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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

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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 yiang@mtu.edu**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

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