Follow

PHYS115

  • B1-02: CENTER OF MASS - LEANING TOWER

    B1-02
    Demonstrate the effect of center of mass location
    A model tower is comprised of two sections; an askew bottom component and a top component. The bottom component is in a stable equilibrium when sitting on a horizontal surface since the horizontal position of its center of mass is within the perimeter of the base. As the top section is placed onto the base tower, the horizontal position of the center of mass will shift outside the base perimeter, thereby causing the system to be unstable and topple.

    Questions: Would anything change if the tower was hollow? Would the center of mass change? What should you do in order to keep the tower (consisting of both components) stable?

    B1

  • D1-55: ROTATING ELASTIC RINGS

    D1-55
    Demonstrate "centrifugal reaction" and to indicate why the earth is oblate.

    We have a pair of thin steel rings mounted on a rotating base. The top of the rings is free to slide along its axis, while the bottom is fixed to the rotating base.

    Turning the crank causes the elastic rings to rotate about the vertical axis. The rotation mechanism here uses the mechanical advantage of a large cranked wheel driving a smaller pulley to give the rotating rings a very high angular velocity.

    Engagement Suggestion
    Before rotating at high speed, invite students to predict what will happen to the rings when you get it spinning as fast as you can. Will they:
    • a) keep their circular shape
    • b) flatten at the top and bottom and bulge in the middle
    • or c) extend upwards and grow narrower in the middle?
    Afterwards, encourage students to relate this to other physical phenomena.
    Background
    As the rings rotate, their form distorts, growing wider around the center and flattening at the top and bottom. Interestingly, this is not due to a true outward force acting on the metal at this point, but is an artifact of its rotating reference frame and the forces acting to keep it moving in a circle. This is often termed a centrifugal reaction or centrifugal force, though it is technically a pseudo-force arising from the reference frame.

    This effect is seen in astronomy and geography, as rotating planets, stars, and other bodies take on similarly oblate spheroidal forms.
    D1

  • D3-01 MASSES SLIDING ON ROTATING CROSSARM

    D3-01
    Illustrates conservation of angular momentum
    Two masses which can slide along a crossarm can be moved to smaller radii by pulling on the chain hanging down through the center of the apparatus. With the masses at the largest radius, start the system rotating. Pulling the chain pulls the masses inward, reducing the moment of inertia and causing the system to rotate with a greater angular velocity. Conversely, slowly releasing the chain increases the moment of inertia and thus reduces the angular velocity.
    D3

  • I2-06 THERMOPILE WITH AUDIO OSCILLATOR

    I2-06
    Observe infrared radiation
    The output from a commercial thermopile is connected to an audio oscillator (as in N1-05) such that the frequency of the oscillator is proportional to the temperature observed: the hotter the object the higher the pitch. Use various sources: ice, boiling water, liquid nitrogen, the floor, people, etc. This is only qualitative; the system is not calibrated.
    N1, I2, PS1

  • I2-41: CONVECTION - POWDER IN WATER

    I2-41
    Illustrate convection.

    Heat one side of the tube, and the water will rise on that side by convection, carrying the powder, which makes the convection visible. To avoid overheating and destroying the apparatus, heat only for about ten seconds in a blast. Before beginning, rotate the entire apparatus so that the powder is uniformly distributed.

    A video camera may used to enlarge the action in the lecture halls.

    Background:

    The isolated heat source produces convection currents through the apparatus. Heated water rises up one side of the loop, drawing powder with it, while cooler water is drawn down the other side.
    I2

    i2-41a

  • I2-44: CONVECTION - CANDLE IN CYLINDER

    I2-44
    Demonstrate the mechanism of convection.
    A lighted candle lowered into the graduated cylinder goes out quickly because the buildup of gaseous products of combustion at the bottom of the tube prevents it from getting oxygen. Lowering the smaller tube into the larger graduated cylinder just above the candle flame separates the rising hot air from the falling cold air, allowing convection currents to feed oxygen to the candle flame.
    I2

