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ASTR 100

  • G4-03: RIPPLE TANK - DOPPLER EFFECT

    G4-03
    Show how wave fronts crowd together in front of and spread out behind a moving source.
    The single point source can be moved by rotating the support arm on a lazy susan. Moving the source uniformly in one direction demonstrates the Doppler effect in a clear and understandable way.
    OS7

    g4-03a g4-03b

  • H1-01 BELL IN VACUUM

    H1-01
    Demonstrates sound wave requirement for a medium

    An alarm-style electric bell is mounted inside a large glass bell jar, with external switches to control both the bell and the pump. This enables the instructor to compare the propagation of sound and light.

    Start the bell, then pump the air out of the jar. Air pressure in the jar is read by the large gauge. As the air is removed, the sound intensity decreases, ultimately to nearly zero. Turn off the vacuum pump when the jar is evacuated and crack the valve open, allowing air to re-enter the jar. As the pressure increases the sound of the bell comes back, but without the noise of the pump.

    Engagement Suggestion
    • Consider asking the students to make predictions before each step - how will removing the air change what they hear? What they see? What will happen as the air returns?
    • Compare this to videos the see of people working in the vacuum of space, in real life and in the movies. What do you see and hear in real life? How is this presented in fiction, and why?
    Background
    There are subtleties to this effect. The pump is not creating a true vacuum within the chamber. The vast majority of the air has been removed, reducing the environment’s ability to transmit sound; but the other (perhaps more important) effect in play is the difference in density between the interior of the chamber and the glass and the external atmosphere; this creates a major change in impedance, causing what little sound can be transmitted within the chamber to reflect back. Also, off course, the bell is not floating in free space, and some vibrations can always be transmitted through the supports and wires.

    For small groups, also consider H1-04, a more portable version of this demonstration.
    FS1

  • H1-02 SPEAKER AND CANDLE

    H1-02
    Demontrates longitudinal behavior of sound waves
    A lighted candle is placed directly in front of the center of a large loudspeaker, which is operating in the 10 Hertz range. The motion of the candle flame is longitudinal, following the motion of the air, illustrating the longitudinal nature of sound waves.

    With a bit of exploration, one can find resonances in the system that produce the most dramatic flame displacement. Consider having students make predictions about how different waveforms will make the flame respond differently
    OS5, ME2

  • H2-41 DOPPLER BALL

    H2-41
    Demonstrates Doppler effect

    An electronic device making a loud squeal is turned on and placed inside a foam ball. The ball is then zipped inside a cloth cover hooked to the end of a cord, and whirled about the instructor's head or carefully tossed from person to person. The Doppler effect can easily be heard throughout even a large room.
    Engagement Suggestion:
    • Challenge students to describe other circumstances where they have heard this phenomenon
    Background:

    This is a classic illustration of the Doppler Effect. When a wave source is in motion, the wavelength of the emitted waves is observed to change by an observer along its direction of motion.

    It can be useful to present this in conjunction with an animation or simulation, to illustrate the effect visually; see the relevant page of our Directory of Simulations.
    H2

  • H2-42 DOPPLER EFFECT - TUNING FORK ON STRING

    H2-42
    Demonstrates Doppler effect

    A tuning fork is struck to activate the "clang tone" and whirled about the instructor's head on a string. The Doppler effect can easily be heard in a small classroom or a reasonably quiet lecture hall.
    Engagement Suggestion
    • Encourage students to listen closely to how the pitch changes, and compare it to other similar sounds. Where else do they experience this effect?
    Background
    As the source of the sound waves moves through the air, the wavefronts in the direction of motion are compressed, while the wavefronts in the opposite direction are extended, changing the pitch we hear. Because the fork is rotating, this causes a repeating pattern as the pitch is first higher, then lower, than the natural pitch of the tuning fork.
    H2a

  • I1-19: LAVA LAMP

    I1-19
    Demonstrate differential thermal expansion between two liquids, and to take us all back to the 1960s.
    Globs of petrolium-based fluids expand at a different rate from the water bath in which they are placed. After the mixture gets up to its equilibrium temperature differential expansion occurs, leading to the rising and falling of the globs as they become more or less dense than the liquid bath. It's also kind of pretty.
    I1

