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Al Tobias (wat4y) - Office: Gibson S123 & Physics 218, (434) 924-0538

Physics Demo Manual

Demonstrations are cataloged according to PIRA Bibliography


Due to Physics Building renovations, the lead time to set up demo requests has increased due to the need to transport equipment across campus. Please be kind and let me know well ahead of time what you need.

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 Thermal Properties Of Matter
 Heat And The First Law
 Change Of State
 Kinetic Theory
 Gas Law
 Entropy And The Second Law
  video  - Reversible and Irreversible Processes
  video  - Stirling Engine
  video  - Steam Engine
 Heat Engines

 video  - Stirling Engine


To demonstrate the Stirling Engine cycle.


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  DEMO VIDEO DOWNLOAD w/ sound / 1920x1080 / 24.19Mb/s / 357MB size  

  DEMO VIDEO DOWNLOAD w/ sound / 854x480 / 5.69Mb/s / 86MB size  

We have two examples of Displacer type Stirling Engines, a PASCO Coffee Cup engine and a Boehm Gamma-type engine


The manual for this engine is here. This is a Displacer-type (Coffee Cup) Stirling engine. For some animations, check these sites: Place engine on top of a mug or beaker with a hot water in it. After few seconds, the engine will start operating. Or place it on cold reservoir, like container of ice water and it will rotate in the opposite direction.

Stirling Engine Model works as follows.

When the yellow foam inside the engine is near the top of the cylinder (and the engine is running on a cup of hot water) most of the air is on the hot side where it is heated. Air expands and pushes up on the piston connected to the flexible membrane. Since the piston and the yellow air displacer have 90deg offset, while piston still moves up foam displacer starts moving down to the bottom of the engine. Most of the air moves to the top colder side of the engine and cools. Air contracts and the piston starts moving down. While piston still moves down foam displacer begins moving up, most of the air moves to the bottom of the engine heats up and cycle repeats.

This engine would run even if the “displacer” was solid. It runs much better with the foam because it is acts like heat regenerator.

When the air is flowing from the hot side of the engine to the cold side it flows through and around the foam. Since the air is hotter than the foam, some of the heat is stored into the foam. When the air makes the return trip to the hot side of the engine it once again flows through and around the foam. This time the air is colder than the foam and absorbs back the heat stored in it.


The Boehm instruction manual is located here. This is a Gamma-type stirling engine where its displacer piston and power piston are housed in different cylinders, but both are attached to the same flywheel. The displacer piston is the one directly attached to the heated side of flywheel, while the power piston is on the opposite side but is still connected in the closed system.


Engine will need initial kick to start rotating.