  • I4-51: SUBLIMATION OF DRY ICE - PROJECTION

    I4-51
    Demonstrate sublimation of carbon dioxide (dry ice) from a solid into a gas.
    Place a chunk of dry ice on the plastic sheet, on an overhead projector if desired. As the dry ice evaporates (evaporation sublimation) it becomes smaller but leaves no residue.
    I4, I0

  • J1-06: FUN-FLY-STICK

    J1-06
    Demonstrates electrostatic fundamentals
    This is a battery operated static electricity generator that allows you to float tinsel shapes above the electrically charged stick. Since like charges repel each other, the negatively charged tinsel floats above the negatively charged stick.
    J1b

  • J1-24 ELECTROSTATIC HAIR RAISING

    J1-24
    Demonstrates electrostatic repulsion
    While standing on a large styrofoam insulating block, touch your hands to the top of the Van de Graaff dome, then have someone turn it on. The fact that your hair stands on end is a result of the repulsion between charges of the same sign that collect on your hair.
    J1a, OS2

  • J1-25 VAN DE GRAAFF - TRAINED RABBIT

    J1-25
    Demonstrates electrostatic repulsion
    A piece of fur, the "rabbit," is placed on top of the Van de Graaff dome, and a grounded point is held adjacent to the dome as the Van de Graaff is turned on. Pull the point back, allowing the dome and fur to charge, while ordering the rabbit to "sit up." Move the point closer to the dome while ordering the rabbit to "sit down."
    J1a, J1b

  • J1-26 VAN DE GRAAFF - REPULSION OF PIE PANS

    J1-26
    Demonstrates electrostatic repulsion

    A group of aluminum pie pans is placed on top of the Van de Graaff dome and the Van de Graaff is turned on. The pie pans are pushed off the top of the dome one at a time by the electrostatic repulsion. Use this as a way to argue that electrostatic forces might be stronger than gravitational forces.

    Engagement Suggestion:
    • Before turning the generator on, encourage students to predict what is going to happen. Challenge them to explain their hypotheses in terms of what they have learned about the behaviour of electrical charge.
    • Feel free to invite students to collect the scattered pans, but remind them not to get close to the Van de Graaff while it is turned on.
    J1a

  • J5-03: MAGNETIC FIELD OF A BAR MAGNET - 3D VERSION

    J5-03
    Three-dimensional field visualization of magnetic field of bar magnet.
    A cylindrical bar magnet is inserted into the center of a cube filled with a suspension of magnetic powder. When the device is shaked, mixing the magnetic powder uniformly through the liquid, and the magnet inserted, the powder lines up along field lines, allowing three-dimensional visualization of the field of a bar magnet.
    J5

  • J5-04: MAGNETS

    J5-04
    Show various magnets
    A varied collection of magnets is presented, including bar magnets, horseshoe magnets, disc magnets, ring magnets, and rare earth magnets. Ask about other types of magnets.
    J5

  • J5-06 MAGNET - BROKEN BUT NO MONOPOLE

    J5-06
    Demonstrates that magnet poles come in pairs
    The magnetic field of a bar magnet is demonstrated using iron filings on an overhead projector. The magnet is then broken and the demonstration is repeated. Each half of the original magnet has both poles
    J5

  • K1-02: FORCE BETWEEN CURRENT-CARRYING WIRES - PROJECTION

    K1-02
    Demonstrates the force between two adjacent parallel current-carrying wires
    A pair of wires are mounted in an overhead projectual, as seen without any current flowing in the photograph above. The projectual can be wired to carry parallel currents or antiparallel currents. Connect power supply to the desired wires, one set at a time. With the red and black connectors (at right in the photo above) hooked up in series, the current will be antiparallel. With a shunt joining those two connectors, the two wires can be run in parallel, with one cable connected to each end.

    Students should clearly see that parallel currents attract and antiparallel currents repel.

    Note that it is very important not to run the power for more than a second, less if possible! The device can easily overheat and be damaged.
    J/K

  • K1-04: FORCE ON CURRENT IN MAGNETIC FIELD - PORTABLE

    K1-04
    Demonstrate the force on a current-carrying wire in a magnetic field.

