The opening theme of the co-requisite lecture course is Boltzmann's Vision of the Physical World.  Boltzmann is synonymous with that area of physics known as thermodynamics & statistical mechanics. To open the second semester of this hands-on course we will investigate the fundamental thermodynamic variables of pressure, volume & temperature, PVT-surfaces and a number of different types of thermometer.  Some basic thermal effects of three of four states of matter, phase changes among those states, and various thermodynamic processes (isovolumic, adiabatic) will also be experienced.  The transfer of thermal energy (heat) is involved all around.  The fundamental understanding of all of these concepts depend upon the existence of atoms.  The mindless random interactions of a very large number of atoms subject to the laws of mechanics (studied this past semester) forms the very foundations of thermodynamics & statistical mechanics.  Mindless, random interactions and large sample sizes suggest statistics and, yes, when you take into account the quantum nature of atoms, you have quantum statistical mechanics.  We'll take it slowly here and merely make observations that show that atoms exist.  We'll do that by repeating a famous experiment first recorded by the Scottish botanist Robert Brown.

In 1827 Robert Brown used a microscope to observe pollen spores suspended in water.  The pollen spores moved around in a random dance that at first suggested to Brown that he was observing tiny living creatures engaged in some sort of mating ritual.  We'll do essentially the same thing using smoke particles suspended in air.  I'll guarantee you that the particles are not alive.  How does this experiment demonstrate the existence of atoms (or molecules) that are in constant, random motion

a. A brass sphere cannot be inserted through a brass ring when both are at room temperature but can when the ring is heated to a sufficiently high temperature (or the sphere is sufficiently cooled.
b. A bimetallic strip curls one way when warmed and the opposite way when heated. Can make a "bimetallic" strip by cementing a strip of Scotch tape to a strip of aluminum foil.  How come a quarter doesn't curl up when you throw it in liquid nitrogen.
c. "Physics is Fun" jumping disk we used to study mechanics (WEP & CONE) consists of two thin layers of different metals laminated together.

We take advantage of the 77 K temperature of liquid nitrogen
a. to decrease the temperature of an inflated balloon producing a subsequent decrease in pressure,
b. to show the impressive insulating properties of Styrofoam by holding a Styrofoam cup filled with liquid nitrogen, and
c. to freeze a flower.
The superior insulating ability of a gas is demonstrated by pouring liquid nitrogen on your arm. The instant evaporation of the liquid provides protection from the 77 K temperature of the liquid nitrogen.

a. The calorie content of food is determined by burning the substance in a calorimeter and measuring the temperature rise of the calorimeter. Some foods are hard to burn because of the water content. A peanut burns easily and has an energy content of 1 kcal. Burning a peanut should raise the temperature of 1 kg of water 1 Co.
b. Outside the United States, there is a trend to express the energy content of foods in kilojoules rather than calories. We have a "Low Joule" Coca Cola can from Australia showing the energy content in kilojoules.  What's the conversion between calories & Joules?  ANS:  the mechanical equivalent of heat.

Normally water is made to boil by increasing the temperature which increases the internal pressure above the pressure above the liquid. Water can also be made to boil by decreasing the pressure above the liquid. In this demonstration water in a flask is brought to a boil by heating. The heat source is removed, boiling stops and the opening to the flask is sealed with a rubber stopper. Holding the neck of the flask in a stream of water reduces the pressure above the liquid and boiling can be observed.

CAUTION: Handle the flask with asbestos gloves.

Check out the cryophorus while you're at it.  You won't need the gloves unless you handle that end that you immerse in liquid nitrogen.

a. If you take two dissimilar wires and twist one end of each wire is bonded together then a voltage develops between the ends that are not twisted when the bonded end is heated. This arrangement is called a thermocouple. Two common types of thermocouples are labeled chromel-alumel and copper-constantan. The labels incorporate the names of the materials given to the wires. This demonstration shows the behavior of these two types of thermocouples.
b. A thermistor is a name given to a commercial temperature sensor whose resistance decreases when the temperature increases. Thermistors are often used in the sensitive element of thermometer used by nurses. This demonstration shows the behavior of a thermistor.
c. The resistance of a metallic  wire decreases when the temperature decreases. To show this a coil of many turns of  wire is available along with an ohm-meter and the ubiqitous vat of liquid nitrogen.  Check it out for yourself. At room temperature the resistance of the coil is so large that the bulb barely lights. When the coil is placed in liquid nitrogen the resistance of the coil decreases enough to make the bulb burn brightly.

OK, we're only going to provide equipment to investigate the first three.  It's up to you identify processes that are on-going within the room that are isothermal.  The things you need to investigate adiabatic, isovolumic and isobaric processes are lying around.  Identify them, then use them to demonstrate the appropriate effect  I'll help by demonstrating one of them for you.  Relate these processes to the PVT-surfaces.

 

This document was last modified on Tuesday, 26-Jan-1999 23:41:36 EST and has been accessed [an error occurred while processing this directive] times.  Please send comments and suggestions to:  marcumsd@muohio.edu