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PHYS141

  • G1-11 COMPARISON OF SHM AND UCM

    G1-11
    Demonstrates the relationship between simple harmonic motion and uniform circular motion.
    Turning a crank on the rear of the apparatus causes the center ball to move in circular motion around a 30cm diameter orbit, while the ball on top executes simple harmonic motion. It can be seen that SHM is the projection of UCM. This device can also be used to discuss the concept of degrees of motion in SHM by comparison with the reference circle.

  • G1-14 PENDULA WITH DIFFERENT MASSES

    G1-14
    Demonstrates independence of a simple pendulum's period with mass of the bob.
    Four geometrically identical pendula have bobs made from lead, brass, stainless steel, and aluminum, respectively. Their periods are the same.
    FS2

  • G1-34: AIR TRACK - SIMPLE HARMONIC MOTION

    G1-34
    Demonstrate simple harmonic motion of a mass held by two springs.
    The center (moveable) glider, connected by springs to two fixed gliders (taped to air track), executes SHM about its equilibrium position when displaced and released. Additional weights can be taped to the oscillating glider to increase its period.

  • G1-35: MASS ON SPRING - EFFICIENT MODEL

    G1-35
    Illustrate the motion of a mass on a spring.
    Just lift mass and release to start oscillations. This one is relatively efficient, so its vibrations last a long time.
    FS2

  • G1-54: MASS'S DOUBLE PENDULUM

    G1-54
    Demonstrate the transition of potential energy into energy of oscillation of the pendulum, and the operation of an escapement.
    Put your finger into a hole of a toothed wheel and rotate it counterclockwise 2 or 3 turns to give the spring energy or to lift the weight. For this purpose disconnect the wheel with anchor by pressing its axis. When this wheel is released, the pendulum starts to oscillate. This demonstrates one mechanism by which energy is fed into the pendula of large clocks.

    You can see a working simulation of the physics behind a clock escapement here: https://www.myphysicslab.com/engine2D/pendulum-clock-en.html

  • G1-82: PENDULUM WAVES

    G1-82
    Create waves in a very dramatic way using a series of fifteen carefully adjusted independent pendula.
    After the pendula are started into oscillation with the same phase, they pass through a series of various standing wave and traveling wave patterns, finally returning to their initial mode, in which they were all in phase. This is a GREAT demonstration - takes about one minute.

  • G3-01 SHIVE WAVE MACHINE - TRAVELING WAVES

    G3-01
    Demonstrates traveling waves

    Make sinusoidal waves by moving the spines at one end of the machine up and down sinusoidally, either with your hand or using the wave generator. Vary the amplitude and the frequency and observe the wavelength. You can show semi-quantitatively that the wave speed is approximately the same for all frequencies.
    Background
    The Shive wave machine illustrates transverse waves - the direction of displacement is perpendicular to the direction of transmission. This can be used as a model of many wave phenomena.
    FS0

  • G3-28 SUSPENDED SLINKY

    G3-28
    Shows longitudinal and transverse traveling waves & standing waves
    Transverse or longitudinal pulses can be created by appropriate motion of your hand at one end of the SLINKY. Using your hand you can also create transverse standing waves and discuss the overtone series. Gently vibrating one end of the spring (either by hand or using the motor) at the appropriate frequency creates longitudinal standing waves.
    FS1

  • G3-51 ROPE WAVE GENERATOR - FREQUENCY VS. WAVELENGTH

    G3-51
    Shows the relationship between frequency and wavelength for fixed tension cord
    Keeping the tension in the rope fixed (same weight on hook) and raising the frequency creates standing waves with shorter wavelength (more loops).
    FS1

  • G3-52: ROPE WAVE GENERATOR - ROPE TENSION VS WAVELENGTH

    G3-52
    Observe the change in wavelength of a vibrating rope as the tension is varied.
    Set the generator frequency using about 250g to produce 2 loops. Quadrupling the weight increases the wave speed (and thus the wavelength) by about a factor of two, creating one loop, while using about 110 grams creates three loops, two-thirds of the original wavelength. This is Mersenne's second law for stretched strings.
    FS1

  • G4-22: CHLADNI FIGURES - OSCILLATOR DRIVEN

    G4-22
    Show two-dimensional standing waves in a metal plate
    The Chladni plate is a system for creating and illustrating two-dimensional standing waves in a surface. A variety of flat plates can be mounted on the oscillator (including square, circular, and violin-shaped plates). As the plate vibrates, fine white sand is shaken about and traces out the nodal lines of the vibrations of the plate. The system operates by means of magnetostriction. A thin-walled annealed nickel tube is used to drive various Chladni plates. The nickel tube is threaded into the center of the plate, and inserted through a coil under the plate, which rests on a thick felt surface. An oscillator in the 10-30 kHz frequency range drives a 20-Watt audio amplifier to provide the current creating the magnetic field. The field is biased by a small horseshoe magnet to avoid frequency doubling in the tube. A mirror allows larger groups to view the plate easily.
    FS1

  • 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

  • H2-26: PHASE REVERSAL BETWEEN STEREO SPEAKERS - MUSIC

    H2-26
    Demonstrate interference of sound in a dramatic way.
    Two loudspeakers are connected in the monaural mode to the power amplifier and positioned close together as shown in the photograph at the left above. A switch box in the leads of one of the speakers allows reversal of the phase of that speaker. When music with lots of bass is played, flipping the phase reversal switch causes huge reduction in the amplitude of the bass frequencies. This is a very dramatic effect.

