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PiP Dec 2015

  • C3-04: INERTIA - LEAD BRICK AND HAND

    C3-04
    Illustrates inertia of rest

    Place the lead brick gently on your fingers and strike the lead brick sharply with the hammer. The inertia of the lead brick prevents damage to your fingers.

    Engagement Suggestion
    • This is a visually impressive way to get students’ attention at the beginning of a discussion of inertia.
    • This can be used as a volunteer participation demonstration, but please be very careful.
    C3

  • C3-12 PENCIL AND PLYWOOD

    C3-12
    Dramatically demonstrate inertia

    A pencil is accelerated to almost the speed of sound by blasting it through a four-foot tube using a carbon dioxide fire extinguisher. The pencil will readily impale itself through a piece of 3/8" plywood. With a little bit of luck the pencil point will be virtually intact, although sometimes you need to re-sharpen it after the demonstration.

    CAUTION: Be sure that the hose fitting is securely attached to the tube and that the plastic shield is in place before firing. The shield should be latched in place, with no debris blocking its edge from meeting the baseplate

    Engagement Suggestions
    • • Before using, encourage your students to predict what will happen to the pencil.
    • • For advanced students, discuss the energy involved in the problem and where the kinetic energy of the pencil went after the collision.
        • Background

        This demonstration can be presented in multiple ways. It has been offered classically as an illustration of the principle of inertia – the pencil is in motion at a high velocity, and continues in motion despite the intervening wood until arrested by a greater force. Alternatively, consider the high velocity and high momentum of the pencil. The abrupt deceleration at the plywood means a high impulse. The pointed pencil has a very small cross-sectional area, resulting in force applied over a small area leading to a high momentary pressure.

        Linked below is a slow-motion video of the collision, shot at 600 frames per second. A fun class activity could be to use the video to measure the motion of the pencil and estimate its momentum and kinetic energy, based on what you see in the video and by measuring typical lengths and masses for wooden pencils.

    FS1

  • C5-14 ROCKET TRIKE

    C5-14
    Demonstrate Newton's third law of motion

    Pressing the fire extinguisher handle expels carbon dioxide out a nozzle straight behind the tricycle, causing forward thrust of the tricycle. Be sure the exhaust is not oriented to hit the audience or anything else likely to be adversely affected but a sudden blast of cold air.
    Background
    This is a dramatic illustration of Newton's Third Law of Motion: the principle of action and reaction. The mass of gas being ejected out of the back of the tricycle at a very high velocity imparts an equal and opposite force to the tricycle, which thus moves forward. The tricycle is much more massive, so it does not move as quickly, but the acceleration is still very real - be careful not to run into the wall!
    FS1

  • C7-19: GAUSSIAN GUN

    C7-19
    Demonstrate transfer of energy in an elastic collision
    Ball bearings in a track are accelerated by a magnetic field, showing a collision where momentum appears to not be conserved.

    Compare to K2-40: Magnetic Accelerator
    OS0

  • F4-42: SMOKE RINGS USING GARBAGE CAN

    F4-42
    Create large smoke rings and illustrate the circular vortex.
    Fill the garbage can with smoke from the electronic fog machine; it takes a few minutes for the machine to warm up before it can produce good fog. To create giant smoke rings, aim the can and tap the rubber membrane covering the lid opening.

    f4-42af4-42bf4-42cf4-42d

  • G1-74: LISSAJOUS FIGURES - LASER AND LOUDSPEAKER

    G1-74
    Show Lissajous figures created by music to form a laser show.
    A front-surface mirror is suspended in front of the center of a large loudspeaker in an orthogonal suspension. A laser beam bounces off the mirror onto a nearby white screen, creating varying Lissajous patterns as the music plays. This suspension encourages the mirror to move with two basically orthogonal oscillations, combining to form Lissajous figures, as seen above.
    OS5

  • 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

  • H1-01 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

  • H1-31: SOUND LEVEL METER

    H1-31
    Demonstrate use of a sound level meter.
    Several loud sources can provided upon request, including musical instruments, noisy laboratory apparatus, and a portable audiotape machine with earphones. You can also invite students to bring up their own devices to test. It is surprisingly easy to get over 100dB in earphones. The sound level meter can viewed by a TV camera and displayed on the main screen.

