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PHYS273

  • G1-01 EXAMPLES OF SIMPLE HARMONIC MOTION

    G1-01
    Illustrates simple harmonic motion

    This demonstration lets you compare three typical pendula: a simple pendulum (mass on string), a physical pendulum (swinging rod), and a mass on a spring. Any of these produce simple harmonic motion, with a variety of periods. Useful for showing that the same equation describes the motion of any type of oscillating body.
    You can also compare these real-world pendula with some simulated ones:
    1. Erik Neumann's Single Spring simulation
    2. Erik Neumann's Pendulum simulation
    3. PhET Masses on Springs
    4. PhET Pendulum Lab
    FS2

  • 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

  • G1-15 PENDULA WITH 4 TO 1 LENGTH RATIO

    G1-15
    Shows that period of a simple pendulum is proportional to the square root of its length
    The two pendula are started in phase. The shorter pendulum undergoes two complete oscillations for each oscillation of the longer pendulum.
    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.

  • G2-07: PSYCHOACOUSTIC VIBRATION TRANSDUCER

    G2-07
    Challenge your students to recognize pseudoscience while illustrating resonance
    A traditional explanation: "When a group of people concentrate on one of the pendula, held as shown by the instructor, their psychoacoustic brain waves rapidly become in phase, producing enough mechanical energy to make only that pendulum oscillate."

    Of course, this is actually a demonstration of driven resonance - with a bit of practice, via small movements of your hands you can drive any one of the pendula you choose. Encourage your students to analyze pseudoscientific explanations for real phenomena.
    G2

  • G2-21 COUPLED PENDULA

    G2-21
    Demonstrates coupling of motion between two pendula of the same length
    The pendula are hung from a rod which can rock back and forth to transfer the motion from one pendulum to another. If you start the pendulum at the left in motion (in and out of the picture), the motion will couple back and forth between the pendula of the same length, leaving the others with only a slight perturbation. It is of interest to note the phase of the two pendula as the motion is transferred back and forth.

    Invite a student up to measure the pendula to confirm that the responsive one matches in length.

  • G2-22: BAR-COUPLED PENDULA

    G2-22
    Demonstrate a coupling resonance and to show normal modes.
    By starting either pendulum in motion in the plane of the picture, one observes transfer of the motion between the two pendula. One can also produce the two normal modes: both pendula moving in phase, or the pendula moving out of phase.
    FS2

  • G2-23: SPRING-COUPLED PHYSICAL PENDULA

    G2-23
    Demonstrate resonance and normal modes.
    After starting one of the pendula into motion in the plane of the picture, the motion couples back and forth between the two physical pendula at a rate determined by the spring constant and its location. Coupling can be varied by sliding the spring clamps along the pendula shafts. Normal modes can be nicely demonstrated.
    FS2

  • G2-24: COUPLED PENDULA - 100 TO 1 MASS RATIO

    G2-24
    Illustrate mechanical resonance.
    The two pendula have the same length, but the mass of the upper bob is 100 times that of the lower bob. With the masses hanging motionless, gently tap the bigger mass. Its energy will couple to the smaller mass, causing the smaller mass to oscillate with a much larger amplitude. The energy then couples back to the larger mass, and the cycle repeats.

  • 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

  • G3-05: SHIVE WAVE MACHINE - PARTIAL REFLECTIONS

    G3-05
    Show that a wave will be partially reflected at a point where the impedance changes.

    The Shive Wave Machine illustrates transverse waves traveling down a torsional wire. Partial reflection can be produced by
    • • linking the two different segments as shown in the photograph,
    • • adding weights to the end of a central crossarm to produce an impedance glitch, or
    • • attaching the dashpot at a central location and adjusting it for partial absorption of the incoming wave.
    Background
    Changing the arm mass changes the impedance of the medium. This changes the transmission speed; and when a wave passes through the junction, it may be partially reflected. Like a reflection from a free or fixed end (G3-03), this partial reflection can also be upright or inverted. Passing from higher to lower impedance gives an upright partial reflection; passing from lower to higher impedance gives an inverted partial reflection.

  • G3-21 TRANSVERSE WAVES ON A LONG SPRING

    G3-21
    Demonstrates traveling waves

    Clamp the spring to the lecture table and then step back. When you hold the other end with some tension and shake the end with various frequencies, you can illustrate transverse waves traveling along the spring.

    You can move your hand to generate a pulse or wave in the spring. Because of the clamp, the spring acts as a medium with one free end and one fixed end. By changing how far and how fast you move your hand, I can generate different amplitudes and frequencies. If you move my hand farther on each swing, you create a wave with a greater amplitude – the height of each peak is greater. If you move your hand up and down faster, you create a wave with a greater frequency – the number of peaks within a given length is greater.

