THE TEACHING OF PHYSICS 45

 (3) Use metric scale in drawing graphs and
 force (vector) diagrams.
 3. Emphasize its internal use.
 a. Basis of measure in all countries except U. S. A.
 and British Empire.
 b. In 1886 Congress set legal equivalents between
 U. S. and metric system.
 4. Show that because certain constants of water are
 taken as unity, conversion is made simple. Sp. gr. 1,
 density 1 g/cc, 1 calorie.
 5. Suggest memorization of length, weight, and vol-
 ume reduction units. 1 meter, 39.37 inches; or 1
 inch, 2.54 centimeters; 1 liter, 1.06 quarts; 1 kilo-
 gram, 2.2 pounds.
 6. Use charts and models freely to visualize these units.
C. Simplify mathematical operations to fit basic needs.
 1. Review simple seventh and eighth grade arithmetic
 as need is anticipated.
 Most needed review is in the four fundamental opera-
 tions, common and decimal fractions, ratio and pro-
 portion, percentage, finding area and volume, and
 square root.
 2. Formulas are extremely important but must have
 meaning.
 a. A teacher should learn where students have met
 the formulas in mathematics and general science
 and take advantage of the value of recall.
 b. Principle must be taught before formula is given.
 c. Some memorization must be done but in most
 cases recognition and choice of correct formula
 from posted list is sufficient.
D. Sell its everyday use by:
 1. General applications-show that physics teaches the
 principles underlying new developments in trans-
 portation, communication, and entertainment de-
 vices.