  • H2-33: SPEAKER AND EXPONENTIAL HORN

    H2-33
    Demonstrate the effect of an exponential horn enclosure.
    A small loudspeaker is held up behind the opening of an exponential horn. The sound becomes much louder, especially in the bass. A horn enclosure has the effect of taking an extended source such as a loudspeaker and creating the best impedance match with the outside world, providing the most coherent plane wave. Compare this to H2-32, which uses the same speaker with a flat baffle. Invite students to speculate about what the effects the different shapes have.
    H2, OS5

  • H3-12: ROARING TUBE - 4 FT

    H3-12
    Demonstrate standing sound waves in air excited by convection currents.
    A switch is held closed, activating a nichrome wire coil in a vertical glass tube, leading to a very loud roar at about 130 Hz, the fundamental frequency of a four-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 H3-13, and invite students to make predictions about the differences in pitch and volume.
    FS1

  • H3-17 FLAME TUBE

    H3-17
    Demonstrates standing waves in a tube
    A loudspeaker in one end of a four-inch diameter galvanized iron tube creates standing waves in propane gas in the tube. The gas emerges out of a series of small holes in the top of the tube, forming a long line of flames when lit. Any sound resonant with the length of the tube can create standing waves in the gas which are readily visible as a pattern in the height of the flames. Both rhythm and frequency response can be seen nicely in music. An oscillator and a cassette deck are provided with the demonstration to be used as simple sources for the loudspeaker. Or, a voice or other music or audio can introduced using a microphone and amplifier or external input jacks, available upon request.
    FS1

  • H3-71 STROKED ALUMINUM ROD

    H3-71
    Illustrates longitudinal standing waves in an aluminum rod.
    Apply powdered violin rosin to your fingers or wear a rosined glove and stroke the aluminum rod firmly while holding it at a nodal point. Holding it in the center produces the fundamental, holding at 1/4 of the way from one end produces the second harmonic, holding at 1/6 of the way from one end produces the third harmonic, etc. The rod is about 6 ft long, and the speed of sound in aluminum is about 16,700 ft/sec, so the frequency of the fundamental is about 1400 Hz. The sound is very loud and lasts a long time; the Q for this system is around 100,000!
    Alternatively, request an (optional) mallet to use with the rod. Use the mallet to strike the rod on one end; by holding the rod at a node or antinode, all or some modes can be excited or damped.

  • H4-22: BOTTLE BAND

    H4-22
    Demonstrate how edge tones and Helmholtz resonators can be used to create a bottle band.
    This demonstration requires a bass bottle player, three alto bottle players, and a recorder player, but can be rehearsed for a polished performance in a few minutes. The bass bottle player has three notes, while each of the alto bottle players is limited to two notes, so major musical experience is not necessary. The recorder player plays the melody of the song ("Home, Home on the Range" or "Ach du lieber Augustine") while the bottle band vamps.

    Consider inviting students to volunteer in the class period before, then come early to class to try it out. Note that the recorder is also available separately as H4-42.

    H4

  • H5-01: EAR MODEL

    H5-01
    Illustrate the parts of the ear, their spatial relationships, and their functions.
    This model nicely shows how the major organs of the ear are physically arranged. The bone chain, the cochlea, and the semicircular canal assembly are removable. The fact that space is three-dimensional leads to the necessity of three orthogonal semicircular canals, which can easily be seen. The interesting parts in the middle and inner ears are shown in the close-up photograph.
    H5

  • I1-15: THERMAL EXPANSION - PIN BREAKER

    I1-15
    Demonstrate thermal expansion in a dramatic way.
    A pin is inserted into a hole in a long steel rod, one end of which is fixed on the apparatus. The pin sticks out of the hole and rests against a fixed plate at the right side of the device, under the shield. When the rod is heated over period of several minutes, it expands such that the pin pushes against the plate, as seen in the photograph at the right, until the pin snaps. This is a fairly dramatic demonstration which illustrates the magnitude of the forces which can build up during thermal expansion.
    I1, I0

    i1-15a

  • I3-16: COLLAPSE OF CAN - LARGE PUMP

    I3-16
    Demonstrate the forces created by atmospheric air pressure.
    Start the mechanical vacuum pump, then place a soda can firmly on the top gasket around the pump opening. In a couple of seconds enough air is pumped out of the can so that the can collapses with a bang, jumping off the pump.
    FS1, SU14

    i3-16ai3-16b

  • I3-18: VACUUM BAZOOKA

    I3-18
    Illustrate one effect of atmospheric pressure and force.
    A tennis ball is positioned near one end of an evacuated tube. When the plate sealing that end of the tube is rapidly knocked off, air at atmospheric pressure enters the tube. The ball is propelled by the force arising from the atmospheric pressure of air to create a bazooka effect along with a loud noise.
    I3, I0

    i3-18a

  • I4-36: REGELATION - ICE UNDER PRESSURE

    I4-36
    Demonstrate regelation.
    A thin wire with weights on the ends is looped over an ice cube. In a few minutes the wire will cut through the ice cube and the weights fall with a bang onto the stand. The ice re-freezes after the wire passes, leaving a single cube of ice. The photograph above shows the wire cutting through the ice cube.

    i4-36a

  • J4-32 DISCHARGE OF CAPACITOR WITH BANG

    J4-32
    Demonstrates that capacitors store electrical energy
    A 3500 microfarad capacitor is charged to 100 volts using the battery pack. Touch the capacitor terminals to the copper contacts on the battery pack; check that the polarity is correct, this is an electrolytic capacitor. Discharging the capacitor with the large screwdriver produces a very loud BANG.
    J4