    With practice, you can also find the natural frequency of the spring and set up standing waves.
    Engagement Suggestion
    • Ask students: “Now that we’ve seen some features of transverse waves, let’s try an experiment. I’m going to send a single upright pulse down the spring. What will happen when it reaches the fixed end? Will it stop entirely, bounce back in the same shape, or bounce back upside-down?”
    • “The pulse returns upside-down!”
    Background
    A transverse wave is one where the direction of oscillation is perpendicular to the direction of propagation. The up-and-down motion of the spring that forms each pulse is at a right angle to the forward movement of the wave. When a transverse pulse reflects off a fixed end, it returns inverted. If instead it had reflected off an open end, it would return upright. We can see this most easily with a single pulse, but this is true of a repeating waveform as well. We see mechanical transverse waves in springs, ropes, and other objects routinely. But another type of transverse wave surrounds us all the time – electromagnetic waves, like light, are transverse waves.
    G3

  • G3-25: SLINKY ON LECTURE TABLE - IMPEDANCE MISMATCH

    G3-25
    Show partial reflections and dependence of wave speed on density of the medium.
    A string (running inside the SLINKY) connects one end of a SLINKY with a point about 3/4 of the way from that end, with the end taped to one end of the lecture table. When the SLINKY is extended it has regions with two different densities, causing two different wave speeds. A wave started at the free end of the SLINKY (right side in photographs above) will experience an impedance change; it may produce (quickly attenuated) partial reflections at the boundary. The wave moves more slowly in the section at the left, as seen in the photograph at the right.
    G3

    g3-25a

  • G3-43 WHIP

    G3-43
    Illustrates transverse wave motion.
    A wave started down the whip increases its velocity as the whip decreases in diameter toward the tip. By the time the wave reaches the tip of the whip, the velocity of the whip motion can become greater than the speed of sound in air. The "cracking" of a whip is believed by many physicists to be a result of the sonic boom thus created.

    Please consider carefully how to appropriately present this device in class if used.
    G3

  • H1-41: ULTRASONIC MOTION DETECTOR

    H1-41
    Demonstrate how an ultrasonic motion detector works.
    This device senses motion by comparing the Doppler shifted wave reflected by a moving object with the original wave created by the device. Any frequency change is accompanied by a continuous phase change between the two waves, which is sensed and ultimately turns on a light bulb on top of the unit, corresponding to the alarm.

    (1) Moving some object toward or away from the device sets off the alarm light.

    (2) Moving an object across the beam does not cause a Doppler shift, and therefore does not set off the alarm.

    (3) The frequency of the emitted wave is about 40 kHz. With a wave generator and supertweeter, one can shine waves of about 40 kHz on the receiver transducer, fooling the device into thinking that a moving object is in the vicinity (as seen in the photograph).
    H1, ME3

  • H1-44: ULTRASONIC MOTION DETECTOR WAVE FORM

    H1-44
    Show the wave form of the ultrasonic signal created by the ultrasonic motion detector.
    A microphone is used to pick up the signal from the ultrasonic motion detector; that signal is then amplified and viewed using an oscilloscope. The wave form consists of bursts of 45 kHz ultrasound at intervals of about 25 milliseconds. Above is the signal seen by the oscilloscope with the horizontal scale at 10 ms/division (left) and at 100 microseconds per division (right).

    A question for students: Why do motion detectors use such high frequencies?

  • 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

  • K7-24: RLC CIRCUIT - 60 HZ WITH LIGHT BULB LOAD

    K7-24
    Demonstrate a series RLC circuit in a graphic way.
    A series RLC circuit, shown in the diagram above, consists of a variable inductor, a fixed capacitor, and a light bulb serving as the resistor. The capacitor and the inductor can be removed from the circuit using parallel switches. When the capacitor is in the circuit, the inductance can be adjusted so that the bulb is brighter, dimmer, or the same intensity as when the capacitor is out of the circuit. The photograph above shows the inductance in its resonance position. The photographs above show what happens when the inductor is shorted out (left), the capacitor is shorted out (center), and both are shorted out (right), so that the bulb is simply wired across the 110VAC power source.

  • K8-01 ELECTROMAGNETIC WAVE - MODEL

    K8-01
    Shows the relationship between the electric and magnetic field vectors in a plane-polarized traveling electromagnetic wave
    Red pegs represent the electric field vector and blue pegs represent the magnetic vector. The spatial relationship between these vectors and the direction of propagation can be seen. By moving the model along its axis the temporal aspect of the wave can be shown. This wave has a wavelength of 0.81 meters, and as an EM wave would have a frequency of 370MHz
    FS1

  • K8-42: RADIOWAVES - ENERGY AND DIPOLE PATTERN

    K8-42
    Demonstrates transmission of energy in electromagnetic waves. Shows the radiation pattern of the dipole antenna

    This demonstration is centered on a simple radio transmitter with an antenna, which sends a signal to a handheld dipole antenna connected to a light bulb. The receiving antenna can be moved around in space, keeping the two antennas parallel, to observe the dipole radiation pattern. Rotating the receiving antenna to a vertical orientation shows that the radiowaves are polarized, as seen by the light going out.
    Background

    An antenna receives an induced current from the electromagnetic field of the passing wave. The dipole is a linearly polarized antenna, sensitive to signals oriented in a particular direction. In this experiment, we can see this dramatically, as changing the orientation of the antenna relative to the source produces a significant drop in signal strength, so that it is no longer receiving sufficient energy to light the bulb.

    Compare this effect to other wave and polarization demonstrations in sections G3 and M7.
    FS1