Measurement and Precision

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Measurement and Precision

• Science 10

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SI (System International ) Units

• This system is used for scientific work around
  the world
• It is based on the metric system
• Includes
• - length ? metre (m)
• - volume ?litre (L)
• - mass ? grams (g)
• - time ? seconds (s)
• - temperature ?kelvin (K)
• (often Celsius is used for convenience and
  converted to K)

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• Precision to describe how well a group of
  measurements made of the same object or event
  under the same conditions actually do agree with
  one another.
• These points on the bulls eye are precise with
  one another but not accurate.

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• Accuracy represents the closeness of a
  measurement to the true value.
• Ex the bulls eye would be the true value, so
  these points are accurate.

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Lets use a golf analogy
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Accurate?
No
Precise?
Yes
7
Accurate?
Yes
Precise?
Yes
8
Precise?
No
Accurate?
No
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Readability

• The size of the smallest division on its scale
• Most metre sticks, for example, can be read down
  to millimetres, so the metre stick could be said
  to be readable to the nearest millimetre (mm)

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Estimating

• However, on most measuring scales, you can
  estimate readings between the lines if you look
  carefully.
• Scientists agree to add only one additional
  figure to their measurements in this way

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Significant Digits

• Because the precision of all measuring devices is
  limited, the number of digits for a measurement
  is also limited. The valid digits are called
  significant digits.

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• The ruler has 2 certain digits and we can
  estimate 1
• 9.40

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• The graduated cylinder has 2 certain digits
• and we can estimate 1
• 5.68

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Digital Measurements

• The last digit is assumed to be estimated
• Example
• ?digital balance
• ?4.75 g read on display
• ? the 5 is estimated

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• Precision and Measurement Activity
• ? Follow instructions at stations (1-4)
• ? Circle the estimated digit in all answers