The History of Measurement

1. The History of Measurement

2. Measurement • One of the steps of the scientific methods involves making observations. • An observation is information gathered by our five senses.

3. Types of Observations • There are two types of observations: • Qualitative Observations • Quantitative Observations

4. Qualitative Observations involve describing the properties of an object using words.

5. Examples of Qualitative Observations • The fire engine is red. • The fire engine is big. • The fire engine is shiny. • The fire engine has silver doors on the side.

6. Your Qualitative Observations • Make and record five Qualitative Observations about yourself.

7. Quantitative Observations • Quantitative Observations involve measurements. • A measurement includes a number and a unit.

8. Physical Properties The following physical properties can be measured: • Length • Width • Height • Mass • Temperature • Viscosity • Density • Etc.

9. History of Measurement • Objects were measured to aid commerce. • Many early measurements were based on body parts.

10. The Cubit • A cubit is the distance from your elbow to the tip of your middle finger.

11. Span • A span is the distance between the thumb and the little finger while the hand is outstretched.

12. Palm • A palm is the width of the closed hand.

13. Digit • A digit is the distance across the index finger.

14. Body Part Measurement Practice • Measure the following using the unit indicated: • Length of the room in: • Cubits • Spans • Length of the textbook in: • Digits • Palms • Spans • Cubits

15. Problems with Body Part Measurments • Body part measurements are not accurate when dealing with fractions of body parts. • People have different sized body parts. • The ratio of cubit to span may be different for different people.

16. Standard Systems of Measurement • Standard Systems are based on some standard to measure against. • Early standard systems often used body parts of the king or ruler as the standard distance. • When the king died, a new measurement system would be created.

17. Imperial System of Measurement • 1 foot = average length of a man’s foot • 1 yard = average length of a legionaire’s stride • 1 inch = width of a thumb

18. Imperial System Conversions • 12 inches = 1 foot • 3 feet = 1 yard • 1760 yards = 1 mile • 1 league = 3 miles • 6 feet = 1 fathom • 22 yards = 1 chain

19. How many inches in 2.5 leagues? 2.5 x 3 x 1760 x 3 x 12 =

20. The Metric System • In 1799, Napoleon commissioned a survey to find the length from the equator to the North Pole. • One ten-millionth of this distance was defined as a metre. • Conversions from one unit to another were all done by factors of 10.

21. SI Units of Measurement: The Seven Base Units

22. Your Quantitative Observations • Make and record 5 metric quantitative observations about yourself.

23. Accuracy and Precision • There are a number of ways that errors can be made during measurements. • The Accuracy of a measurement is how close the measurement is to the “true value.” • The Precision of a measurement is the number of digits in the measurement. • i.e. 1.78 m versus 1.781232243 m • The first is precise to three “Significant Digits” while the second is precise to 10 “Significant Digits.” • The smallest digit is 3 billionths of a metre, almost a thousand times smaller than width of a human hair.

24. Significant Digits • The significant digits in a number must indicate the precision of a measurement. • 250 kg has two significant digits as the zero may only be a placeholder. • 0.0250 kg has three significant digits. If we didn’t write down the zero on the right, the value would be the same. We must have written it down for a reason. • 205 kg has three significant digits. Zeros with other non-zero numbers on both sides must be part of the precision of the measurement. • Any time a zero is used as a placeholder, it is assumed not to be part of the accuracy. • 2.50 kg has three significant digits.

25. Scientific Notation • Scientific notation has a number been 1.0 and 9.999999999 that is multiplied by an exponent of 10. • kg has 3 significant digits.