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Measurement

Measurement. How much? How long? How many?. Exact and inexact numbers. Exact number: A number with no uncertainty it A dozen donuts, seven students, etc. Inexact number: A number that has a degree of uncertainty in it; results anytime a measurement is made

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Measurement

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  1. Measurement How much? How long? How many?

  2. Exact and inexact numbers • Exact number: • A number with no uncertainty it • A dozen donuts, seven students, etc. • Inexact number: • A number that has a degree of uncertainty in it; results anytime a measurement is made • Height of student; temperature of student

  3. Precision and Accuracy • Accuracy: • How close a measured value is to the actual (true) value • Precision: • How close the measured values are to each other

  4. Testing our knowledge • How accurate? • Low accuracy • How Precise? • High precision

  5. Testing our knowledge • How accurate? • High accuracy • How Precise? • Low precision

  6. Testing our knowledge • How accurate? • High accuracy • How Precise? • High precision

  7. Systems of Measurement • English: • Commonly used in commerce and homes • Inch, foot, pound, quart, and gallon • Metric system • Used worldwide • SI system • Revised in 1960 with improved units • SI stands for “French Systeme International d’Unites” • Used by scientists

  8. SI System • The Seven Base Units in the SI system:

  9. Metric system prefixes • Common prefixes • For example, • 100 cm = 1 m • 1,000 mg = 1 gm

  10. Length • Meter is the SI base unit of length • 1 meter=1.05 yards • A dime is about 1 mm thick • Or…1/1000 of a m • Your little finger is about 1 cm across • Or…1/100 of a m

  11. Mass vs. Weight • Mass • A measure of the total quantity of matter in an object • Weight • A measure of the force exerted on an object by gravitational forces • If you weigh 60 kg on Earth, will you weigh more or less on the moon? Why?

  12. Mass vs. Weight • How much does this astronaut floating in space weigh? What is the astronaut’s mass?

  13. Mass • Kilogram is the SI unit for mass • Note that the prefixes are added to gram not kilogram, i.e., centigram, milligram, etc. • 10 pennies weigh about 1 gram • 1 gram is 1/1,000 kilogram • Aspirin commonly is 325 mg • 1 milligram = 1/1000 gram

  14. Area and volume • Area: measure of extent of a surface • For a square, length vs width • Square feet, ft2 • Square cm, cm2 • Volume: measure of the amount of space occupied by an object • For a cube, side x side x side • Cubic feet, ft3 • Cubic cm, cm3

  15. Volume • Cubic meter (m3) is the SI system base unit for volume • A m3 is too large to be used in the chemistry lab, so cm3 is much more common • 1 cubic cm (cm3 )= 1 milliliter (ml) • 1 liter is a volume equivalent to that of a cube that is • 10 cm x 10 cm x 10 cm or 1,000 cm3

  16. SI Units • The best way to understand SI units is to use them in everyday life • Everyday examples

  17. Measuring volume • Technique for measuring volume

  18. Temperature • A measure of the hotness or coldness of an object • Three scales: • Kelvin • after William Kelvin (1824-1907) • Does not use degree symbol • Celsius • After Anders Celsius (1701-1744) • Most commonly used in science

  19. Three scales • Kelvin • after British mathematician and physicist, William Kelvin (1824-1907) • Does not use degree symbol • No negative numbers • Celsius • after Swedish astronomer, Anders Celsius (1701-1744) • Most commonly used in science • Fahrenheit • After German physicist, Gabriel Fahrenheit (1686-1736) • Based on the temperature of a salt-ice mixture as 0°F and the boiling point of mercury at 600°F

  20. Common temperatures • Freezing point of water • 0°C=32°F=273.15 K • Room temperature • 22°C=72°F=295 K • Boiling point of water • 100°C=212°F=373 K

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