Measurement

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Measurement

  1. 1. Measurement How much? How long? How many?
  2. 2. Exact and inexact numbers <ul><li>Exact number: </li></ul><ul><ul><li>A number with no uncertainty it </li></ul></ul><ul><ul><li>A dozen donuts, seven students, etc. </li></ul></ul><ul><li>Inexact number: </li></ul><ul><ul><li>A number that has a degree of uncertainty in it; results anytime a measurement is made </li></ul></ul><ul><ul><li>Height of student; temperature of student </li></ul></ul>
  3. 3. Precision and Accuracy <ul><li>Accuracy: </li></ul><ul><ul><li>How close a measured value is to the actual (true) value </li></ul></ul><ul><li>Precision: </li></ul><ul><ul><li>How close the measured values are to each other </li></ul></ul>
  4. 4. Testing our knowledge <ul><li>How accurate? </li></ul><ul><ul><li>Low accuracy </li></ul></ul><ul><li>How Precise? </li></ul><ul><ul><li>High precision </li></ul></ul>
  5. 5. Testing our knowledge <ul><li>How accurate? </li></ul><ul><ul><li>High accuracy </li></ul></ul><ul><li>How Precise? </li></ul><ul><ul><li>Low precision </li></ul></ul>
  6. 6. Testing our knowledge <ul><li>How accurate? </li></ul><ul><ul><li>High accuracy </li></ul></ul><ul><li>How Precise? </li></ul><ul><ul><li>High precision </li></ul></ul>
  7. 7. Systems of Measurement <ul><li>English: </li></ul><ul><ul><li>Commonly used in commerce and homes </li></ul></ul><ul><ul><ul><li>Inch, foot, pound, quart, and gallon </li></ul></ul></ul><ul><li>Metric system </li></ul><ul><ul><li>Used worldwide </li></ul></ul><ul><li>SI system </li></ul><ul><ul><li>Revised in 1960 with improved units </li></ul></ul><ul><ul><li>SI stands for “French Systeme International d’Unites” </li></ul></ul><ul><ul><li>Used by scientists </li></ul></ul>
  8. 8. SI System <ul><li>The Seven Base Units in the SI system: </li></ul>cd candela Luminous intensity A ampere Electric current m mole Amount of substance K kelvin Temperature s Second Time kg Kilogram Mass m Meter Length Unit Abbreviation Unit Name Base quantity
  9. 9. Metric system prefixes <ul><li>Common prefixes </li></ul><ul><li>For example, </li></ul><ul><ul><li>100 cm = 1 m </li></ul></ul><ul><ul><li>1,000 mg = 1 gm </li></ul></ul>1/1,000 m Milli 1/100 c Centi 1/10 d Deci 1,000 k Kilo
  10. 10. Length <ul><li>Meter is the SI base unit of length </li></ul><ul><ul><li>1 meter=1.05 yards </li></ul></ul><ul><ul><li>A dime is about 1 mm thick </li></ul></ul><ul><ul><ul><li>Or…1/1000 of a m </li></ul></ul></ul><ul><ul><li>Your little finger is about 1 cm across </li></ul></ul><ul><ul><ul><li>Or…1/100 of a m </li></ul></ul></ul>
  11. 11. Mass vs. Weight <ul><li>Mass </li></ul><ul><ul><li>A measure of the total quantity of matter in an object </li></ul></ul><ul><li>Weight </li></ul><ul><ul><li>A measure of the force exerted on an object by gravitational forces </li></ul></ul><ul><ul><li>If you weigh 60 kg on Earth, will you weigh more or less on the moon? Why? </li></ul></ul>
  12. 12. Mass vs. Weight <ul><li>How much does this astronaut floating in space weigh? </li></ul>What is the astronaut’s mass?
  13. 13. Mass <ul><li>Kilogram is the SI unit for mass </li></ul><ul><ul><li>Note that the prefixes are added to gram not kilogram, i.e., centigram, milligram, etc. </li></ul></ul><ul><ul><li>10 pennies weigh about 1 gram </li></ul></ul><ul><ul><ul><li>1 gram is 1/1,000 kilogram </li></ul></ul></ul><ul><ul><li>Aspirin commonly is 325 mg </li></ul></ul><ul><ul><ul><li>1 milligram = 1/1000 gram </li></ul></ul></ul>
  14. 14. Area and volume <ul><li>Area: measure of extent of a surface </li></ul><ul><ul><li>For a square, length vs width </li></ul></ul><ul><ul><ul><li>Square feet, ft 2 </li></ul></ul></ul><ul><ul><ul><li>Square cm, cm 2 </li></ul></ul></ul><ul><li>Volume: measure of the amount of space occupied by an object </li></ul><ul><ul><li>For a cube, side x side x side </li></ul></ul><ul><ul><ul><li>Cubic feet, ft 3 </li></ul></ul></ul><ul><ul><ul><li>Cubic cm, cm 3 </li></ul></ul></ul>
  15. 15. Volume <ul><li>Cubic meter (m 3 ) is the SI system base unit for volume </li></ul><ul><ul><li>A m 3 is too large to be used in the chemistry lab, so cm 3 is much more common </li></ul></ul><ul><ul><li>1 cubic cm (cm 3 )= 1 milliliter (ml) </li></ul></ul><ul><ul><li>1 liter is a volume equivalent to that of a cube that is </li></ul></ul><ul><ul><ul><li>10 cm x 10 cm x 10 cm or 1,000 cm 3 </li></ul></ul></ul>
  16. 16. SI Units <ul><li>The best way to understand SI units is to use them in everyday life </li></ul><ul><li>Everyday examples </li></ul>
  17. 17. Measuring volume <ul><li>Technique for measuring volume </li></ul>
  18. 18. Temperature <ul><li>A measure of the hotness or coldness of an object </li></ul><ul><li>Three scales: </li></ul><ul><ul><li>Kelvin </li></ul></ul><ul><ul><ul><li>after William Kelvin (1824-1907) </li></ul></ul></ul><ul><ul><ul><li>Does not use degree symbol </li></ul></ul></ul><ul><ul><li>Celsius </li></ul></ul><ul><ul><ul><li>After Anders Celsius (1701-1744) </li></ul></ul></ul><ul><ul><ul><li>Most commonly used in science </li></ul></ul></ul>
  19. 19. Three scales <ul><li>Kelvin </li></ul><ul><ul><li>after British mathematician and physicist, William Kelvin (1824-1907) </li></ul></ul><ul><ul><li>Does not use degree symbol </li></ul></ul><ul><ul><li>No negative numbers </li></ul></ul><ul><li>Celsius </li></ul><ul><ul><li>after Swedish astronomer, Anders Celsius (1701-1744) </li></ul></ul><ul><ul><li>Most commonly used in science </li></ul></ul><ul><li>Fahrenheit </li></ul><ul><ul><li>After German physicist, Gabriel Fahrenheit (1686-1736) </li></ul></ul><ul><ul><li>Based on the temperature of a salt-ice mixture as 0 °F and the boiling point of mercury at 600 °F </li></ul></ul>
  20. 20. Common temperatures <ul><li>Freezing point of water </li></ul><ul><ul><li>0 °C=32°F=273.15 K </li></ul></ul><ul><li>Room temperature </li></ul><ul><ul><li>22 °C=72°F=295 K </li></ul></ul><ul><li>Boiling point of water </li></ul><ul><ul><li>100 °C=212°F=373 K </li></ul></ul>

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