8/26/10

Post date: Aug 26, 2010 12:44:13 PM

  • Operations with significant digits

    • Addition or subtraction

      • Round to the same decimal as the least precise measurement

      • e.g. 1.2 + 3.41 + 12.02 = ?

        • 1.2 is rounded to the tenths place, so answer must be rounded to tenths place

        • 1.2+3.41+12.02+0.002=16.632, but rounded to the tenths is 16.6

    • Multiplication or Division

      • Answer has same number of sig digs as the measurement with the fewest sig digs

      • e.g. 3.0 x 14.125

        • 3.0 has 2 sig digs, 14.125 has 5 sig digs, so answer must have 2 sig digs

        • 3.0 x 14.125 = 42.375

        • round to 2 sig digs, so answer is 42

    • Do page 25: 14-17

  • Factor-label for speeds

    • Speeds are always measured in (distance units) / (time units) (such as miles / hour or meter / second)

    • To convert these, simply convert either the distance or the time unit, then the other one

    • Be careful to place units correctly in conversion fractions that that unwanted units cancel

    • Units in calculations

      • treat units just like variables during calculations

      • units can multiply together, be squared, divide out, etc.

      • Examples:

        • 15 m / 5 sec = 3 m/sec

        • 3 ft x 4 ft = 12 ft^2

        • 25 N / 5 N = 5

  • Factor-label / sig dig extravaganza