during vacuum cooling. Using calculations, demonstrate if
this claim is reasonable.
4 –173 A 1982 U.S. Department of Energy article (FS
#204) states that a leak of one drip of hot water per second
can cost $1.00 per month. Making reasonable assumptions
about the drop size and the unit cost of energy, determine if
this claim is reasonable.
4 –174 Polytropic Expansion of Air ExperimentThe expan-
sion on compression of a gas can be described by the poly-
tropic relation pvnc,where pis pressure,vis specific
volume,cis a constantand the exponent ndepends on the
thermodynamic process.In our experiment compressed air in
a steel pressure vessel is discharged to the atmosphere while
temperature and pressure measurements of the air inside the
vessel are recorded. There measurements, along with the first
law of thermodynamics, are used to produce the polytropic
exponent nfor the process. Obtain the polytropic exponent n
for the process using the video clip, the complete write-up,
and the data provided on the DVD accompanying this book.
4 –175 First Law of Thermodynamics—Lead Smashing
ExperimentThe first law of thermodynamicsis verified with
a lead smashing experiment. A small piece of lead, instru-
mented with a thermocouple, is smashed with two steel cylin-
ders. The cylinders are suspended by nylon chords and swing
as pendulums from opposite directions, simultaneously strik-
ing the lead. The loss in gravitational potential energy of the
cylinders is equated to the rise in internal energy of the lead.
Verify the first law of thermodynamics using the video clip,
the complete write-up, and the data provided on the DVD
accompanying this book.
4 –176 First Law of Thermodynamics—Friction Bearing
ExperimentThe first law of thermodynamicsis verified with a
friction bearing experiment. A copper friction bearing is
attached to one end of a wood shaft that is driven in rotation
with a falling weight turning a pulley attached to the shaft.
Friction causes the bearing to heat up. Data reduction analysis
accounts for gravitational potential energy, elastic potential
energy, translational and rotational kinetic energy, internal
energy, and heat loss from the bearing. Verify the first law of
thermodynamics using the video clip, the complete write-up,
and the data provided on the DVD accompanying this book.
4 –177 First Law of Thermodynamics—Copper Cold Work-
ing ExperimentThe first law of thermodynamicsis verified
again, but this time with a copper hinge calorimeter that is
“worked” by a swinging pendulum, which causes a rise in the
hinge temperature. The loss in potential energy of the pendu-
lum is equated to the rise in internal energy of the hinge, plus
218 | Thermodynamics
the heat unavoidably transferred into the hinge clamps. Verify
the first law of thermodynamics using the video clip, the
complete write-up, and the data provided on the DVD accom-
panying this book.
4 –178 First Law of Thermodynamics—Bicycle Braking
ExperimentThe first law of thermodynamicsis verified yet
again—this time with a bicycle. A bicycle front caliper brake is
removed and replaced with a lever-mounted,copper calorime-
ter friction pad.The calorimeter friction pad rubs on the front
tire, heats up, brings the bicycle to a stop, and verifies the first
law of thermodynamics. Used in the data reduction analysis
are aerodynamics dragand rolling friction,which are obtained
using bicycle coast-down data read into a cassette audio
recorder by the bicycle rider. Verify the first law of thermody-
namics using the video clip, the complete write-up, and the
data provided on the DVD accompanying this book.
4 –179 Specific Heat of Aluminum—Electric Calorimeter
ExperimentThe specific heat of aluminumis obtained with
an electric calorimeter. The design consists of two individual
calorimeters—each an assembly of 13 aluminum plates with
electric resistance heater wires laced in-between the plates.
The exterior surfaces of both calorimeters and the surround-
ing insulation are identical. However, the interior plates are
different—one calorimeter has solidinterior plates and the
other has perforatedinterior plates. By initially adjusting the
electrical power into each calorimeter the temperature-versus-
time curves for each calorimeter are matched. This curve
match allows cancellation of the unknown heat loss from each
calorimeter and cancellation of the unknown heater thermal
capacity to deliver an accurate specific heat value. Obtain the
specific heat of aluminum using the video clip, the complete
write-up, and the data provided on the DVD accompanying
this book.
4 –180 Specific Heat of Aluminum—Transient Cooling
ExperimentThe specific heat of aluminumis obtained with an
entirely different experiment than the one described in Prob.
4 –179. In the present experiment a hollow, aluminum cylinder
calorimeteris fitted with a plug forming a watertight cavity.
The calorimeter is heated with a hair drier and then allowed to
cool in still air. Two tests are performed: one with water in the
cavity and one without water in the cavity. Transient tempera-
ture measurements from the two tests give different cooling
rates characterized with Trendlinesin EXCEL. These Trend-
linesare used to compute the aluminum specific heat. Obtain
the specific heat of aluminum using the video clip, the com-
plete write-up, and the data provided on the DVD accompany-
ing this book.