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Chapter 1

Chapter 1. In the quest to understand nature, scientists use physical quantities to describe the world around us. Physical Quantities, Units, Measurements and Estimation . A real life story… Gimli Glider. Nasa’s “Mars Climate Orbiter”.

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Chapter 1

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  1. Chapter 1 In the quest to understand nature, scientists use physical quantities to describe the world around us. Physical Quantities, Units, Measurements and Estimation

  2. A real life story… Gimli Glider

  3. Nasa’s “Mars Climate Orbiter”

  4. Two Teams, Two Measures Equaled One Lost Spacecraft (New York Times, October 1, 1999) Simple confusion over whether measurements were metric or not led to the loss of a $125 million spacecraft last week as it approached Mars, the National Aeronautics and Space Administration said on Thursday. An internal review team at NASA's Jet Propulsion Laboratory said in a preliminary conclusion that engineers at Lockheed Martin Corporation, which had built the spacecraft, specified certain measurements about the spacecraft's thrust in pounds, an English unit, but that NASA scientists thought the information was in the metric measurement of newtons. The resulting miscalculation, undetected for months as the craft was designed, built and launched, meant the craft, the Mars Climate Orbiter, was off course by about 60 miles as it approached Mars.

  5. Accuracy • refers to the degree to which an experimental result agrees with the expected value.

  6. Precision • different measuring instruments have different precisions. • -Ruler = 0.1 cm • -Vernier calipers = 0.01 cm • -Micrometer screw gauge = 0.001 cm

  7. Actual Height of Ms Tan = 1.59 m Precise but not accurate answer = 1.57 m Accurate and not precise answer = 1.6 m Accuracy & Precision

  8. Significant Figures Example 1: 7.12  1.23 x 12 = leave to lowest sf Example 2: 98.23 - 0.744 = leave to lowest d.p Example 3: (5.65 + 0.0547)  (0.11 x 5.4) = finally to 2 sf For multiplication and division For additional and subtraction Leave to 2 d.p Leave to 2 sf

  9. Using prefixes Speed of light = 300 000 000 m/s Size of atom = 0.000000000010 m Secret world.

  10. Prefixes

  11. Vernier caliper http://www.members.shaw.ca/ron.blond/Vern.APPLET/index.html

  12. Micrometer Screw Gauge http://www.members.shaw.ca/ron.blond/Micrometer.APPLET/index.html

  13. Zero Error vernier calipers When the two jaws of the vernier calipers touch each other, both zero marks on the main scale and on the vernier scale should coincide. If not, there is a zero error in the vernier calipers.

  14. Zero Error vernier calipers If the two jaws touch each other, but the zero marks of the main scale and vernier scale do not coincide as shown below, the zero error is positive. 0 1 main scale (fixed) vernier scale (movable) 5 0 10 zero error = +0.01 cm supposing observed reading is 3.24 cm, then corrected reading = observed reading – zero error = 3.24 – (+0.01) = 3.23 cm

  15. Zero Error vernier calipers If the two jaws touch each other, but the zero marks of the main scale and vernier scale do not coincide as shown below, the zero error is negative. 0 1 main scale (fixed) vernier scale (movable) 5 0 10 zero error = -0.02 cm supposing observed reading is 4.03 cm, then corrected reading = observed reading – zero error = 4.03 – (-0.02) = 4.05 cm

  16. Zero Error micrometer screw gauge Micrometers measure small diameters or thicknesses. anvil spindle sleeve thimble ratchet frame accuracy = 0.01 mm / 0.001 cm

  17. Zero Error micrometer screw gauge sleeve thimble reading on sleeve = 4.5 mm reading on thimble = 0.12 mm actual reading of object = 4.5 + 0.12 = 4.62 mm

  18. Zero Error micrometer screw gauge When the anvil and spindle of the micrometer touch each other, the scales should read zero. If not, there is a zero error in the micrometer.

  19. } 2 divisions Zero Error micrometer screw gauge If the anvil and spindle touch each other, but the scales do not read zero as shown below, the zero error is positive. supposing observed reading is 2.37 mm, then corrected reading = observed reading – zero error = 2.37 – (+0.02) = 2.35 mm

  20. Zero Error micrometer screw gauge If the anvil and spindle touch each other, but the scales do not read zero as shown below, the zero error is negative. } 3 divisions supposing observed reading is 2.87 mm, then corrected reading = observed reading – zero error = 2.87 – (-0.03) = 2.90 mm

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