DEMONSTRATIONS UPDATE SPRING 2008

PHYSICS IS AN EXPERIMENTAL SCIENCE

DON'T JUST TALK ABOUT IT DO SOMETHING

Most of the demonstrations available are described in the Demonstration Page section of the Physics Department web site ( www.physics.auburn.edu, Introductory Courses menu). Some new and changed demonstrations are described below. Astronomy and Modern Physics sections have been added since site was created. During the summer and fall of 2006 a large number of changes were made to mechanics, E&M, fluids, and thermodynamics sections. The other sections will be changed later. The demonstration part of the department web site has been redone using a program called Joomla!.

CHANGES TO DEMONSTRATIONS ON WEB SITE AND TO EQUIPMENT

RECENT CHANGES

1. Euler disk available. As it spins it slowly falls over so gravitational potential energy becomes rotational kinetic energy and keeps it spinning longer.

2. New device to demonstrate pressure versus volume relation for ideal gas.

3. Green plug in laser and 3 times brighter red laser available.

4. Device that produces 5 laser beams for use in ray tracing available.

5. Water wheel device to produce electricity now available.

6. New vibrator for use with standing wave demonstration. Use longer string setup on front desk.

7. New Faraday cage.

8. Smaller and easier to use Tesla coil.

9. Small torch to heat ball and rod used in effect of heat on length demonstrations.

10. New device to show conversion of gravitational PE to rotary KE. Position of masses can be varied to show effect on rate of rotation.

11. New device to demonstrate conservation of angular momentum. Shows why a helicopter needs tail rotor.

19. Motor driven model of solar system available for astronomy class or lab.

Older Changes You May Have Missed

NEW DEMONSTRATIONS

MECHANICS

1. 1N30.50 LINEAR MOMENTUM:COLLISIONS New device for discussing momentum conservation in collisions. If sharp point hits board it will wobble but not fall over. If the sharp point is removed so rubber ball hits board it is knocked over easily. Why does it fall over even though moving object has less mass hence less momentum?
2. 1F10.20 NEWTON'S FIRST LAW:INERTIA VERSUS WEIGHT Have students come up to front desk and lift and move horizontally what looks like a regular Pepsi can. It is filled with lead so a noticeable force is needed to move it horizontally as well as lift it. Compare to empty can and can filled with Pepsi.
3. 1Q40.05 ROTATIONAL DYNAMICS:ANGULAR MOMENTUM This demo simulates what happens when a helicoper takes off. A fan starts turning. The device has acquired angular momentum using an internal power supply. To compensate the entire device starts spinning in opposite direction. If you tilt the fan you can show how a helicopter moves foward also.
4. 1Q50.15 ROTATIONAL MECHANICS: PRECESSION. This demo involve device called Euler's Disk. This can be used as a small scale demonstration of precession. Unlike the large bicycle demo of precession, the disk slowly falls over. It thus also demonstrates conversion of gravitational potential energy to rotational kinectic enegy. The frequency of the sound you hear increases just before disk comes to halt.
5. 1Q50.21 ROTATIONAL MECHANICS: PRECESSION. Another way of demonstrating precession is to suspend a spinning wheel using a rope attached to one end of a rod passing through center of wheel. Practice this one before class.
6. 1D60.35 MOTION IN 2 DIMENSIONS: PROJECTILE MOTION A device is available to show how range varies with angle. Projectile falls on desk. Put something on desk to mark where projectile lands for different angles.
7. 1Q20.50NEWTON'S SECOND LAW: COMPLEX SYSTEMS A device is available to demonstrate the standard textbook problem that shows that a falling object can have an acceleration > g. This is called the hinged stick device. It is related to falling chimney problem.
8. 1H10.15 NEWTON'S THIRD LAW As a way of demonstrating action-reaction we have a small boat that shoots water out a tube on the back. Use it in one of the fishtanks used for optics demos. Stand clear once you start boat. Have towel ready.
9. 1Q40.40 ROTATIONAL DYNAMICS:ANGULAR MOMENTUM Use train on turntable to illustrate conservation of angular momentum. Train goes one way, turntable rotates in opposite direction.
10. 1R40 PROPERTIES OF MATTER: COEFFICIENT OF RESTITUTION Bounce/No Bounce: Balls look the same. One bounces. One does not. Use when talking about coefficient of restitution or energy conversion (PE>KE> heat and sound).

