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PHYS105

  • C7-17 SUPERBALL

    C7-17
    Illustrates nearly elastic collisions
    Drop the superball and watch it bounce
    C7

  • C8-21: ROCK AND WASTE BASKET

    C8-21
    Demonstrate conservation of energy in a humorous way.
    Hold the rock up head high and drop it into the waste basket. Use the board to prevent damage to the floor. Have your students list all the possible types of work and energy involved, such as work done lifting the rock, gravitational potential energy, kinetic energy, heat, sound, and energy of deformation.
    OS1

  • C8-22: ENERGY CONVERSION - SUPERBALL AND SOUNDING BOARD

    C8-22
    Show transformation of energy from one form to another.
    Observe that the rebound of the superball is less when it is dropped on the metal shelving than when it is dropped onto a hard surface such as the floor. Discuss the possible forms of energy involved. Do the same experiment with a ping pong ball; describe and explain any differences.

  • H3-61 BEAKER BREAKER

    H3-61
    Breaks a glass beaker with sound

    An audio oscillator and 100 Watt power amplifier are used to drive a heavy-duty horn driver which is mounted in the back of the plastic beaker cavity with the sound emerging through a hole, which can be seen in the photograph. The beaker is positioned on a foam pedestal in front of the speaker hole. A microphone is mounted at 90 degrees from the position of the speaker.

    The beaker is marked with its primary resonant frequency, found in advance using digital spectrum analysis of a recording of the beaker ringing after being tapped. Most beakers have two possible resonant modes 45 degrees apart, due to the weight of the spout; the most effective technique is to drive the resonance with the spout facing directly away from the speaker. Set the frequency of the oscillator as shown on the beaker, with an amplitude of around 140mVpp. The oscilloscope will show two waveforms, the input signal and the signal picked up by the microphone. You may need to adjust the frequency slightly to account for changes in temperature or age since the beaker was tested; slowly shift the frequency by tenths or hundredths of a Hertz to find the amplitude peak (do not try to tune by watching for a displacement in the phase relationship, as there is a time delay between the signals introduced by the hardware). This done, set the strobe around 3000 cycles per minute, and adjust it until you can see the sides of the beaker flexing.

    This can be used to show the resonance of the beaker. You can also, optionally, shatter it, by increasing the input voltage at resonance. Be careful not to exceed 1Vpp.

    After the resonant frequency is found and the amplitude turned up, the oscillation of the beaker can be caused to exceed its elastic limit and thus to shatter. See the video links below to view a slow-motion video of the beaker at the moment it breaks.

    Engagement Suggestion
    • Show the students that there are two different resonant frequencies, and challenge them to develop theories of why this is.
    • Consider using this in conjunction with H3-62 to illustrate the effects of the beaker's spout in a more obvious (and quieter) manner.
    Background
    This process of driven resonance potentially leading to mechanical failure can be related to many engineering problems. This is an excellent opportunity to discuss how physics applies to real-world problems, like the Tacoma Narrows Bridge collapse.
    Also, be sure to explore our directory of oscillations and waves simulations to show other examples of complex mechanical oscillations.
    FS1, LS2, SU5

  • I1-63: HYDROGEN EXPLOSION

    I1-63
    Produce a hydrogen explosion

    A balloon filled with hydrogen is tethered about six feet above head level. The burning match on a stick is positioned under the balloon, creating the hydrogen explosion.
    Engagement Suggestion
    • One option for presenting this would be to compare the behaviour of two different balloons, hydrogen and helium. You can tell students what is in each balloon and have them make a prediction about what each will do, or show the demonstration first and then have students analyze why the results were different.
    I1, I0, FS1

    I1-63B

  • I2-04 WIEN'S LAW OF THERMAL RADIATION

    I2-04
    Shows that higher temperature blackbodies radiate with shorter wavelengths

    A variable transformer, or Variac, is connected to two identical incandescent light bulbs in parallel. These bulbs are viewed behind red and blue filters respectively. As the voltage is increased by the variac, the lights glow more brightly, and more light is seen through the blue filter relative to that of the red filter. Very little or no blue is seen at low voltages, whereas red is seen to be emitted even at very low voltages.

