Measurement

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Chapter 1 Measurement
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• Measurement
• We measure things (such as weight, time, length,
  speed, etc.)
• We use tools (rulers, clocks, speedometers,
  etc.) to measure things
• Measurement tools are calibrated
• Calibration is in units (inches, seconds,
  pounds, mphs, etc.)
• Units require standards (conventional, habitual,
  customary)

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• Modern standards
• Not all quantities in nature are independent
  (e.g., speed is distance per time)
• Standards are created for independent (base)
  quantities length, time, mass, some other
• Modern day standards should be as invariable as
  possible
• Should be uniformly defined
• Should be accessible

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• SI (Systéme Internacional) most accepted
  international system of units
• Adopted in 1971
• Is commonly known as metric system
• Standard units are (there are more)
• 1 m (meter) for length
• 1 s (second) for time
• 1 kg (kilogram) for mass
• All other SI units are defined as derivatives of
  the base units (e.g., energy 1 J (Joule) 1 kg
  x 1 m2 / s2)

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• Length
• SI unit m (meter)
• Initially adopted as one ten-millionth of a
  distance between the North pole and the equator
  (standard platinum-iridium bar)
• Currently - a modern standard
• 1 m the length of the path traveled by light in
  vacuum during a time interval of 1/299 792 458 of
  a second

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• Time
• SI unit s (second)
• Historically
• 1 s 1 / 8640 day
• Currently - a modern standard
• 1 s the duration of 9,192,631,770 periods of
  the radiation corresponding to the transition
  between the two hyperfine levels of the ground
  state of the Cs133 atom

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• Time
• SI unit s (second)
• Historically
• 1 s 1 / 8640 day
• Currently - a modern standard
• 1 s the duration of 9,192,631,770 periods of
  the radiation corresponding to the transition
  between the two hyperfine levels of the ground
  state of the Cs133 atom

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• Mass
• SI unit kg (kilogram)
• Historically 1 kg
• mass of 1 liter of water
• Initially adopted in prototype of the kilogram
  was made of platinum-iridium and declared This
  prototype shall henceforth be considered to be
  the unit of mass
• Currently - an alternative modern standard
• 1 kg mass of C12 atom 1026 / 1.99264824
• (Dont confuse mass and weight 1 kg is the same
  on the Earth and on the Moon)

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Scientific notation 237 000 000 s 2.37 x
108 s 2.37 E8 s 0.0000664 m 6.64 x
10-5 m 6.64 E-5 m
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SI system prefixes
Examples 1.25E4 J 12.5 kJ 2.34 x 10-10 s
0.234 ns
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• Good SI web resource
• National Institute of Standards and Technology
  (NIST)
• http//physics.nist.gov/cuu/Units/

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• Conversion of units
• Need to know a conversion factor
• Use chain-link conversion
• (Check Appendix D for SI conversion factors)