Follow

PHYS141

  • I3-43: TIRE PRESSURE - UNLOADED AND LOADED

    I3-43
    Show that tire pressure does not change when the tire is loaded within its normal operating limits.
    A gauge reads the air pressure in the tire. The tire can be loaded by someone sitting on the platform, causing the tire to flatten on the bottom because of the strain. Q: After the tire is loaded, will the pressure in the tire be (a) greater than, (b) less than, or (c) the same as, the pressure before being loaded. A: The pressure will stay the same. The flattening at the bottom, causing an apparent decrease in volume and increase in pressure, is compensated by slight bulging at all points around the tire.

  • I4-13: CHANGE OF STATE OF LN - POPPING CAN LID

    I4-13
    Show the increase in volume which accompanies the transition from liquid to gaseous nitrogen.
    Pour a small amount of liquid nitrogen into a can (typically under 10ml) and install the plastic lid. The liquid nitrogen heats up, changes to a gas, and forces the lid open.
    I4

  • I4-15 CONDENSATION OF STEAM - GALLON CAN COLLAPSE

    I4-15
    Illustrates forces produced by the pressure drop when steam condenses into water
    A small amount of water in the can is heated with the lid off, filling the can with steam. The can is then removed from the hot plate and the lid quickly screwed tightly thereon. Within a few seconds the steam begins to condense, creating a low pressure inside the can. The greater atmospheric pressure outside crushes the can.
    I0, SU14

  • I4-17: AIR BALLOON ON LIQUID NITROGEN

    I4-17
    Demonstrate dramatically that the volume of vapor is greater than the volume of the same amount of liquid.
    An air balloon is held on top of a liquid nitrogen bath. The volume of the air balloon decreases for two reasons: first, the volume of the gas shrinks according to Charles' law, and second, some of the air changes to liquid and shrinks considerably. Liquid nitrogen will readily cause oxygen to liquify, and even liquify some of the nitrogen in the balloon.
    I0

    i4-17a

  • I4-19: CONDENSATION OF STEAM - SODA CAN COLLAPSE

    I4-19
    Surprising demonstration using condensation of steam.
    A soda can with a small amount of water in the bottom is heated until the water boils, filling the can with steam. Very quickly the can is removed from the heater and inserted upside down into a container of cold water. The steam condenses so quickly that the can collapses, as seen in the photograph. This is quite a dramatic demonstration, and gets a good reaction from students.
    I4, I0, SU15

  • I4-31 ICE BOMB

    I4-31
    Demonstrates forces created by freezing water
    A pipe elbow with end caps is filled with water, sealed by tightening the ends, and dropped into a metal container of liquid nitrogen. Within about one minute the water freezes, expanding sufficiently to break the cast iron with a loud crack and a big cloud of vapor.
    I0, I4, SU5, OS6

  • I4-32: FREEZING WATER BY PUMPING

    I4-32
    Freeze water by reducing the ambient pressure.
    Place about four drops of water onto a cellophane "watchglass" in the vacuum chamber as in the photograph at the left. Evacuate the chamber with the vacuum pump. Almost immediately the water will begin to bubble (boil), as seen in the middle photograph below, and within about one minute the boiling will subside and the water will freeze. When the water freezes it is clearly seen to become opaque on the overhead projector screen, as seen in the photograph on the right below. This is a very dramatic demonstration.
    I4, I0

    i4-32ai4-32bi4-32c

  • I5-01 MECHANICAL EQUIVALENT OF HEAT - SHOT BAG

    I5-01
    Demonstrates that heat can be produced from mechanical work
    The temperature of lead shot in a shot bag is measured with the digital thermometer. The shot bag is then beat on the floor about ten times, and the temperature measured once again. The work done in beating the shot bag on the floor has been converted to heat. Not very much heat though: use the tenth degree scale for quicker results!
    I5, I0, tools

  • I5-03: MECHANICAL EQUIVALENT OF HEAT - JOULE'S METHOD

    I5-03
    Determine the mechanical equivalent of heat.
    Turning the handle with weights hanging from a cord wrapped around the copper cylinder requires a calculable amount of mechanical energy. This energy is converted into heat in the copper cylinder and the water bath, raising their temperature. The constant of proportional, which is the mechanical equivalent of heat, can be calculated using these two measurements. The device counts turns, so you can continue to lecture while cranking, typically 100-150 turns. The result is generally good to better than ten percent. (Note that when you turn the handle the heavy weight should be lifted off the floor, so the net frictional force causing the heating of the cylinder is the difference between the weights on the two ends of the cord.)
    I5, I0

    i5-03a

  • I5-15: ADIABATIC EXPANSION OF CARBON DIOXIDE

    I5-15
    Illustrate adiabatic cooling by producing dry ice
    Carbon dioxide, leaked slowly out of the fire extinguisher onto a black felt cloth, produces dry ice, which can be easily seen. Adiabatic expansion and cooling occur when the CO2 gas comes out of the nozzle under high pressure and expands in the atmosphere. Enough is produced to pass the cloth around the class so that students can feel that it is actually cold. This experiment is a bit more complicated than simple adiabatic expansion. The carbon dioxide actually exists in the fire extinguisher as a liquid, so that much of the cooling is due to the evaporation of the liquid CO2 before it is ejected from the nozzle.
    FS1

  • 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

  • I5-51: SPECIFIC HEAT - ALUMINUM AND COPPER

    I5-51
    Illustrate calorimitry and to determine experimentally the specific heats of aluminum and of copper.
    Boil the aluminum and copper blocks in a pan of water and place the metal blocks at 100 degrees C into equal amounts of water at room temperature in two styrofoam containers. Stir the water in the containers with the digital thermometer probe, measuring the temperature when equilibrium is reached. From these measurements the specific heats can be determined.

    Multiply the specific heat by the molar mass to find the molar specific heat. The values for both materials are nearly the same and equal to 3R=6(1/2)kT.
    I5, I0, ME1