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PHYS131

  • G1-60 CHAOS - TWO BIFILAR PENDULA

    G1-60
    Illustrates chaotic motion
    The two pendula are started into apparently identical oscillations, but their motion soon diverges. No matter how closely the motions of the two pendula are started, they eventually must undergo virtually total divergence.

    Eric Neumann has created an online simulation that can be used to model one of the legs of the pendulum. Try experimenting with the simulation as well, and see how sensitive it can be to its initial conditions. https://www.myphysicslab.com/pendulum/double-pendulum-en.html

    G1

  • 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

  • I3-14: MAGDEBURG HEMISPHERES

    I3-14
    Demonstrate force arising from the atmospheric pressure of air.
    A mechanical pump is used to evacuate the air from inside a pair of sealed hemispheres. Ropes on the two hemispheres allow two groups of students to attempt to pull the hemispheres apart against the force produced by the atmospheric air pressure. The hemispheres have a diameter of about 5 inches, thus requiring a force of over 250 pounds to separate them when fully evacuated. A safety restraint holds the two hemispheres so that if the pressure releases they will not separate entirely. Three students pulling on each rope may be able to separate the hemispheres.
    FS1

  • I3-15: MAGDEBURG HEMISPHERES - PORTABLE

    I3-15
    Demonstrate forces arising from atmospheric air pressure.
    About 40 pumps will adequately evacuate the hemispheres, and the vacuum will last about one minute. The hemispheres have a diameter of about 5 inches, thus requiring a force of over 250 pounds to separate them when fully evacuated. A safety restraint prevents the two hemispheres from separating entirely.
    I3

  • I5-22 FIRE SYRINGE

    I5-22
    Demonstrates heating air by compression

    This demonstration consists of a transparent cylinder with a flared base, and a plunger that can be pushed into it. A small (very small) piece of cotton is pushed into the bottom of the tube using the wire provided, and the plunger is sealed into the tube. The plunger is pushed down sharply, compressing and thereby heating the air within. The temperature rises high enough to ignite the cotton with a flash, which can be readily seen through the plastic tube.
    Engagement Suggestion
    • Consider inviting a volunteer from the audience to try the demonstration. This will require careful supervision, but is safe. Just ensure that the syringe isn't knocked off the table by an overenthusiastic student!
    • This demonstration works best with a very small amount of cotton to ignite, no more than a few millimeters at most. Consider showing the device with different amounts of cotton, and how the results change. Encourage students to discuss reasons for this.
    Background
    This demonstration illustrates that an essentially fixed mass of air will increase in temperature when its volume is reduced, i.e. it is heated when compressed. The fire syringe is a simple piston, and can be used to introduce a discussion of the use of pistons in engines.

    Consider using this demonstration in conjunction with both other thermodynamics demonstrations from section I5, and relating it back to general gas behaviour with demonstrations from section I3.
    I5

  • I6-01 GAS PRESSURE - MODEL

    I6-01
    Illustrates the molecular nature of gas pressure
    A vibrator motor is activated causing chaotic motion of a group of ball bearings in a clear plastic container. The upward motion of the ball bearings pushes a black plastic plate upward, indicating the upward force of "air pressure" on the plate. Increasing the speed of the motor by turning up the variac increases the average speed of the balls and pushes the plate up further, modeling a greater pressure.
    I6, PW1

  • I6-25: DIFFUSION - DISTRIBUTION OF PING PONG BALLS

    I6-25
    Demonstrate on a macroscopic scale using ping pong balls how random molecular motion causes substances to diffuse.

    This model consists of a wooden frame with clear plastic covers, about one ping pong ball in width, ten bins at the top and bottom for setting up initial and analyzing final distributions, with several rows of pegs in between. When the horizontal plastic baffle holding the balls at the top is pulled away, balls will drop through the peg array, become randomly scattered, and drop into bins at the bottom.
    Engagement Suggestions
    • Put four orange balls into bin 5 and four white balls into each of bins 3, 4, 6, and 7. Challenge students to predict whether they will keep this same arrangement as they fall. (When the balls reach the bottom, the four orange balls will have become distributed into the white balls.)
    Background
    This shows on a larger scale how random molecular motion causes substances to diffuse. The array of fallen balls will approximate a probability curve; this is an opportunity to introduce statistical concepts in a physical, measurable manner.

    i6-25a

  • I6-26: DIFFUSION - PERFUME

    I6-26
    Illustrate diffusion.
    Spray the perfume into the air and the students soon notice the fragrance of the perfume. Point out that the perfume fragrance spreads through the room due to diffusion. Be sure to point out that there may be other reasons why the fragrance spreads, such as air currents.

  • 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

  • J1-03 KILOVOLT CARPET

    J1-03
    Demonstrates "charging by friction"
    Connect one end of the fluorescent tube to the grounded cable. Hold the other end of the tube as you scuff your shoes on the carpet.
    J1b

    J1-03-KILOVOLT-CARPET

  • J1-05 CHARGED BALLOONS

    J1-05
    Demonstrates "charging by friction"
    Rub a balloon on your clothing to give it electrical charge, then stick it on the blackboard, wall, etc. This is essentially the same triboelectric effect as J1-01, but with materials more familiar to students.

    Note that the backplane shown in the photo is for illustrative purposes; most classrooms have walls that work just fine.
    J1b

  • 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

  • J1-11 ELECTROPHORUS

    J1-11
    Demonstrates an electrophorus
    An electrophorus is a device which retains its charge so that it can act as a continuing source of charge for experiments. Charge the acrylic electrophorus plate negative by rubbing it with fur. Placing the aluminum plate on top of the plastic plate and grounding it charges the aluminum positive by induction. Existence of these charges can be verified using the electroscope. The charge remains on the surface of the plastic plate, so the aluminum plate can be charged by induction a number of times before the charge on the plastic leaks away
    J1b

  • J1-12: INDUCTION - ELECTROSCOPE

    J1-12
    Demonstrate charging by induction.
    A charged rod (black rubber in the photograph is negative) is held near the top plate of the electroscope, causing the electroscope to deflect. While the rod is in this position, the plate is touched by a grounded banana wire, and the electroscope returns to the uncharged position. When the charged rod is pulled away, the electroscope is charged positive, and deflects. This experiment can also be done using a positive glass rod to charge the electroscope negative by induction. The sign of the charge on the electroscope can be checked as follows: a rod with the same charge as the electroscope will cause further deflection of the electroscope when held close to the top plate, but a rod with charge opposite that of the electroscope will cause less deflection of the electroscope when brought close to the plate.
    J1b

  • J1-21 ELECTROSTATIC ATTRAC AND REPULS - CHARGED CYLINDERS

    J1-21
    Demonstrates electrostatic attraction and repulsion
    Charge the glass cylinders positive by rubbing with silk, and charge the hard rubber cylinder negative by rubbing with fur. The two positive glass cylinders repel each other, but both are attracted to the negative hard rubber cylinder.
    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

  • J3-01: EXISTENCE OF ELECTRIC FIELDS

    J3-01
    Demonstrate the existence of electric fields and to map them semi-quantitatively.
    A small conducting sphere on an insulating pole is connected electrically to an electroscope. The strength of the electric potential can be mapped out by observing the deflection of the electroscope as the metal ball sensor is moved about in the region of the Van de Graaff dome. After drawing a spark the electroscope must be grounded to reset it to neutral potential.
    J3a, J3b, LS1