    A wire is placed or held between the poles of a small horseshoe magnet. When the ends of the wire are connected to a 6-volt battery, the wire jumps out of the magnet. The current in the wire or the orientation of the magnet can be changed to investigate the directions of the vectors involved.
    Engagement Suggestion
    • Once students have seen what happens, encourage them to predict the results of reversing the direction of the flow of current. Then swap it around and show what happens. Have them discuss the results.
    • What if you flip the magnet itself over? Again, have them predict what will happen, then try the experiment and discuss.
    Background

    This illustrates the Lorentz force, or Laplace force, as predicted by Maxwell’s equations. A current flowing through a magnetic field experiences a force determined by the cross product of the current vector and the magnetic field.


    See demonstration K1-03 in this section for a larger version of this demonstration for classrooms.

  • K2-01 EARTH INDUCTOR

    K2-01
    Induces an emf by moving a coil through Earth's magnetic field
    A large wire coil is connected to a projection galvanometer. Motion of the coil through the magnetic field of the earth induces an emf which is indicated on the meter. Alignment of the coil relative to the earth's magnetic field lines can be found which produces a maximum deflection of the coil, or almost no deflection. Optionally, a bar magnet (available upon request) can be thrust in and out of the coil to induce a larger voltage, illustrating the relatively low strength of the Earth's field.
    K2

  • K2-03 FARADAY'S EXPERIMENT ON INDUCTION

    K2-03
    Demonstrates the induction between two coils
    A primary coil is connected to a battery by a key switch, so that closing the switch causes current to flow in the coil and releasing the switch stops the current. Three secondary coils are connected in series with a galvenometer. The primary coil is positioned inside the secondary coil and the current in the primary turned on and off. When the current in the primary coil is turned on, a sharp spike of current appears in the secondary coil. There is no secondary current while the current in the primary remains on at a constant level. When the key is released the current in the primary coil ceases, creating a sharp current spike in the secondary coil of opposite sign to that produced when the primary current is started. The induced current is greater for a secondary coil with more turns. The experiment can be repeated with copper, aluminum, and iron cores. This uses the same coil and meter setup as K2-04; consider using them together to compare permanent magnets and electromagnetic coils.
    K2

  • K5-31 OHM'S LAW

    K5-31
    Demonstrates relationship between current, voltage, and resistance

    This simple circuit consists of a variable voltage power supply and a socket that can hold one of three modular resistor units, with a ammeter measuring the current through the resistor and a voltmeter measuring the voltage across the resistor. The whole circuit is mounted on a transparent plate that can be placed on an overhead transparency projector to show the wiring and the meters.

    The voltage can be varied to show how the voltage and current change together in a linear relationship to the resistance. Both two 1,000 Ohm resistors and one 2,000 Ohm resistor modules are available; the two 1,000 Ohm modules can be placed in parallel if desired.

    It can be valuable to ask students to make predictions about how the results will change when you change the resistance, then afterwards have them discuss their predictions and compare them to the results.
    K5

  • K6-23: HOT DOG COOKER - 110 VAC

    K6-23
    Illustrate the conversion of electrical energy into heat energy.
    A hot dog is mounted as shown in an overhead projection gizzit which skewers the hot dog between two nails connected to 110 VAC. The voltage applied to the hot dog and the current through the hot dog are displayed on the meters. The total energy can be found by plotting a graph of the current as a function of time and integrating. (Actually the current is pretty much constant so you can just take an average.) The initial and final temperatures are read by the digital thermometer, as seen in the photographs at the left and the right above. These pictures were taken using a fat-free vegetarian non-hot-dog. The cooking process is easier using a regular hot dog because the fat is an excellent electrical conductor. INSTRUCTOR MUST FURNISH ALL EDIBLE MATERIALS!!! Be sure to put the hot dog in the protective plastic shield provided so that grease will not splatter over the entire apparatus.