  • I1-51: RUBBER AT LN TEMPERATURE

    I1-51
    Demonstrate how a normally elastic material at room temperature becomes rigid at very low temperatures.
    Dip a rubber sample into the liquid nitrogen with the tongs, then place it on a wooden "anvil" and hit it with a hammer to break it. Show the students in the audience how the material's property change with temperature.
    I0, I1

  • I1-61: DUST EXPLOSION

    I1-61
    Produce a dust explosion.
    A rounded tablespoon of lycopodium powder placed in the funnel is blown upward by blowing into the end of the rubber tube, which can be stretched out. When the cloud of powder reaches a burning candle flame, on the top mount, it ignites readily to create a dust explosion. This is a very dramatic effect.
    I1, I0, C2, FS2

    i1-61ai1-61b

  • I1-63: HYDROGEN EXPLOSION

    I1-63
    Produce a hydrogen explosion

    A balloon filled with hydrogen is tethered about six feet above head level. The burning match on a stick is positioned under the balloon, creating the hydrogen explosion.
    Engagement Suggestion
    • One option for presenting this would be to compare the behaviour of two different balloons, hydrogen and helium. You can tell students what is in each balloon and have them make a prediction about what each will do, or show the demonstration first and then have students analyze why the results were different.
    I1, I0, FS1

    I1-63B

  • I2-04 WIEN'S LAW OF THERMAL RADIATION

    I2-04
    Shows that higher temperature blackbodies radiate with shorter wavelengths

    A variable transformer, or Variac, is connected to two identical incandescent light bulbs in parallel. These bulbs are viewed behind red and blue filters respectively. As the voltage is increased by the variac, the lights glow more brightly, and more light is seen through the blue filter relative to that of the red filter. Very little or no blue is seen at low voltages, whereas red is seen to be emitted even at very low voltages.

    Engagement Suggestion:
    • Ask students to compare this to other phenomena that emit light. Where else do you se this change of color with temperature?
    Background:

    Wilhelm Wien postulated in the 1890s that the power curve of blackbody radiation from an object could be computed from its temperature. His original calculations, obviously, did not take quantization into account; in modern practice, the revised calculations are still commonly referred to as Wien's Law.

    Note that this apparatus only works with incandescent lightbulbs. Fluorescent and LED bulbs do not produce their primary light through thermal excitation, and thus don't produce the same kind of blackbody spectrum.
    I2, PS1

  • I4-17: AIR BALLOON ON LIQUID NITROGEN

    I4-17
    Demonstrate dramatically that the volume of vapor is greater than the volume of the same amount of liquid.
    An air balloon is held on top of a liquid nitrogen bath. The volume of the air balloon decreases for two reasons: first, the volume of the gas shrinks according to Charles' law, and second, some of the air changes to liquid and shrinks considerably. Liquid nitrogen will readily cause oxygen to liquify, and even liquify some of the nitrogen in the balloon.
    I0

    i4-17a

  • I4-51: SUBLIMATION OF DRY ICE - PROJECTION

    I4-51
    Demonstrate sublimation of carbon dioxide (dry ice) from a solid into a gas.
    Place a chunk of dry ice on the plastic sheet, on an overhead projector if desired. As the dry ice evaporates (evaporation sublimation) it becomes smaller but leaves no residue.
    I4, I0

  • I5-12: ADIABATIC EXPANSION OF AIR - FOG IN BOTTLE

    I5-12
    Demonstrate adiabatic cooling of air
    A bottle containing a small amount of water is sealed by a stopper. A tube passes through the stopper and is attached to a bicycle tire pump which is pumped to pressurize the bottle. When the pressure rises to a sufficient level it blows the stopper off the bottle, allowing the air to expand adiabatically and cool. The cooling process condenses water vapor in the bottle, producing fog. If the stopper is quickly replaced and the pressure in the bottle increased, the air becomes warmer and the fog disappears. A small lamp illuminates the bottle to make the fog very visible, even in a large room.
    I7, LS2

