Academic journal article The Science Teacher

# Try This Tops Idea!

Academic journal article The Science Teacher

# Try This Tops Idea!

## Article excerpt

Make a slide rule ... adapted from FAR OUT MATH #43 by TOPS Learning Systems

1. Fold notebook paper in fourths. Cut off the lower quarters and fold them in half vertically.

2. Tape the strips, folded edges together, on your table. Number the lines (not spaces) in a doubling pattern up each fold, as shown.

3. Label the strips C and D. Circle 1 on C, and label the bottom line "index."

4. Lift up C and fold the tape under. Leave D taped to your table.

5. Compute 8 x 8 =64 on your slide rule: Move the index opposite 8 on the D-scale. Place a paper-clip hairline over 8 on the C-scale. Find 64 under the hairline on the D-scale.

6. Make up and solve multiplication problems, choosing numbers on your slide rule.

7. Write numbers on both scales as base-2 exponents, so each line has an exponent and equivalent number:

a. What does your slide rule add, and what does it multiply? Explain.

b. Tell how to use your slide rule to multiply. Use correct vocabulary.

OBJECTIVE

To make a slide rule. To understand how slide rules add and subtract exponents in order to multiply and divide numbers.

6. 8x64 = 512,4x32 = 128, etc.

7a. This slide rule adds equal distances numbered as base-2 exponents, thus multiplying equivalent numbers: Distances: 3 spaces [on DJ + 3 spaces [on C] = 6 spaces [on D] Base-2 Exponents: [2.sup.3 ]x [2.sup.3] = [2.sup.3+3] = [2.sup.6 ]Equivalent Numbers: 8 x 8 = 64

7b. (1) Slide the Index next to a number you want to multiply on the D-scale.

(2) Slide the hairline over the other number you want to multiply on the C-scale. …

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