FLUIDS

1. As an attention getting but messy way of introducing fluids try this. Put a warm 2 liter bottle of diet Coke in the sink. Add 2 pieces of Mentos candy. Get out of the way. The contents will shoot up in the air. You may want to move students away from sink. Have a towel available. This is not a chemical reaction.The carbon dioxide rapidly leaves the liquid. Physicists still debating surface tension reduction versus nucleation sites. Bring your own diet Coke. Mentos in stock.
2. 2B20.50 STATICS OF FLUIDS:STATIC PRESSURE Pascal's Principle device. Push on plunger. Pressure will be transmitted throughout fluid causing it to squirt out holes. Safety Hazard: angry wet students.
3. 2B40.54 STATICS OF FLUIDS: DENSITY & BUOYANCY What determines whether an object sinks or floats? As a visual aid put a can of Classic Coke and a can of Diet Coke in one of our "fish tanks". The Classic Coke can will sink. The Diet Coke can will float. Pepsi version also available.
4. 2B40.71 STATICS OF FLUIDS:DENSITY & BUOYANCY Demo has three liquids with different densities and objects of different densities floating at different levels. Assembled as needed.
5. 2B40.59 STATICS OF FLUIDS:DENSITY & BUOYANCY Another way to demonstrate connection between density and floating. Color hot water with yellow food coloring. Color cold water with blue food coloring. Fill cylinder about 2/3 full with cold water. Slowly add hot water until full. The top half will turn green where the water mixes. The bottom half stays blue. The warm mixture floats on the cold bottom layer.
6. 2C20.45 DYNAMICS OF FLUIDS: BERNOULLI PRINCIPLE . Hang two bowling balls from metal rod so they are a few inches apart. Use a leaf blower to blow air between them. Which way will they move?
7. 2C50.10 DYNAMICS OF FLUIDS: VORTEX Use device to produce smoke rings. The ring has a low pressure area at the center. Compare to hurricanes. Useful as attention getting device.

THERMODYNAMICS

1.4B30.23 HEAT: CONDUCTION Put ice cubes on two nearly identical blocks. One will melt much faster. Talk about Q=mc(delta T), Q=mL, and conductivity. One block is aluminum painted black to look like other material. Other material has low heat conductivity.
2. 4B40.10 HEAT : RADIATION Use metal mirrors with about one foot diameter. Place heating coil about 9-10 cm from concave mirror. Use jack stand to center coil. Place second mirror about 1 meter from first mirror. Use rods and clamps to place match about 9 -10 cm from second mirror. Adjust mirrors and match so orange light relected by second mirror shines on the match head. You may have to turn out lights near setup to see light on matchhead. The match will start smoking and then burst into flame. You may want to turn out all light when you see matchhead start smoking.
3. 4A30.12 THERMAL PROPERTIES:EXPANSION Expanding wire demo. Length of wire increases when heated. Pointer moves along scale.
4. 4B60.15 HEAT AND FIRST LAW:CONVERSION OF K.E. TO HEAT. Put a piece of paper over large metal ball and hit it with the other ball. Enough kinetic energy will be converted to heat to burn a hole in paper. In smaller classes do several times and pass paper around so students can smell that paper is burned not just torn.
5. 4B20.25 HEAT: CONVECTION Symmtery Breaking and Convection. If lit candle is covered with a long tube it will go out. All the oxygen near candle is used up. Rising hot gases prevent more air from coming in. Put a divider in midddle of tube and try again. There is so much air flow it blows flame around. Some small random difference converts symmetric situation into one with hot gases going up one side and fresh air going down other side of tube.
6. 4F10.46 ENTROPY Exploding fuel demo ( like in car engine). A small amount of methanol is placed in a plastic bottle. Put on top and swirl around to fill space with vapor. Replace screw on cap with cork. Use hand held tesla coil to apply high voltage to screw in side of bottle. Blue flame and loud explosion occur. Cork heads toward ceiling. Wear eye protection. Try this out ahead of time so you will know what to expect.
7. 4B10.20 HEAT: HEAT CAPACITY See color mixing demo under fluids. Serves as example of what happens when you bring objects at different temperatures in contact and as example of irreversable process.
8. 4B30.50 HEAT: CONDUCTIVITY Liquid nitrogen cannon: Besides intended use, also useful in discussing frost/dew formation or as example of conduction in metal. One day advance notice needed or bring your own LN. 9.
9. 4B40.40 HEAT:RADIATION Demonstrate that good absorbers are good emitters. Put hot water in a silver can and a blck can. Record temperature. Keep checking and recording temperature. The black can should cool faster.
10. 4D20.11 KINETIC THEORY: RADIOMETER. The idea that dark surfaces are better emitters than light surfaces can also be demonstrated using the radiometer. Use the hot air blower to heat it until it is spinning rapidly. Let it cool off. It will come to a stop and slowly rotate in the reverse direction.

