1. Write a list of the sources of heat in the order of their importance to you. State why each is important to you.
2. Which three of the effects of heat do you make most use of? Explain what use you make of each of these effects.
3. Which of the forms of energy can be transformed into heat? How in each case?
4. Into what other forms of energy may heat be transformed? Name the device or process used in each case.
5. What five different commodities are purchased by people in your neighborhood for the production of heat? Which of these costs least for the amount of heat furnished? Which is most expensive? How do you determine these answers?
6. Why do many people buy heat in an expensive form, as in using an electric toaster, when they can obtain it in a cheaper form by burning gas or coal?
7. How many of the five effects of heat have you observed outside of school?
(2) Temperature and Expansion
141. Heat and Temperature.—We should now clearly distinguish between the terms, heat and temperature. Heat is a form of energy consisting of molecular motion. The temperature of a body is its degree of hotness. The amount of heat present in a body and its temperature are very different things. The temperature refers to the intensity of the heat in the body. A quart of water and a red hot iron ball may contain equal amounts of heat, although the ball has a much higher temperature than the water. A cup of boiling water will have the same temperature as a tank full of boiling water, but the tank will contain more heat. Every one knows that it will take longer to boil a kettle full of water than a cupful. A hot-water bag, holding 2 quarts of water will give off heat longer than a 1-quart bag, both being filled with water at the same temperature. To put it in another way, more work is done in heating a large amount of water, than a small amount through the same change of temperature.