PASCO TD-8592 SMALL PISTON HEAT ENGINE APPARATUS - Manual (Page 23)

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Small Piston Heat Engine 012-08375A
The Incredible Mass Lifter Engine Is Not So Simple
Understanding the stages of the engine cycle on a P-V diagram is reasonably straightforward. However, it is
difficult to use equations for adiabatic expansion and compression and the ideal gas law to determine the
temperature (and hence the internal energy of the air throughout the cycle. There are several reasons for this.
First, air is not an ideal gas. Second, the mass lifter engine is not well insulated and so the air that is warmed in
the hot reservoir transfers heat energy through the cylinder walls. Thus, the air in the can and in the cylinder are
probably not at the same temperature. Third, air does leak out around the piston, especially when larger masses
are added to the platform. This means that the number of moles of air decreases over time. You can observe
this by noting that in the transition from point d to point a, the piston can actually end up in a lower position
than it had at the beginning of the previous cycle. However, the Incredible Mass Lifter Engine does help us
understand typical stages of operation of a real heat engine.
➤ Note: The previous experiment was intended to help students consolidate the concepts of pressure and
volume by taking their own data for height and mass in each part of the cycle and then calculating the
pressures using the basic definition of pressure vs. force per unit area. An alternate method for doing this
experiment is to use the Science Workshop computer interface with the Pressure Sensor (CI-6532) in
conjunction with either a Motion Sensor (CI-6529) or Rotary Motion Sensor (CI-6538) to detect pressure,
volume, and height automatically with a computer.