    Engagement Suggestion:
    • Ask students to compare this to other phenomena that emit light. Where else do you se this change of color with temperature?
    Background:

    Wilhelm Wien postulated in the 1890s that the power curve of blackbody radiation from an object could be computed from its temperature. His original calculations, obviously, did not take quantization into account; in modern practice, the revised calculations are still commonly referred to as Wien's Law.

    Note that this apparatus only works with incandescent lightbulbs. Fluorescent and LED bulbs do not produce their primary light through thermal excitation, and thus don't produce the same kind of blackbody spectrum.
    I2, PS1

  • 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

  • I2-22 THERMODYNAMICS BY TOUCH

    I2-22
    Demonstrates that touching a material tells something about its conductivity, not necessarily its temperature
    Various materials, all at room temperature, are arranged on a cart, and students are invited to touch them. The materials in order of increasing conductivity, are: styrofoam, wood, plastic, slate, steel, aluminum, and copper.
    I2

  • I2-27: THERMAL EQUILIBRIUM BETWEEN ALUMINUM AND COPPER

    I2-27
    Show process of thermal equilibrium happening between touching aluminum and copper cylinders.
    Pieces of copper and aluminum are held together by a large C-clamp. Small holes are drilled into the pieces to a allow a digital thermometer probe to be inserted to measure the temperature of each block, showing that the blocks are initially the same temperature, at equilibrium. Remove the thermometer probes and put a flame under one block to create a temperature difference. Remove the flame, reinsert the probes, and watch as the blocks come to thermal equilibrium.
    I2, I0, tools

  • I2-45: CONVECTION - HIGH/LOW CANDLES IN CYLINDER

    I2-45
    Brainteaser regarding convection.

    Two candles, one at the level of the table and one raised approximately 30 cm, are lit and then covered by a tube about 50 cm high and 10 cm in diameter. The tube is sealed at the top by a dark plastic cover to prevent air from flowing into the tube as the experiment progresses.

    Engagement Suggestion:
    • Encourage students to predict which candle will go out first, and why.
    • As the demonstration will typically take 2-4 minutes, discuss other related matters and then check in on the demonstration from time to time; ask students if it is behaving as they expected.
    • When both candles have gone out, ask students to discuss what they saw.
    Background:

    As the candles burn, the hot gases composing the products of combustion will be less dense than the cooler original air, and will rise to the top of the tube. The upper candle will therefore be extinguished sooner than the lower one.
    I2

    ii2-45ai2-45bi2-45ci2-45d

     

     

    Two candles, shown in the photograph at the left below, are lit and then covered by a plastic tube (sealed at the top), as seen in the photograph at the right below. In the apparatus as pictured the tube is about 50 cm tall and 10 cm in diameter, and the upper candle is about 30 cm from the bottom.

     

    i2 45 i2 45a

     

    After some period of time, as the oxygen in the tube is consumed by the candle flames, the candles will both cease to burn. The question involves the order in which the candles will go out.

    Which of the following statements is true?

     

     

    • (a) The top candle will go out first, then the bottom candle.
    • (b) The bottom candle will go out first, then the top candle.
    • (c) Both candles will go out at the same time.

     

  • 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

  • I5-11 ADIABATIC PROCESS - AIR PISTON WITH THERMISTOR

    I5-11
    Demonstrates adiabatic compression and expansion of air
    A thermister is enclosed in a small cylinder of air, the volume of which can be rapidly changed by moving a piston up and down. Pushing the piston down compresses the air, the air heats and the temperature increases, producing an increase in the resistance of the thermistor. Pulling the piston up expands the air adiabatically, the air cools and the temperature decreases, producing a decrease in the resistance of the thermistor. The thermistor is identical to those used in the thermometer probes of the old commercial digital thermometer.
    I5, I0

  • I5-31 STEAM ENGINE - STATIONARY

    I5-31
    Working model of a steam engine
    The engine can be attached to a weight hanging by a string over an axle which is connected to the engine through a series of gears.
    I5

  • J1-01 TRIBOELECTRICITY - CHARGING BY FRICTION

    J1-01
    Demonstrates "charging by friction"
    Rubbing silk on a glass rod makes the glass positive and the silk negative. Rubbing fur on a hard rubber rod makes the hard rubber negative and the fur positive. This effect is known as "triboelectricity," from the Greek "tribein," or to rub. The positively charged glass rod and the negatively charged hard rubber rod can then be used (1) simply to illustrate that electrical charge exists using an electroscope or (2) to perform other electrostatics experiments.
    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

  • J1-26 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

  • 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

  • K2-62 CAN SMASHER - ELECTROMAGNETIC

    K2-62
    Blasts a soda can into two pieces using electromagnetism

    A 400 microfarad capacitor is charged to 3000 volts (1.8 kilojoules) and discharged through a three-turn coil into which an aluminum soft drink can has been positioned. With the circular windows open, the two pieces of the can will be blasted over thirty feet to the sides of the large lecture hall. Charging the capacitor to less voltage results in a can with a "waist."

