an electric circuit loses energy to the environment. I make measurements of what is
going on in the cake with a multimeter while it cooks. I actually eat some of the cake at
the end of class. Physics you can eat!
Simultaneous Demonstration of Conservation of Momentum and Kinetic Energy
This uses the familiar linear set of suspended metal ball bearings that bounce off each
other (Newton’s Cradle). The patterns of bouncing are consistent only with both these
things being conserved and you can show this to the students. It’s a good example of
how conservation laws dictate the behavior of a system.
Conservation of Mechanical Energy
Release a marble in a hemispherical bowl. It’s rolling back and forth is a good example
of the Conservation of Mechanical Energy. A pendulum does much the same thing. This
is easily generalized to explain why an object in a noncircular orbit cannot have a
constant speed. The connection of such a simple system with something as grand as
planetary motion is meant to stimulate an interest in the subject matter.
Stable and Unstable Equilibrium
A bowl that is essentially a hemisphere can be used to show the difference. With stable
equilibrium there is a restoring force that makes the behavior of the system stable and
repetitive. Unstable equilibrium occurs when the slightest disturbance will result in a
profound change in the system because no restoring force exists.
A marble rolling back and forth in the bowl will show a restoring force and stable
equilibrium. The same marble when placed on the top of the inverted bowl must be
placed perfectly to stay there. Any slight disturbance will permanently disrupt the system
(the marble rolls off the bowl and doesn’t come back).
The Basis for the Electric Motor
This is two demonstrations. The first shows that an electric current in a wire creates a
magnetic field around the wire (unless it is coaxial). The second shows that a magnetic
field not created by such a current but imposed from the outside can exert a force on a
wire carrying an electric current. These two effects form the basis for the electric motor.
Why the Acceleration of Electric Charges has to result in the Emission of
Electromagnetic Waves
This is done using me and a student. I’m the electric charge and accelerate the charge
by moving myself back and forth relative to the student. The student is the detector of
electric and magnetic fields, the intensity of which change as I move. Once you have
done experiments establishing the facts that the movement of electric charges cause
magnetic fields and that both magnetic and electric fields weaken with distance from the
charge it’s easy to see that some sort of disturbance must pass between me and the
student. We call those disturbances radio waves.