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PHYS410

  • D2-21: CENTER OF PERCUSSION - BAT AND MALLET

    D2-21
    Demonstrate the center of percussion using a baseball bat.

    The bat is held at the small end and struck soundly with the mallet at the bigger end. A yellow marker marks the location of the center of percussion. When the bat is struck below the center of percussion it will spin out of the holder's fingers moving in the opposite direction to that of the incoming mallet. When the bat is struck above the center of percussion it will spin out of the holder's fingers moving the same direction as the incoming mallet. When the bat is struck at the center of percussion it will rotate about the holder's fingers, but will not spin out of the fingers.

    This illustrates how a ball player wants to hit the baseball to get the greatest momentum transfer to the ball with the least reaction force on the batter's hands and arms. A tennnis stroke works the same way. You can minimize "tennis elbow" by hitting the ball at the center of percussion of the racket so that the rotational reaction on your wrist and elbow is minimized.

    Click your mouse here to see the collision of a baseball and a softball with composite bats, taken by a slow motion camera.

    Click your mouse here to see the vibrational modes of a baseball bat.

  • D4-01: GYROSCOPE WITH COUNTERWEIGHTS

    D4-01
    Illustrate precession and nutation with a precision gyroscope.
    Start the massive flywheel rotating and observe no precession when the flywheel is statically balanced with the counterweights. Unbalancing the counterweights creates precession of the gyroscope. Lifting the unbalanced gyroscope slightly before releasing it results in nutation.
    D4

  • D5-23: ROTATING BEAD ON LOOP

    D5-23
    Demonstrate the presence of a "critical parameter" which determines the dynamic behavior of a simple physical system.
    Attach the mounting frame to the variable speed rotator and adjust the rotation rate to less than approximately 1.6 revolutions per second. The bead remains in equilibrium at the bottom of the loop. For rotational rates greater than 1.6 revolutions per second, the bead will be in stable equilibrium at a non-zero angle dependent on the rotation rate. Frictional effects are considerable; nevertheless the presence of a critical angular velocity can be seen.
    D5, D1

  • F4-32: SIPHON - CHAIN MODEL

    F4-32
    illustrate how a siphon works.
    A bead chain passes over a pulley between two beakers. When one of the beakers is raised, the chain flows from the higher into the lower beaker, just as water flows from the higher to the lower container of a siphon. This is due the greater weight of the chain, or water, on the side of the lower container. Note that the cause of the siphon flow is not air pressure, which is greater at the surface of the lower container!

  • 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

  • G1-15 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

  • G1-60 CHAOS - TWO BIFILAR PENDULA

    G1-60
    Illustrates chaotic motion
    The two pendula are started into apparently identical oscillations, but their motion soon diverges. No matter how closely the motions of the two pendula are started, they eventually must undergo virtually total divergence.

    Eric Neumann has created an online simulation that can be used to model one of the legs of the pendulum. Try experimenting with the simulation as well, and see how sensitive it can be to its initial conditions. https://www.myphysicslab.com/pendulum/double-pendulum-en.html

    G1

  • G2-27: COUPLED SERIES MASSES HANGING ON SPRINGS

    G2-27
    Illustrate coupled oscillations and normal modes.
    Pushing either mass causes oscillations which will couple between the two masses. If the two masses are displaced from equilibrium by the appropriate amount either (1) in phase, or (2) out of phase, the normal modes can be produced. Alternatively, moving your hand up and down at the frequency of a normal mode will excite that mode.

    Check out Erik Neumann's Double Spring simulation here!
    G2

    g2 27edit

  • 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

  • G3-23: TRANSVERSE WAVES ON A LONG SPRING - FREE END

    G3-23
    Show reflections at a free end.
    A string holds one end of the long tight spring to the clamp on the lecture table. Because the string is long, and light compared to the spring, this forms a free end for the spring, allowing the end of the spring moves when a wave approaches.
    G3

  • 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

  • H3-72: TUNING RODS

    H3-72
    Hear longitudinal standing wave resonances in aluminum rods.
    Hold the tuning rod by the center fixture and strike it longitudinally on its end with a rubber mallet to excite the standing wave. The three rods pictured are calibrated: 5000 Hz, 10,000 Hz, and 15,000 Hz.

  • K2-64: UNIPOLAR GENERATOR

    K2-64
    Demonstrate unipolar generation of DC voltage, which may involve an explanation other than electromagnetic induction.
    A strong (over 10 kilogauss) cylindrical magnet is rotated about its axis at 1725 RPM. Brushes positioned on the axis of rotation and the "equator" of the bar magnet (midway between the two poles) are attached to a digital voltmeter. An electrical potential of about 15 millivolts is measured. Reversing the direction of rotation or reversing the ends of the magnet causes the DC voltage to reverse in sign. An aluminum bar can be substituted for the magnetic one and rotated in the CW or CCW directions. Note that there is a small (about 0.1-0.3 mV) potential developed with this arrangement, probably due to contact potentials between the various materials in the system and the wires, similar to the potential developed in a thermocouple. The observed potential is the same for either rotational direction of the aluminum rod; it would likely be opposite in sign for opposite rotation direction if it were due to some sort of induction effect. The explanation of this device is perhaps problematic. Many people believe that because there is no change in flux in the wire loop this cannot be an electromagnetic induction effect; the only explanation lies in special relativity. Other theoreticians disagree.
    K2, ME2