    This device can be explained in two distinct ways:
    (1) The rapidly rising current creates a rapidly rising magnetic field along the axis of the coil, which in turn induces an electric field going in circles inside the coil. The induced electric field causes an electron current in the can which experiences a vxB force in the magnetic field of the coil, causing the can to break into two pieces which are blown to the opposite sides of the lecture hall.
    (2) A type of "theta pinch" phenomenon. More information on this is available from Wikipedia. Another way to understand this is that the induced current around the can is opposite to the current in the primary coil, since it is opposing the change in flux. These concentric opposite currents repel each other, so the can is pinched and torn apart and ejected out the sides.

    This is an UNFORGETTABLE DEMONSTRATION. A must when you cover electromagnetism.

    This video, from the Video Encyclopedia of Physics Demonstrations, shows the operation of the can crusher with an animation illustrating (1) the electron current in the coil, (2) the vector magnetic field that it creates, (3) the induced electric field within the coil created as the coil current rapidly rises, (4) the electron current circling in the can created by that induced electric field, (5) and the vxB force on the electrons moving around the can.

    Following a description of the crusher electronic components, the animation is displayed. The animation may be stopped so that the directions can be studied in detail for the five (5) quantities listed above. Using the left hand rule (for electrons) the directions can be verified; note that according to Lenz's law the direction of the electron current induced in the can must be in the opposite direction to the electron current in the coil.

    Note that the magnetic field at either end of the coil possesses both an axial and a radial component; the electron current in the can is entirely azimuthal. Using the left hand rule to determine the direction of the cross product of the electron velocity and the magnetic field, it can be seen that the axial component of the magnetic field leads to an inward force, crushing the can, while the radial field component leads to an axial force, away from the plane of the coil at both ends of the can, causing the two parts of the can to move rapidly away from the coil. (In the large lecture hall the two parts of the can will be blown to the sides of the lecture hall.)

    The web site http://hibp.ecse.rpi.edu/Can_Crusher/home.html contains a drawing and animation showing how the RPI electromagnetic can crusher works.

    FS1

  • K4-07 BICYCLE GENERATOR

    K4-07
    Demonstrates a 110 VAC magnetoelectric generator, and the relationship of work to power output

    Pedaling the bicycle generates 110 VAC, which can be used to light an array of five 110 volt 150 watt lights. The sum, totaling 750 watts or about one horsepower when fully lit, can be verified using the voltmeter on the generator housing.
    K4, FS1

  • K4-09: BICYCLE GENERATOR - LIGHT BULBs VS CFLs

    K4-09
    Compare brightness and power requirements of regular tungsten filament light bulbs and compact fluorescent lamps.
    Pedaling the bicycle generates 110 VAC, which can be used to light an array of four 110 volt 60 watt incandescent light bulbs. The sum, totaling 240 watts when fully lit, can be verified using the voltmeter mounted on the bicycle. Alternatively, switch in the array of 15 watt CFLs (compact fluorescent lamps) and use the bicycle generator to light them. These CFLs are equivalent in light output to the 60 watt incandescent bulbs. It is easy to notice that the same amount of light created by the standard light bulbs can be created relatively easily using CFLs. The upper two photographs above show Krishna pumping the bicycle generator to light the incandescent bulbs (top photograph) and the CFL bulbs (second photograph); the lower two photographs show the arrays of lamps plugged into the 110 VAC outlet in front of the bicycle. The third photograph shows the incandescent bulbs and the last one shows the CFLs being activated. The student volunteer for riding the bicycle will testify as to the increased effort required to light the incandescents over the CFLs. This is a dramatic demonstration and can be used very effectively in class.
    K4, FS1