Follow

Safety Equipment: Goggles

  • B3-21: CHISEL AS WEDGE

    B3-21
    Demonstrate the mechanical advantage of a wedge

    A wedge is used to split a piece of wood.

    For your safety, goggles are provided
    B3

  • B4-11: ELASTIC LIMIT OF RUBBER BAND

    B4-11
    Demonstrate Hooke's law and elastic limit.
    Load small weights to demonstrate Hooke's law. Hanging a few kilograms from the rubber band exceeds its elastic limit.
    FS2, ME1

    b4-11a

  • B4-14: ELASTIC LIMIT OF WIRE

    B4-14
    Demonstrate the variation in tensile strength with wire diameter.
    Two wires are used: 24 AWG, 0.474 mm diameter, and 20 AWG, 0.786 mm diameter. The ratio of tension required to break two wires is proportional to the square of their diameters, for this case F2 / F1 = 2.75. The two wires can be broken, the required tensions read off the attached spring scale, and the ratio calculated.
    B4

  • B4-31: FAILURE OF WOOD IN COMPRESSION

    B4-31
    Demonstrate the dependence of the compressional strength of wooden dowels on their diameter and length.
    Place dowel vertically between the plates of the hydraulic press, and compress dowel until it collapses. A 5/8" dowel requires about 1.0 tons, a 7/8" dowel about 2.2 tons.
    B4, FS1

    b4-31a

  • C5-16: HERO'S ENGINE

    C5-16
    Demonstrate action and reaction in a rotational system.

    The boiler is partially filled with water and heated until steam is produced. The steam emerges from right-angle arms on the side of the boiler, causing the boiler to rotate in the direction opposite to that of the emerging steam.

    Danger:Do not tilt burner until it is warm.
    C5, I0

  • C5-17: ROCKET BOTTLE

    C5-17
    Illustrate the rocket principle in a dramatic way
    Pour about 100-200 ml of liquid nitrogen into the bottle and install the stopper. Exhausting nitrogen gas and liquid result in motion of the bottle. An untethered stopper is available for comparison.
    OS6, I0, F2

  • C7-51: BALLISTIC PENDULUM - PELLET GUN

    C7-51
    Determine the speed of an air gun pellet using a ballistic pendulum.
    The pellet from an air gun is shot into a foam-filled can, which acts as the pendulum. Conservation of linear momentum in the inelastic collision determines the speed with which the pendulum receptacle leaves the collision. Conservation of energy determines how high the pendulum will rise, or alternatively, the maximum angle to which it swings. Working backward, we can determine the velocity v of the pellet: v = [(M + m)/m] SQRT (2gh), where m is the mass of the pellet, M is the mass of the receptacle can, h is the height to which the can rises, and g is the acceleration of gravity. The height h is determined by measuring the radius R of the pendulum and the horizontal displacement x of the receptacle can after the collision. Be familiar with the safety mechanism, and know where the pellet exits the gun before firing. Pump gun ONCE before firing.

  • C7-53: AIR TRACK - SPEED OF AIR GUN PELLET

    C7-53
    Determine the speed of an air gun pellet using conservation of momentum in an inelastic collision.
    The pellet is shot into a receptacle mounted on an air track glider. Conservation of momentum in the ensuing totally inelastic collision allows determination of the velocity v with which the pellet was shot: v = [(M+m)/m] V, where m is the mass of the pellet, M is the mass of the glider/receptacle, and V is the measured velocity with which the glider leaves the collision. The speed of the glider is determined using a photocell gate timer. Compare this result with the result from the standard ballistic pendulum demonstration using the air gun pellet, Demonstration C7-51. Pump the gun once only. Be familiar with the safety mechanism, and know where the pellet exits the gun before firing.

  • D1-02: PELLET VELOCITY FROM ROTATING DISCS

    D1-02
    Determine the speed of a B-B using rotational kinematics.
    A B-B is shot from the air gun with a linear velocity v, such that it passes between the two rotating discs which have a separation d and are rotating with an angular velocity w. The angle a that the two discs rotate while the B-B is traveling between them is determined by inspecting the two discs. The velocity of the B-B is then determined by using the relation: v = w d / a. In this case the angular velocity w of the rotating discs is 1800 rpm, and the distance d between the discs is 1 meter. CAUTION: Lift apparatus by handles only. Pump just before firing to assure uniform velocity for several trials. See also Demonstrations C7-51: BALLISTIC PENDULUM - PELLET GUN and C7-53: AIR TRACK - SPEED OF AIR GUN PELLET for other ways to determine the B-B velocity.