  • I5-15: ADIABATIC EXPANSION OF CARBON DIOXIDE

    I5-15
    Illustrate adiabatic cooling by producing dry ice
    Carbon dioxide, leaked slowly out of the fire extinguisher onto a black felt cloth, produces dry ice, which can be easily seen. Adiabatic expansion and cooling occur when the CO2 gas comes out of the nozzle under high pressure and expands in the atmosphere. Enough is produced to pass the cloth around the class so that students can feel that it is actually cold. This experiment is a bit more complicated than simple adiabatic expansion. The carbon dioxide actually exists in the fire extinguisher as a liquid, so that much of the cooling is due to the evaporation of the liquid CO2 before it is ejected from the nozzle.
    FS1

  • I5-21: HEATING AIR BY COMPRESSION

    I5-21
    Demonstrate heating air by compression.
    A few pumps of the tire pump into a mostly filled basketball warms the end of the pump noticeably. You can show that this is not due to friction by moving the pump handle back and forth in the same style with no load. You can simultaneously demonstrate cooling by expansion by observing that while the pump and the needle get rather warm, the air inside the ball actually cools.
    I5

  • I5-22 FIRE SYRINGE

    I5-22
    Demonstrates heating air by compression

    This demonstration consists of a transparent cylinder with a flared base, and a plunger that can be pushed into it. A small (very small) piece of cotton is pushed into the bottom of the tube using the wire provided, and the plunger is sealed into the tube. The plunger is pushed down sharply, compressing and thereby heating the air within. The temperature rises high enough to ignite the cotton with a flash, which can be readily seen through the plastic tube.
    Engagement Suggestion
    • Consider inviting a volunteer from the audience to try the demonstration. This will require careful supervision, but is safe. Just ensure that the syringe isn't knocked off the table by an overenthusiastic student!
    • This demonstration works best with a very small amount of cotton to ignite, no more than a few millimeters at most. Consider showing the device with different amounts of cotton, and how the results change. Encourage students to discuss reasons for this.
    Background
    This demonstration illustrates that an essentially fixed mass of air will increase in temperature when its volume is reduced, i.e. it is heated when compressed. The fire syringe is a simple piston, and can be used to introduce a discussion of the use of pistons in engines.

    Consider using this demonstration in conjunction with both other thermodynamics demonstrations from section I5, and relating it back to general gas behaviour with demonstrations from section I3.
    I5

  • I6-01 GAS PRESSURE - MODEL

    I6-01
    Illustrates the molecular nature of gas pressure
    A vibrator motor is activated causing chaotic motion of a group of ball bearings in a clear plastic container. The upward motion of the ball bearings pushes a black plastic plate upward, indicating the upward force of "air pressure" on the plate. Increasing the speed of the motor by turning up the variac increases the average speed of the balls and pushes the plate up further, modeling a greater pressure.
    I6, PW1

  • J1-06: FUN-FLY-STICK

    J1-06
    Demonstrates electrostatic fundamentals
    This is a battery operated static electricity generator that allows you to float tinsel shapes above the electrically charged stick. Since like charges repel each other, the negatively charged tinsel floats above the negatively charged stick.
    J1b

  • J1-24 ELECTROSTATIC HAIR RAISING

    J1-24
    Demonstrates electrostatic repulsion
    While standing on a large styrofoam insulating block, touch your hands to the top of the Van de Graaff dome, then have someone turn it on. The fact that your hair stands on end is a result of the repulsion between charges of the same sign that collect on your hair.
    J1a, OS2

  • J1-26 VAN DE GRAAFF - REPULSION OF PIE PANS

    J1-26
    Demonstrates electrostatic repulsion

    A group of aluminum pie pans is placed on top of the Van de Graaff dome and the Van de Graaff is turned on. The pie pans are pushed off the top of the dome one at a time by the electrostatic repulsion. Use this as a way to argue that electrostatic forces might be stronger than gravitational forces.

    Engagement Suggestion:
    • Before turning the generator on, encourage students to predict what is going to happen. Challenge them to explain their hypotheses in terms of what they have learned about the behaviour of electrical charge.
    • Feel free to invite students to collect the scattered pans, but remind them not to get close to the Van de Graaff while it is turned on.
    J1a