Project 2.3 Freeze Hot Water and Cold Water

Options:

• Write a brief report on the Mpemba effect. Give possible reasons for this phenomenon.
• Investigate the Mpemba effect by testing the rates at which similar samples of hot and cold water freeze when placed in a freezer.

The Mpemba effect is named after a Tanzanian student who observed that hot water tends to freeze faster than cold water under the same conditions. He observed this while making ice cream and raised the question in 1969.

Project 2.4 Stirling & Other Engines

Options:

• Write a brief report (2 to 3 pages) the history, design and possible uses of Stirling engines.
• Build a model Stirling engine based on a test tube and some marbles.
• Write a report (1 to 2 pages) on the different types of model Stirling engines that can currently be purchased.
• Demonstrate the operation of a small internal combustion engine used in model airplanes – or small pieces of equipment such as lawn mowers or line trimmers.

Sterling Engines

A Stirling engine has a sealed cylinder with different temperatures at each end. The gas inside the engine (which is often air, helium, or hydrogen) is moved from the hot side to the cold side. When the gas is on the hot side it expands and pushes the piston in one direction. When it moves back to the cold side it contracts and moves the piston in the opposite direction.

In the 1970’s, when oil prices soared and appeared to continue to do so, Ford, GM, and

American Motors Corp. spent millions of dollars developing Stirling engines for cars. Ford even built a Stirling that could drive away from the curb (with relatively low power) twenty seconds after you turned the start key.