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P Lab 06 Heat Engine Report

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Subject
Physics
School
Northern Virginia Community College
Type
Homework
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Physics 231
Physics with Video Analysis 24 -
1
A Heat Engine: Relating Work to the P-V Cycle
Figure 1: The PASCO scientific Heat Engine a.k.a. the
“incredible mass lifter.”
A Real-Time Heat Engine Cycle: A
canister filled with air is attached to a
cylinder with a piston as shown in Figure
1. When a mass is placed on top of the
piston it goes down a little bit. Then
when the canister is transferred from a
cold to hot water bath the piston and
mass rise as the engine transforms
thermal energy into mechanical work.
A Challenge: You have been studying your
textbook carefully and are trying to understand
how the work done by a heat engine can be
related to changes in the pressure, P, and
volume, V, of its working substance.
1
In
particular you would like to relate the work it
takes to lift a mass to the area enclosed by a P-
V diagram that describes what happens the
engine’s air – its working substance.
The relationship between these factors seems
weird and abstract. The goal of this assignment
is explore how the work done by an engine that
raises a 200 gram mass during each process of
its cycles is related to the area enclosed by its
P-V graph.
Figure 2: A P-V diagram for 1 cycle of the "incredible
mass lifter"
Review of Types of Heat Engine Transitions:
Transition
The Working Medium Undergoes:
Isothermal
No temperature change (T is constant)
Isobaric
No pressure change (P is constant)
Adiabatic
No thermal energy transfer to or from the working medium (Q = 0)
Isovolumetric (also called
Isochoric)
No volume change (V is constant)
Getting Started: Before answering the questions that follow you should open the Logger Pro file entitled
<HeatEngine.cmbl> with the movie <Mass-Lifter.mov> inserted in it. While the movie was made, the position
(y) of a sound-reflecting platform was recorded by an ultrasonic motion detector. At the same time a sensor
recorded the pressure, P, in the engine’s trapped air– its working substance. The movie and the sensor data
have been synchronized. If you click on the Replay button, you can examine a graph showing how y and P
1
All heat engines use a working substance that can expand or contract as it exchanges energy with its surroundings. In our PASCO engine the
working substance is the air trapped in a cylinder, hose, and canister.
P (KPa)
V
sys
(m
3
)
b
c
d
canister
tubing
piston
Sound
reflecting
platform
cylinder
with
trapped
air

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24 -
2
Physics with Video Analysis
1. Qualitative Considerations
(a) Four different events make the transitions in a single engine cycle happen. Using Insert>Shapes in Word,
draw a line between each transition and the event that causes it. Note: These transition points are marked
in Figure 2. 10 pts.
b c
d
a
Transition
Cause
a
b
• Mass is removed from the platform
b
c
• Chamber is moved to the hot reservoir
c
d
Chamber is moved to the cold
reservoir
d
a
• Mass is placed on the platform
(b) Which type of transition (isothermal, isobaric, adiabatic or isovolumetric) describes what happens when
the 200 g mass is placed on the platform so that it sinks quickly by a small amount? Explain. Hint: This
process occurs in a small fraction of a second, while the air, the system’s working medium, is
compressed reducing its volume and raising its temperature. 5 pts.
Adiabatic process due to the short fraction of time.
(c) Which type of transition (isothermal, isobaric, adiabatic, or isovolumetric) describes what happens when
the canister is moved from the cold water bath to the hot water bath. Explain. 5 pts.
Isovolumetric. This is because the volume of the canister remains Constant only the temperature and
pressure changes.
(d) Which type of transition (isothermal, isobaric, adiabatic, or isovolumetric) describes what happens when
the 200 g mass is removed from the platform so it rises very fast? Explain. Hint: This process is very
rapid and occurs in a small fraction of a second. 5 pts.
Isovolumetric as volume remains constant
(e) Which type of transition (isothermal, isobaric, adiabatic, or isovolumetric) describes what happens when
the canister is moved from the hot water to the cold water. Explain. 5 pts.
There is loss of energy when the canister is moved from the hot water to the cold water
hence the transition is obviously isovolumetric since volume doesnt change.

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Physics 231 A Heat Engine: Relating Work to the P-V Cycle piston tubing canister cylinder with trapped air Figure 1: The PASCO scientific Heat Engine a.k.a. the “incredible mass lifter.” A Real-Time Heat Engine Cycle: A canister filled with air is attached to a cylinder with a piston as shown in Figure 1. When a mass is placed on top of the piston it goes down a little bit. Then when the canister is transferred from a cold to hot water bath the piston and mass rise as the engine transforms thermal energy into mechanical work. A Challenge: You have been studying your textbook carefully and are trying to understand how the work done by a heat engine can be related to changes in the pressure, P, and volume, V, of its working substance.1 In particular you would like to relate the work it takes to lift a mass to the area enclosed by a PV diagram that describes what happens the engine’s air – its working substance. The relationship between these factors seems weird and abstract. The goal of this assignment is explore how the work done by an engine that raises a 200 gram mass during each process of its cycles is related to the area enclosed by its P-V graph. c b P (KPa) ...
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