Measurement and Precision Science 10

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)

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.

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.

Let’s use a golf analogy

Accurate?No Precise?Yes

Accurate?Yes Precise?Yes

Precise?No Accurate?No

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)”

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

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.

The ruler has 2 certain digits and we can estimate

The graduated cylinder has 2 certain digits and we can estimate

Digital Measurements The last digit is assumed to be estimated Example:  digital balance  4.75 g read on display  the “5” is estimated

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