  • 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

  • I1-11 THERMAL EXPANSION - BALL AND HOLE

    I1-11
    Illustrates thermal expansion
    At room temperature the ball will not fit through the hole in the metal plate. When the plate is heated by a burner for about 30 seconds, the ball easily fits through the hole
    I1, I0

  • I1-12: THERMAL EXPANSION - BALL AND RING

    I1-12
    Demonstrate thermal expansion.
    When both ball and ring are at room temperature, the ball fits through the ring. If only the ball is heated, it expands so that it will not fit through the ring.
    I1, I0

  • I1-13 THERMAL EXPANSION - BIMETAL STRIP

    I1-13
    Demonstrates differential thermal expansion

    Two strips of different metals, invar steel and brass, are welded together to form a bimetal strip. Since each metal has a different coefficient of thermal expansion, heating the bimetal strip will result in the metals expanding at different rates, causing it to bend.

    When heating, always wear goggles and handle the flame with care, ensuring that it is not pointed near students or flammable materials. Use in a well ventilated classroom.

    Engagement Suggestion
    Ask your students: • Which metal will expand more when it is heated, and why?
    • What happens when it is cooled?
    • How could you make use of this to measure or control something?
    Background

    The amount a metal expands or contracts with temperature is governed by its coefficient of thermal expansion, a property which varies between different metals depending on their molecular structure. Invar steel is an alloy designed to have an exceptionally low coefficient, about one-tenth that of most steel, while brass has a higher coefficient than even ordinary steel. So the brass expands much more rapidly than the steel does when heated.

    Bimetallic strips like this are used in some types of thermometers and thermostatic controllers (including many older window thermometers and household thermostats). Check out demonstrations I1-17 and I1-18 for examples and to see how this works.
    I1, I0

  • 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

  • I1-16: THERMAL CONTRACTION OF CUPS WITH LN

    I1-16
    Measure coefficients of linear expansion.
    A cup rests on a fixed platform with the rim of the cup under the feeler gauge. Pour liquid nitrogen into the cup to make it contract and read the length contraction (ha! ha!) on the gauge.

  • I1-17: THERMOSTAT - MODEL

    I1-17
    Model of use of a bimetal strip in a thermostat.
    A bimetallic strip is set up to complete a circuit and turn on a bulb, as a model of how thermostats move with changing temperature to control furnaces or air conditioners. Heat the bimetal strip so that it curves toward the wire. When it touches the wire it completes the circuit, lighting the bulb. This is similar to the mechanism in a real bi-metal strip thermostat to turn on and off the power to the appliance.
    I1, I0, K6

    i1-17a

  • I1-51: RUBBER AT LN TEMPERATURE

    I1-51
    Demonstrate how a normally elastic material at room temperature becomes rigid at very low temperatures.
    Dip a rubber sample into the liquid nitrogen with the tongs, then place it on a wooden "anvil" and hit it with a hammer to break it. Show the students in the audience how the material's property change with temperature.
    I0, I1

  • I1-52: TUNING FORK AT LIQUID NITROGEN TEMPERATURE

    I1-52
    Demonstrate the change in frequency of a tuning fork at liquid nitrogen temperature.
    Cool down one of the two identical tuning forks in liquid nitrogen. When it is cooled, beats are observed between identical tuning forks, one of which has been cooled.

  • I1-53: LEAD BELL AT LIQUID NITROGEN TEMPERATURE

    I1-53
    Demonstrate the effect of temperature on vibrations in a lead bell.
    The bell can be sounded at room temperature. It is then cooled by placing it in a bath of liquid nitrogen, after which it is sounded at LN temperature. The difference in the tone can be ascribed to the increased crystalline structure when the bell is cooled.

  • I1-61: DUST EXPLOSION

    I1-61
    Produce a dust explosion.
    A rounded tablespoon of lycopodium powder placed in the funnel is blown upward by blowing into the end of the rubber tube, which can be stretched out. When the cloud of powder reaches a burning candle flame, on the top mount, it ignites readily to create a dust explosion. This is a very dramatic effect.
    I1, I0, C2, FS2

    i1-61ai1-61b