    A nice experiment shows the relation of phase to physical position. Play an 80 Hz tone into the two speakers, then reverse the phase to reduce the sound to virtually nothing. Uncoil the wire from the back of one speaker and move the speaker 12 or 15 feet across the front of the room; the loud bass tone returns! The waves from the two speakers are no longer out of phase. Can easily be combined with H2-27.
    FS1

    h2-26a

  • H2-55: BEATS AND RESONANCE - TUNING BOXES

    H2-55
    Illustrate beats and resonance.
    Adding a small clamp onto one of the tuning bars reduces its frequency. Striking two tuning bars, one with a weight, then produces beats. The frequency of the beats can be adjusted by varying the position of the weight on the bar.
    Without weights on either bar, strike one of the tuning bars, then hold the other adjacent to the struck bar for a few seconds. If the struck bar is then damped, the sound continues. The second bar is in resonance with the struck bar, and some energy is transferred if they are physically near each other.
    This demonstration is similar to demonstration H2-52, except for use of open tuning boxes for resonance. It is a bit louder for use in the lecture halls, but perhaps a bit harder to explain because of the resonant boxes.
    h2

  • H3-05: KUNDT'S TUBE - OSCILLATOR DRIVEN

    H3-05
    Demonstrate standing waves in an air column.
    An oscillator in the 1000-5000 Hz frequency range drives a loudspeaker at one end of a clear glass tube, with the other end stopped by a moveable plunger. Varying the frequency of the oscillator or the position of the plunger, one can obtain a series of standing wave patterns, which are made visual by the motion of cork dust in the bottom of the tube. The standing wave pattern is shown to large groups by placing the device on an overhead projector. This is a very dramatic demonstration, and is very effective in providing an introduction to standing sound waves. Examples of standing waves as seen using the overhead projector are shown below.

    Be aware that the tube is glass, and must be handled carefully.
    H2, ME3

    h3-05ah3-05b

  • H3-13: ROARING TUBE - 8 FT

    H3-13
    Demonstrate standing sound waves in air excited by convection currents.
    A switch is held closed, heating a nichrome wire coil in a vertical four-inch diameter galvanized steel downspout tube, leading to a very loud roar at about 65 Hz, the fundamental frequency of an eight-foot air tube. This is the classic Rijke tube demonstration with an electrical heater replacing a gas burner and screen as the source of the convection currents.

    Consider combing this with H3-12, and invite students to make predictions about the differences in pitch and volume.

    h3-13coilh3-13drawing

  • H3-23: RESONANCE TUBE - OSCILLATOR, PLUNGER AND MICROPHONE

    H3-23
    Demonstrate standing sound waves in a closed tube.
    An oscillator drives a small loudspeaker which is mounted at one end of a tube, with the other end stopped by a moveable plunger. A microphone adjacent to the loudspeaker at the open end of the tube is connected to the oscilloscope. When the frequency is varied or the position of the plunger in the tube is changed, sound resonances can be created in the tube and are displayed on the oscilloscope as an increase in amplitude. Resonances occur when the length of the tube is equal to any odd multiple of one-quarter wavelength of the sound wave.

    This is a variation on H3-22, and can be combined with it.

  • I3-31: IDEAL GAS LAW - VOLUME OF ONE MOLE

    I3-31
    Demonstrate that one mole of gas occupies 22.4 liters at STP.
    Pour liquid nitrogen into the small beaker and let it boil down to about 35 ml. The density of liquid nitrogen is 0.808 g/ml, so one mole has a mass of 28 grams and occupies about 35 ml. Install the neck of the balloon over the beaker, and allow the liquid nitrogen to evaporate, filling the balloon. Determine the average circumference of the balloon and from that calculate the diameter. The approximate volume of one mole of nitrogen gas at atmospheric pressure is then V= 4 pi r3/3, which can be readily calculated. This determination is good to better than ten percent.
    I3, I0

  • I3-42: BOYLED MARSHMALLOWS

    I3-42
    Amusing demonstration of Boyle's Law.

    A marshmallow is placed in a bell jar. As the air is pumped out of the jar the pressure inside becomes smaller and the little bubbles of air in the marshmallow increase in size, inflating the marshmallow. Eventually much of the air originally in the marshmallow is pumped away. When the air is let back in, atmospheric pressure compresses the marshmallow to a small fraction of its original size.

    An alternative demonstration uses a balloon with a small amount of air in it in place of the marshmallow. The photographs above show the marshmallow: before pumping, after pumping, and after the air is let back into the bell jar, and the balloon: before pumping and after pumping.

    Please bring own marshmallow.
    I3, FS1

    i3-42ai3-42bi3-42ci3-42di3-42e