M0: Measurement

• Measurement

  • Quantitative observation consisting of two parts
  • number
  • scale (unit)
• physical quantity - name of unit - abbreviation

  • mass - kilogram - kg
  • length - meter - m
  • time - second - s
  • temperature - kelvin - K
  • electric current - ampere - A
  • amount of substance - mole - mol
• Uncertainty in Measurement

  • A digit that must be estimated is called uncertain.
  • A measurement always has some degree of uncertainty.
  • Record the certain digits and the first uncertain digit (the estimated number)
• Uncertainty in Measurement: Measurement of Volume of Liquids

  • The volume is read at the bottom of the liquid curve (meniscus).
  • Meniscus of the liquid occurs at about 20.15 mL.
• Uncertainty in Measurement: Precision and Accuracy

  • Accuracy: agreement of a particular value with the true value
  • Precision: degree of agreement among several measurements of the same quantity
• Significant Figures

  • Nonzero integers always count as significant figures. 3456 has 4 sig figs (significant figures).
• Significant Figures

  • Captive zeros are zeros between nonzero digits. These always count as significant figures. 16.07 has 4 sig figs
• Significant Figures

  • Trailing zeros are zeros at the right end of the number. They are significant only if the number contains a decimal point. 9.300 has 4 sig figs. 150 has 2 sig figs.
• Significant Figures

  • Exact numbers have an infinite number of significant figures. 1 inch = 2.54 cm, exactly. 9 pencils (obtained by counting).
  • Exact numbers do not limit the number of significant digits in a calculation