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Scientific Measurements. “measurement” could be defined as the process or the result of determining the magnitude of a quantity. Measurements can be made for length, volume, mass and time Different instruments are used depending on how accurate you want your measurement to be.
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Scientific Measurements • “measurement” could be defined as the process or the result of determining the magnitude of a quantity. • Measurements can be made for length, volume, mass and time • Different instruments are used depending on how accurate you want your measurement to be
Parts of a Measurement • The value (numerical portion) • The unit (describes what units) • The name of substance being measured EX: 1 teaspoon salt 2 liters of pop
Accuracy and Precision (uncertainty in measurements) • When recording a measurement: • Need to know how many digits should be recorded • are an estimated amount, they are not 100% exact • --are only as good as the instrument used to make the measurement • -
Uncertainty in Measurement • All measurements have a certain degree of uncertainty • No matter how careful you are • No matter how carefully you read the measuring instrument • No measurement is perfectly accurate • The quality of our measurements are stated in terms of accuracy and precision
Uncertainty in Measurements • Accuracy: how closed the measurement is to the reference value • Precision: How close repeated measurements are to each other
Accuracy = of a measurement is how close that measurement is to the true or “exact” value 100 g 100.3 g 100.03 g 100.032g The value with most decimal places would be considered the most accurate. The measurements are very precise (close to each other) even though four different balances were used.
Accuracy • Also subject to the reliability of the measuring instrument • The smaller the increments of units on the instrument, the more accurate
Precision • Refers to both the instruments and your ability to make reproducible or repetitive measurements of the same quantity.
Precision versus Accuracy Precise but inaccurate Precise and accurate It is also possible to have an accurate measurement without being precise. Imprecise and inaccurate
“Accuracy is telling the truth….. Precision is telling the same story over and over again.” Yiding Wang email@example.com
Strive for measurements that are accurate and precise Measurements you perform will be used in subsequent calculations In scientific measurements all the digits known w/certainty, plus the one estimated digit, are known as significant figures or significant digits. Significant Figures
Significant figures or Significant digits • ANY numbers generated by means of a measurement (length, volume, time, etc) should be expressed in the correct number of significant figures. • This reflects how close the measured values are to the true values.
Significant Figures Significant figures: is defined to be all digits in a number representing data or results that are known with certainty plus the first uncertain digit. 5.4 cm 7 0 1 2 3 5 8 4 6 9 10 cm 5.48 cm 7 0 1 2 3 5 8 4 6 9 10 cm