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PHYS104

  • D1-41 ROTATING WATER BUCKET

    D1-41
    Demonstrates centripetal force and centrifugal reaction
    Put some water in the bucket and rotate the bucket in a vertical circle over your head. The centripetal force provided by your arm keeps the water bucket moving in a circle, while the centrifugal reaction keeps the water in the bottom of the bucket, as long as the rotational velocity is sufficient.
    D1

  • D1-44: ACCELEROMETERS AND FRAMES OF REFERENCE

    D1-44
    Demonstrate the direction of the acceleration in both rotational and translational coordinate systems
    In each experiment the ping-pong balls act as accelerometers. When the jars are rotated, the ball suspended from the bottom of the water-filled jar moves toward the direction of the acceleration, while the ball suspended from the top of the air-filled jar moves in the direction opposite the acceleration. The ping-pong ball in the water-filled tube indicates the direction of the acceleration when the tube is accelerated linearly or rotated.

  • D1-52: FAIRGROUND ROTOR

    D1-52
    Illustrate the application of rotational forces
    Place the little people onto their platform against the wall of the rotor and start the rotor in motion. A trip switch (just to the left of the peole in the close-up photo) removes the floor, but the people remain pinned against the wall due to centrifugal reaction, and do not fall due to friction with the wall of the rotor. When the rotor slows down, the frictional force of the people against the wall becomes less than component of the gravitational force down the wall and the people fall off the rotor. The entire assembly may be tilted while the rotor is in motion without causing the people to fall off.
    OS1

  • D1-53 LOOP-THE-LOOP

    D1-53
    Demonstrates centripetal force and conservation of energy in a rotating object

    This track can be described as three segments: the long upright segment, the loop, and the shorter upright segment. If you begin by placing the ball on the long upright segment at a height equal to the height of the loop (2R), the ball will roll down the track, begin to climb the loop, and then fall off and roll away. You can then repeat this at increasingly higher positions until the ball makes it all the way around the loop and begins to climb the shorter upright segment. In either case, be ready to catch it as it falls off afterwards!

    This is a good demonstration to encourage students to make predictions about its behaviour. Invite students to make arguments about what starting height will allow the ball to complete the full loop. A meter stick can be additionally provided upon request to aid in measuring the height.

    Background
    Motion of the ball down the track and around the loop-the-loop can be described in terms of gravitational potential energy, rotational and translational kinetic energy, and centripetal force. A ball of mass m and radius r must be released at some minimum height h above the bottom point of the track so that it will not leave the track while passing around the loop-the-loop.

    In order to stay on the track at the top of the loop the centrifugal reaction of the ball on the track must be equal to or greater than the gravitational force on the ball: mv^2/R = mg, or v^2 = gR, where v is its linear velocity at the top of the loop, R is the radius of the loop, and g is the acceleration of gravity. Conservation of energy dictates that at the top of the loop Iw^2/2 + mv^2/2 +2mgR = mgh, where the moment of inertia of the ball I = 2mr^2/5 and w is the angular velocity of the ball at the top of the loop.

    From these considerations we obtain the minimum starting height for the ball above the bottom of the loop-the-loop in order that the ball remain in contact with the track at all times: h = 2.7 R. In the case of an object sliding along a frictionless loop-the-loop, the height would be h = 2.5 R. Marks have been made at the points 2.5 R and 2.7 R. The ball remains in contact with the track at the top of the loop only when the height 2.7 R is reached, demonstrating the effect of the rotation of the rolling ball.
    FS2

  • D3-02: MASS ON STRING - ORBITS WITH VARYING RADIUS

    D3-02
    Illustrates conservation of angular momentum
    Rotate the mass on the string with the central end of the string passing through the tubular metal collar. Pulling the string decreases the radius of the ball, thus decreasing the moment of inertia and increasing the angular speed of the ball.
    D3

  • D3-03 ROTATING CHAIR AND WEIGHTS

    D3-03
    Illustrates conservation of angular momentum

    A subject, holding the weights with their arms extended, is started into rotation. When the weights are pulled inward to the chest of the subject, the moment of inertia of the system is decreased, leading to significant increase in the angular speed of the rotating chair.

    Please take care when using this device, especially when accelerating. You can gain a significant increase in rotational speed, so hold on! And it is best not to have a person push the chair around very much, as it is very easy to hit them with a weight by accident.

    Engagement Suggestions
    • Consider inviting a participant from the class.
    • Encourage students to predict what will happen before performing the demonstration.
    • Once the demonstration has been performed, discuss the activity both in terms of angular momentum and its conservation, and in terms of kinetic energy.
    • For extended discussion, introduce the idea of friction. How does friction work in this system? How does it affect the angular momentum? Where does the kinetic energy go?
    Background
    This device illustrates the conservation of angular momentum. When the heavy weights are moved closer to or farther from the axis of rotation, the distribution of mass and thus the rotational inertia (or moment of inertia) changes.

    To show this in a different way, a single user with a single weight can move themself in a circle by swinging their arm wide holding the weight from front to back, then drawing it inwards before extending their arm forwards again and repeating the motion. This is essentially a rotational analogue of pumping a swing.
    FS0

  • D3-05 ROTATING CHAIR AND BICYCLE WHEEL

    D3-05
    Illustrates conservation of angular momentum

    Sit on the chair (chair not rotating) with the wheel spinning and its axis oriented vertically. Reverse the angular momentum vector of the wheel by inverting the wheel, thus causing the entire chair to rotate in the original direction of the wheel rotation. Returning the wheel to its initial orientation causes the chair to cease its rotation.

    Because the friction in the bearing of the rotating chair is very low, several cycles of this procedure can usually be completed before the system loses its energy and stops.

    Engagement Suggestions
    • Consider inviting a participant from the class.
    • Note that this demonstration can lead to sudden changes in motion. Be careful not to collide with your volunteer.
    FS0

    Bicycle Wheel Gyro v2

  • D4-03: BICYCLE WHEEL GYROSCOPE ON PIVOT

    D4-03
    Demonstrates gyroscopic precession and nutation
    Spin the bicycle wheel and release it with a small push to obtain pure precession, or release it without simultaneously pushing it to obtain precession with nutation. Release it with no spin to show that precession only occurs with the pre-condition of angular momentum of the wheel.

  • D4-22: MONORAIL CAR

    D4-22
    Demonstrate gyroscopic stability
    The gyroscope on the car is driven to a high rotational speed using a motor. The car will then remain balanced on the wire for over thirty seconds.
    D4, OS0

  • F1-01 FLUID PRESSURE VS. DEPTH

    F1-01
    Demonstrates that fluid pressure increases linearly with depth and is isotropic.
    An L-shaped glass tube connected to a liquid manometer is inserted into a tank of water. The pressure in the water tank can be measured at any depth. Holding the tube at a particular depth and rotating it about the end will show no change in pressure, demonstrating that pressure is isotropic.
    F1, FS2

  • F2-05 BUOYANCY - BOAT AND ROCK

    F2-05
    Illustrates buoyancy
    Boat and rock float in a closed pond. removing rock from boat and dropping it in pond will cause the water level of the pond to go down
    F2

  • 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

  • G1-33 MASSES AND SPRINGS WITH SPIDER

    G1-33
    Compares frequencies of various mass-spring combinations
    Hang various masses on various springs and observe the oscillations. Notice that the damping is greater for the mass on the rubber band.
    FS1

  • 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.

  • 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

  • G3-28 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