Scientific Measurements

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Scientific Measurements
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Two types of data

• Qualitative
• Measurements are descriptive and non-numerical
• Ex color, odor, texture

• Quantitative
• Measurements are numerical with a unit
• Ex length, volume, density

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Quantitative Data

• All measurements should contain 3 parts
• A numerical part (how big is the measurement?)
• A unit (did you measure that length in inches
  centimeters, miles???)
• An indication of precision

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Precision vs. Accuracy

• Precision is
• How close a series of measurements are to each
  other
• Use the same instrument to make a specific
  measurement several times

• Accuracy is
• How close a measurement is to a true or
  accepted value for whatever is being measured

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More on accuracy

• We evaluate the accuracy of a measurement by
  computing PERCENT ERROR
• error ?experimental accepted? x 100
• accepted
• (A percent error less than 5 is generally
  considered good, less than 1 is really good)

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Precision

• Precision is indicated using SIGNIFICANT FIGURES
• Sig figs are all digits, within a measurement,
  known with certainty plus one (and only one)
  estimated digit.
• Read between the lines!!!!

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Is it Significant or Not?

• All non-zeros are significant!
• Zeros between non-zeros are significant!
• Zeros at the end of a number are significant IF
  (and only if) the number contains a decimal point
• Zeros at the beginning of a number are NEVER
  significant.

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Calculations with measurements

• Addition/ Subtraction
• Add or subtract, then
• ROUND your answer to the least number of digits
  after the decimal in any of the measurements

• Multiplication/Division
• Multiply or divide, then
• ROUND your answer to the least number of sig figs
  in any of the measurements

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So, how do you round?
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2.1 Units of Measurement

• SI base unit(Systeme Internationale dUnites)-
  are base units scientists use to reproduce work
  of other scientists.There are 7 of these.
• Time- second (s)
• Length- meter (m)

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• Mass- kilogram (kg)
• Temperature- Kelvin(K)
• 5. Pressure- pascal (Pa)
• Derived unitsunit that is defined by a
  combination of base units
• 6. Volume- m3 or Liter(L)
• 7. Density-mass/volume
• gram/cm3 or gram/ml

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Scientific Notation

• Definition- expresses numbers as a multiple of
  two factors- a number between 1 and 10, and 10
  raised to a power, or exponent it makes it
  easier to handle extremely large or small
  measurements

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Rules

• If the number is gt 1 power of 10 or exponent is
  positive.
• If the number is lt 1 power of 10 or exponent is
  negative.

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Examples

• 14,670,000 in scientific notation is
• 1.467 x 107
• 0.0562 in scientific notation is
• 5.62 x 10-2
• Now you try!!!
• 1.392,000
• 0.000000028

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Multiplying in Scientific Notation

• You multiply the factors and
• Then add the exponents together
• Example
• (2x103) x (3x102)
• 2x3 6
• 325
• So 6x105

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Dividing in Scientific Notation

• You divide the factors and
• Then you subtract the exponents
• Example
• (9x108) divided by (3x10-4)
• 9 divided by 3 3
• 8 (-4)12
• So 3x1012

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Metric Units Of Measurement

• know the prefix, symbol, meaning , factor and
  scientific notation.

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Density

• Density is the ratio of the mass of an object to
  its volume.
• Try the following problem
• You have a block has dimensions 7.60cm X 1.85cm X
  2.05cm. Its mass is 27.092 g what is its
  density.
• Work on problems p.72. 25-29