ELECTRICITY AND MAGNETISM

1. 5C30.31 CAPACITANCE: TIME CONSTANT Variation of capacitor and bulb uses 5 bulbs to visually show how changing resistance affects decay time. A capacitor is charged from 6V battery. It is then discharged through light bulb(s).
2. 5F30.20 RC CIRCUITS: TIME CONSTANT An oscilloscope version of capacitor & bulb is available. Shows exponential charging or discharging curve. Also can be used with inductor instead of capacitor. At least 1 day notice needed to assemble and test
3. 5C10.21 CAPACITANCE: EFFECT OF SPACING The change in capacitance due to changing plate separation can be demonstrated using digital multimeter that measures capacitance. The output can be sent to a computer and displayed on movie screen.
4. 5H20.05 MAGNETIC FIELDS & FORCE:FORCES ON MAGNETS The effect of the Earth's magnetic field on a magnet can be demonstrated by rolling a small but strong disc shaped magnet down an incline. Instead of rolling straight down the magnet will curve to left or right depending on orientation.
5. 5C30.35 CAPACITANCE: CHARGING CAPACITOR. Hook a generator to the 1 farad capacitor(5v limit). Note that as you turn the handle it becomes easier as the capacitor charges up. The rate at which the voltage changes is reduced. If you let go, the handle will continue to turn. Ask class to explain why torque needed is reduced, why charging rate goes down, why handle turns, and which way will it turn.. Device to visually demonstrate current flow could be used with this demonstration.
6. 5B10.45 ELECTRIC FIELD & POTENTIAL A model of a molecule lining up in an electric field is available. Two balls on the ends of a rod are placed between plates of a capacitor. The capacitor is charged using a Van de Graff generator. The rod is initially placed at right angles to field. Can be used to explain why charged rod bends water and grass seed floating in oil line up with field.
7. 5B10.35 ELECTRIC FIELD & POTENTIAL A variation on this idea of initially uncharged objects being attracted by charged objects involves having a metal ball bounce back and forth between plates connected to ground and sphere of Van de Graff generator. One version of this is called Ben Franklin's bells.
8. 5H30.56 MAGNETIC FORCES: FORCES ON CURRENT Besides bending water with a charged rod you can make water move using a magnet. At least 1 day notice needed to assemble and test. Aluminum foil is placed aroung the edge of a container of salt water. It is placed between the poles of a magnet. An electrode is placed in the center. A car battery is connected to the electrode and the aluminum foil. The magnet exerts a force on the current between the foil and center electrode. As a side effect electrolyis also occurs.
9. 5A20.15 ELECTROSTATICS: COULOMB'S LAW A device is availble to demonstrate the force between charged objects. At least 1 day notice needed to assemble and test. One metal plate is connected to ground. Another plate connected to a spring is suspended several centimeters above grounded plate. This plate is connected to sphere of Van de Graff. The plates will acquire opposite charges. The one on spring will move down until it touches other plate and charge is neutalized. The spring will then pull the plates apart.
10. 5H20.22 MAGNETIC FORCES: FORCES ON MAGNETS Objects suspended using static electric or magnetic fields are usually considered examples of unstable equilibrium. We have a device that uses two plates of diamagnetic material to stabilize a small magnet levitated using a magnetic field.
11. 5G30.10 MAGNETIC MATERIALS: DIAMAGNETISM As another example of diamagnetism grapes are placed on opposite ends of a small rod. The rod is suspended using thread. A strong magnet brought near a grape will repel it causing the rod to rotate. Bring your own grapes.
12. 5N30.11 ELECTROMAGNETIC RADIATION: SPECTRUM. Instead of using projector as light source to produce spectrum with prism use the overhead projector. Cover most of the plate with paper leaving a narrow slit. Hold prism or grating nears lens of projector.
13. 5D10.40 RESISTANCE:CHARACTERISTICS The small bed of nails can be used as model of electrical resistance. Use small ball to represent electron. Nails represent atoms.
14. 5L10.10 AC CIRCUITS:IMPEDANCE Show the effect of inductance on "AC resistance" (impedance). A flashilght bulb is connected in series with the jumping ring coil . A Variac is used to supply ~ 6v AC. The brightness of the bulb will vary as you move the iron core in and out of the coil.
15. 5K40.41 ELECTROMAGNETIC INDUCTION: MOTOR & GENERATOR Bare bones motor/generator. Magnetic field can be provided by large coils or large permanent magnet. When used with op amp circuit you can generate currrent using Earth's magnetic field.
16. 5K40.71 ELECTROMAGNETIC INDUCTION: MOTOR ACTS AS GENERATOR Attach an AC voltmeter to DC Motor. The AC meter will not respond to DC current used to operate motor. The AC meter will show a rising voltage (pulsating DC) as the motor speed increase.
17. 5K10.15 ELECTROMAGNETIC INDUCTION: DEMONSTRATE EMF=BLV Attach wire to rods. Place large magnet so wire is between poles. Attach cable to each end of wire and connect to oscilloscope. Pull on wire and let go. A distorted and damped sine wave will appear on the oscilloscope. Some trial and error need to adjust volt/div and time/div controls.Advance notice needed.
18. 5K40.15 ELECTROMAGNETIC INDUCTION: FARADAY'S MOTOR One of the small but strong magnets is placed in the center of a pool of mercury. A rod is suspended so one end is in the mercury. Aluminun foil is placed aroung the edge of the container. A DC power supply is connected to the foil and upper end of rod. The rod will move due to force exterted by magnet on current. Assembled as needed.
19. 5K10.25 ELECTROMAGNETIC INDUCTION: EMF DUE TO CHANGING FLUX . A flashlight is available that uses a capacitor charged up by moving a magnet back and forth through a coil instead of batteries. Uses the idea that an EMF is induced in the coil by changing magnetic field (one of Faraday's contributions to E&M).
20. 5A30.10 ELECTROSTATICS: CONDUCTORS VS INSULATORS. Use the Van de Graff to illustrate the difference between conductors and insulators. Put aluminun foil on base of one of the devices with red or yellow threads. Put the other one on top of the Van de Graff and note how long it takes to charge up and threads to stick out. Repeat with the one with foil.

