US Customary Measurement System. O Keefe - LBHS

Transcription

1 US Customary Measurement System O Keefe - LBHS

2 The U S Customary System System of measurement used in the United States Similar to the British Imperial System of Measurement, but not identical Common U S Customary Units Measurement Symbol Unit length in. ft mi inch foot mile mass slug slug force lb pound time s second thermodynamic temperature F Fahrenheit degree

3 Common Items: Size Comparison

4 Recording Measurements A measurement always includes units A measurement always includes error A measurement is the best estimate of a quantity Scientists and engineers often use significant digits to indicate the uncertainty of a measurement Indicate the accuracy and precision of your measurement

5 Precision and Accuracy Precision (repeatability) = The degree to which repeated measurements show the same result Accuracy = The degree of closeness of measurements of a quantity to the actual (or accepted) value High Accuracy Low Precision Low Accuracy High Precision High Accuracy High Precision

6 Recording Measurements Ideally, a measurement device is both accurate and precise Accuracy is dependent on calibration to a standard Precision is dependent on the characteristics and/or capabilities of the measuring device and its use Record only to the precision to which you and your measuring device can measure

7 Significant Digits Accepted practice in science is to indicate uncertainty of measurement Significant digits are digits in a decimal number that carry meaning contributing to the uncertainty of the quantity The digits you record for a measurement are considered significant Include all certain digits in a measurement and one uncertain digit Note: Fractions are fuzzy numbers in which significant digits are not directly indicated

8 Recording Measurements General Rules Digital Instruments: Read and record all the numbers, including zeros after the decimal point, exactly as displayed Decimal Scaled Instruments: Record all digits that you can certainly determine from the scale markings and estimate one more digit Preferred over fractional scaled instruments Fractional Scaled Instruments: Need special consideration

9 Fractional Length Measurement A typical ruler provides A 12 inch graduated scale in US Customary units Each inch is graduated into smaller divisions, typically 1/16 increments

10 The Inch The divisions on the U S Customary units scale are easily identified by different sized markings. The largest markings on the scale identify the inch.

11 The Inch Each subsequently shorter tick mark indicates half of the distance between next longer tick marks. For example the next smaller tick mark indicates half of an inch = ½ inch 1/2

12 The Inch Half of a half = ¼ inch. An English scale shows ¼ inch and ¾ inch marks. All fractions must be reduced to lowest terms. 1/4 3/4

13 The Inch Half of a quarter = 1/8 inch 1/8 3/8 7/8 5/8

14 The Inch Half of an eighth = 1/16 inch 1/16 5/16 9/16 13/16 3/16 7/16 11/16 15/16

15 Measurement: Using a Fractional Scale How long is the rectangle? Let s look a little closer

16 Measurement: Using a Fractional Scale How long is the rectangle? What fraction of an inch does this mark represent? 3/16 1/4 1/2 1/8

17 Measurement: Using a Fractional Scale How long is the rectangle? What is the midpoint of 2 1/8 and 2 3/16? 5/32 1/8 3/16

18 Measurement: Using a Fractional Scale How do we determine that 5/32 is midway between 1/8 and 3/16? Convert each fraction to a common denominator: 32 Find the average of the two measurements 5

19 Recording a Measurement: Using a Fractional Scale How long is the rectangle? Remember the General Rule Fractional Scaled Instruments require special consideration Are 6 significant digits appropriate??? 1/16 in. =.0625 in.

20 Recording a Measurement: Using a Fractional Scale For the standard ruler marked in 1/16 inch increments (least count = 1/16 in.) Record fraction measurements to the nearest 1/32 inch 2 5 Record decimal equivalent to the nearest hundredths of an inch 2.16 in. Record with your data 32 in. The least count of the scale (1/16 in.) The increment to which measurements are estimated (nearest 1/32 in.)

21 Your Turn Record each measurement in fractional and decimal inches.