Post-Laboratory Activities

Compare student answers. Have the students brainstorm within their groups to determine how they can come closer to the temperature of the hot water that was determined by direct measurement. Have a contest to see which group can modify their experimental procedures to come the closest to the temperature in the coffee urn as taken by direct measurement.

Assessing Laboratory Learning

1. Challenge students to design an experiment to determine the temperature of the hot water by melting a known quantity of ice. Encourage them to do it as a home project and share their plan with their parents/guardians.

2. Assume an industry dumps hot (120 °F) water into a river. Your are part of a team to assess the impact on thermal pollution. Identify some of the parameters you are interested in measuring for the study?

3. Ducks are able to keep warm blood flowing from their feet back to their bodies. Vessels that carry blood from the body lie next to vessels that carry blood from the internal organs. Explain how this arrangement warms the blood to the body in the duck.

History Extension Supporting Some Like It Hot

Rumford and the Theory of Heat

Our knowledge of how solids and liquids behave is closely tied to our understanding of the kinetic theory of matter. Kinetic theory concepts depend heavily upon the nature of heat and heat flow. Until the early to middle nineteenth century, heat was believed to be an invisible fluid known as caloric.

Caloric was thought to be squeezed out of little pockets in matter by the pressure of machines doing work on the surface of the matter. The influence of the caloric theory of heat can be seen yet today as heat is still said to Òflow,Ó and until very recently the accepted unit of heat was the calorie. Much of the experimental evidence which led the the overthrow of the caloric theory was collected by Count Rumford. Count Rumford, an American expatriate, was in charge of boring cannons for the Bavarian army. Rumford found that so much heat was released during the boring of cannons that a constant flow of water over the barrel of the cannon was necessary to keep the cannon from becoming too hot and warping as the boring drill was doing its job.

To RumfordÕs surprise the cannon barrels heated up more when the drills were dull and very little actual material was being removed by the boring process. He determined this by measuring the amount of water necessary to keep the cannon cooled when boring with dull versus recently sharpened drills.

In an ingenious leap of reasoning, Rumford concluded that heat could not possibly be a fluid trapped in pockets in the cannon barrel. He reasoned that if caloric were a fluid trapped in the material, more of this invisible fluid would be released during rapid drilling. The sharpened drill would be swiftly cutting into new Òpockets,Ó freeing the caloric.

The fact that a dull drill produced more heat was inconsistent with the caloric theory. Rumford concluded that the dull drill could not be cutting into enough pockets of caloric to release the tremendous amounts of heat measured. He correctly reasoned that heat was a form of energy released by the friction as the surfaces were rubbed together. His theory was not fully accepted until James Prescott Joule measured the mechanical equivalent of heat in a series of experiments conducted nearly 50 years later.