OPTICS

1. 6A60.20 RAY TRACING: THICK LENS IN WATER Instead of filling the air with chalk dust to show laser beam, put a thick lens under water. Add a small amount of non-dairy creamer to make laser beam visible. Why thick lens? What happens if "lens" is filled with air rather than being solid glass?
2. 6A40.45 GEOMETRIC OPTICS: INDEX OF REFRACTION A mirage like effect can be demonstrated by shining a laser through a water-sugar mixture. On top is water only. On bottom is water with a large amount of sugar in it. A laser beam pointed slightly upwards will be bent downwards. Advance notice needed to prepare solution.
3. 6A44.41 GEOMETRIC OPTICS: TOTAL INTERNAL REFLECTION. Shine laser beam from the brighter red laser on edge of notch on one end of cylinder. Internal reflection will cause the beam to spiral around the cylinder.
4. 6A40.30 GEOMETRIC OPTICS: INDEX OF REFRACTION Now you see it. Now you don't. Pour some Wesson Oil into a clear container. Put a pyrex test tube in the oil. Fill the test tube partly with Wesson Oil. The part that is filled with Wesson Oil will seem to disappear. Another version using anisole and an eyedropper is also available.
5. 6D20.11 INTERFERENCE: GRATING Shine red and green laser through diffraction grating at same time to show how pattern vaires with wavelength
6. 6A40.47 GEOMETRIC OPTICS: REFRACTION. Demonstrate " twinkle twinkle little star" by putting slide of constellation in slide projector and adjusting so beam passes just over top of hot hotplate.

NEW SECTION ADDED TO DEMONSTRATION PAGES

MODERN PHYSICS

The following demonstrations are now available in the Modern Physics category.

Quantum Effects: Photoelectric effect using phototube, photelectric effect using solar cell, vibrating ring to similate electron orbit
Atomic Physics: Assorted element emission lines, sodium emission lines, molecular emission lines (carbon dioxide & water), broadband absorption
Nuclear Physics: Radioactive sources, shielding, probability,cosmic rays,half-life
Relativity: Coil & Magnet, Frames of Reference