Measurements

LengthVolume

TemperatureMass

1.Will learn to use different measuring instrument2.Will learn that the smaller the unit increment, the more accurate your measurement will be3.Will learn the difference between measurements that are accurate and those that are precise4.Will learn to record measurements in the correct number of digits.

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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 salt2 liters of pop

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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

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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

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•Accuracy: how closed the measurement is to the reference value

•Precision: How close repeated measurements are to each other

Uncertainty in Measurements

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Accuracy

= of a measurement is how close that measurement is to the true or “exact” value

EX: Standard weight = 5.00g4.98g more accurate than 5.12 g

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Accuracy

• Also subject to the reliability of the measuring instrument

• The smaller the increments of units on the instrument, the more accurate

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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.

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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

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It is also possible to have an accurate

measurement without being

precise.

Imprecise andinaccurate

Precise andaccurate

Precise butinaccurate

Precision versus Accuracy

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“Accuracy is telling the truth…..

Precision is telling the same story over and over again.”

Yiding Wangyiang@mtu.edu

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• 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.

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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.

0 1 2 3 4 5 6 7 8 9 10 cm

5.48 cm

0 1 2 3 4 5 6 7 8 9 10 cm

5.4 cm

Significant Figures

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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 MeasurementsLab 3

Scientific MeasurementsPage 30

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Measurements With a Ruler orMeter Stick – Look at it FIRST! – Where is

“0”

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Protractor for Measuring Angles

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Measuring Angles Units are degrees (º)

Angle MeasurementsLab 3

Scientific MeasurementsPage 31

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Using a Vernier Caliperhttp://phoenix.phys.clemson.edu/labs/cupol/vernier/

•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.

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Parts of a Caliper

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• 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

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• 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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• 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.

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• 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.

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Practice Reading the Following Calipers

Measurement with a CaliperLab 3

Scientific MeasurementsPage 31