Sara E. Thomas
After determining how the canoe and sailboat work students will be challenged to determine how the putt putt boat works. Students will be given materials to do a few smaller experiments relating to these principles.
What is the source of energy?
The putt putt boat does not have a rower like the canoe did, so where is the energy coming from? The energy is coming from the wax in the candle which is burning and providing heat to do work.
How is the heat doing work?
In order to understand the way our small model will work, students must understand phase changes. A phase change occurs when the molecules in one object reach a specific temperature which causes the molecules to change form. Phase changes go from solid to liquid to gas, or in reverse. Let’s take water, which when frozen is ice. If ice is heated to 32 degrees F then the molecules begin moving more quickly and they spread out, creating a liquid, or water. If water is then boiled at 212 degrees F the molecules begin to move even faster and the water will vaporize into steam, a gas. It is important that students understand these phase changes because our boat will be running because of the phase changes of water. The water in the metal piece is heated by the candle, and then it expands and becomes water vapor, a gas.
How does the phase change move the boat?
For our boat to work it will also be important that students understand that liquid and gas both travel from areas of high pressure to areas of low pressure. This can be demonstrated in a variety of ways to students. The air rushing out of a blown up balloon would be one, hot water rising to the top would be another (add food coloring to the hot water to show the obvious movement). The whole principle of our boat is that the heated water vapor must expand and then takes the path of least resistance to an area of lower pressure. The force of this steam moving out of the area of high pressure and into the area of water, low pressure, is what propels the boat forwards. (Fig. 4) Our small model is a simplified example of how a steam engine works. The invention of the steam engine revolutionized travel and communication.
History of the Steam Engine
The invention of the steam engine began back in the first century A.D. A Greek philosopher named Hero created an ‘aeolipile’ which worked on the same principle as a turbine; however Hero did not realize its potential to do work. His ‘aeolipile’ was a sphere which had two L shaped tubes on opposite sides of the sphere leading out of it in opposite directions. The sphere was filled with water, and then the water was heated. As the air above the water expanded it was forced out the tubes. Because of the positioning of the tubes the steam caused the ‘aeolipile’ to rotate (Fig. 5). Hero had discovered how to use heat to do work, however he did not realize it. (Storer 25)
Initially the steam engine was used to create a pump which would pump water out of mines. The engine used the principle of Hero’s ‘aeolipile’ to move water. Thomas Savery was the first to produce this type of pump. “In 1698 he patented his ‘engine’ for raising water ‘by the Impellent Force of Fire’” (Storer 35). The pump created a vacuum through the heating and cooling of air which caused the excess water to be sucked up and out of the mine shaft.
Another scientist named Newcomen used the same technology to move a piston which in turn moved a large wooden beam which moved the pump to pump out water (Storer 41). The next improvements came from James Watt who cut down drastically on the amount of water which needed to be heated, therefore reducing the amount of heat needed and increasing the efficiency. (Storer 52) It was not until later that the engines were used on machines for transportation.