SUBTOPIC: The Elements of the Ancients, Earth, Air, Fire and Water

OBJECTIVES:

The students will:

1) learn that a theory can be built using everyday observations and easy experiments

2) learn that the theory can be used to explain many new observations, and can also pose many questions that indicate the theory must be modified or perhaps replaced in order to progress further in our understanding of nature.

Empedocles, a Greek philosopher, was among the first to make sense of the seemingly infinite forms of matter. The most familiar forms of matter of course are solids, liquids, gases, and fire. A close look and a little experimentation shows that most substances contain one or more of these forms. The most common forms of these materials are the elements earth, air, water and fire itself. Empedocles' theory explains that all material things comprise different arrangements of these four elements.

           1 class period

MATERIALS: LARGE ROUND-BOTTOMED FLASK, PAPER TOWELS, MATCHES

PROCEDURE:

1) Ask students to describe what the different objects around the room are made of.

2) Tell the students that you will prove that everything is made of a very few elements, thus enabling them to better understand the world.

3) Fill a large round-bottomed, thin walled flask with tap water. 

4) Give it to a student, along with some paper towels. Tell the student to keep the flask scrupulously dry on the outside.

5) Show the class a dry paper towel. This is a good example of matter.

6) Roll the paper towel in your hand and light the end with a match. When it is burning well, you can assure the class that is contains FIRE. At this time, everyone will see large flakes of carbon and ash falling to the floor. Tell the students that this is obviously EARTH. A large amount of choking fumes are also rising from the burning paper. These gases are AIR.

7) Lastly, start another rolled towel on fire and hold it under the flask that the student is holding. Water vapor will immediately form on the flask. Explain to the students that the moisture they feel is WATER which is contained in the paper towel.

8) Now, as an optional addition to the activity, you may describe any sample of matter as a mixture of various proportions of the elements. For example, alcohol must be composed of FIRE, WATER and AIR, because it burns without residue (EARTH) and a rock must be composed of pure EARTH, because it does not burn at all. Students will begin to point out a weaknesses in the theory. They will probably ask what FIRE is made of. Point out that while this is a very powerful theory which should stood the test of time for nearly 2000 years, many experiments and observations made since then have shown that this old theory is far too incomplete and must be modified to gain further knowledge of matter.

The Project Physics Course. Chapter 2, sect. 1, Chapter 7, sect. 1. New York: Holt, Rinehart and Winston, 1970.