Measurements Length Volume Temperature Mass 1.Will learn to use different measuring instrument 2.Will learn that the smaller the unit increment, the more accurate your measurement will be 3.Will learn the difference between measurements that are accurate and those that are precise 4.Will learn to record measurements in the correct number of digits.

2 Parts of a Measurement 1.The value (numerical portion) 2.The unit (describes what units) 3.The name of substance being measured EX: 1 teaspoon salt 2 liters of pop

3 Measurements -are an estimated amount -a numerical value with attached units that expresses a physical quantity such as length, mass, volume, time or temperature -are only as good as the instrument used to make the measurement. Uncertainty in Measurement

4 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

5 Accuracy: how closed the measurement is to the reference value Precision: How close repeated measurements are to each other Uncertainty in Measurements

6 Accuracy = of a measurement is how close that measurement is to the true or “exact” value EX: Standard weight = 5.00g 4.98g more accurate than 5.12 g

7 Accuracy Also subject to the reliability of the measuring instrument The smaller the increments of units on the instrument, the more accurate

8 Length Measurements Ruler A has more uncertainty and gives less precise measurements. Ruler B has less uncertainty and gives more precise measurements. Measuring the length of a metal rod Metric Rulers for Measuring Length.

9 Precision Precision = making reproducible or repetitive measurements of the same quantity How fine the divisions are There will always be some uncertainty because of the limits in the accuracy of your instruments

10 It is also possible to have an accurate measurement without being precise. Imprecise and inaccurate Precise and accurate Precise but inaccurate Precision versus Accuracy

11 “Accuracy is telling the truth….. Precision is telling the same story over and over again.” Yiding Wang

12 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.

13 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 cm 5.48 cm cm 5.4 cm Significant Figures

14 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.

Length Measurements Lab 3 Scientific Measurements Page 30

16 Measurements With a Ruler or Meter Stick – Look at it FIRST! – Where is “0”

17 Protractor for Measuring Angles

18 Measuring Angles Units are degrees (º)

Angle Measurements Lab 3 Scientific Measurements Page 31

20 Using a Vernier Caliper / Used to accurately determine the fraction part of the least count division. Length of an object, the outer diameter (OD) of a round or cylindrical object, the inner diameter (ID) of a pipe, and the depth of a hole.

21 Parts of a Caliper

22 The caliper consists of a main scale engraved on a fixed ruler and an auxiliary caliper scale engraved on a movable jaw The movable auxiliary scale is free to slide along the length of the fixed ruler. The main scale is calibrated in centimeters with the smallest division in millimeters. The auxiliary scale has 10 divisions that cover the same distance as 9 divisions on the main scale. Therefore, the length of the auxiliary scale is 9.0 mm. Auxillary (Venier) Scale Main scale

23 When the caliper is closed and properly zeroed the first mark (zero) on the main scale is aligned with the first mark on the auxiliary scale. The last mark on the auxiliary scale will then coincide with the 9 mm-mark on the main scale. This is read 0.00 cm.

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26 Once the caliper is positioned to make a reading, make a note of where the first mark on the auxiliary scale falls on the main scale. We see that the object's length is between 1.2 cm and 1.3 cm because the first auxiliary mark is between these two values on the main scale.

27 The last digit (tenths of a millimeter) is found by noting which line on the auxiliary scale coincides with a mark on the main scale. The last digit is 3 because the third auxiliary mark lines up with a mark on the main scale. T The length of the object is 1.23 cm.

28 Practice Reading the Following Calipers

Measurement with a Caliper Lab 3 Scientific Measurements Page 31