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Lecture 1

Lecture 1. Dimensions and Units. Base Units. Length: meter (m) Mass: kilogram (kg) Time: second (s) Electric current: ampere (A) Amount of substance: mole (mol) Temperature: kelvin (K). http://physics.nist.gov/cuu/Units/current.html. Prefixes.

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Lecture 1

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  1. Lecture 1 Dimensions and Units

  2. Base Units • Length: meter (m) • Mass: kilogram (kg) • Time: second (s) • Electric current: ampere (A) • Amount of substance: mole (mol) • Temperature: kelvin (K) http://physics.nist.gov/cuu/Units/current.html

  3. Prefixes • http://physics.nist.gov/cuu/Units/prefixes.html

  4. Derived Units -- 1 • Speed/velocity • ms-1 • Acceleration • ms-2 • Force (Newton) • Use Newton’s 2nd law: F = ma • 1 N = 1 kgms-2

  5. Derived Units -- 2 • Pressure (pascal) (Pa) • Pressure = force per unit area • 1 Pa = 1 Nm-2 • Exercise: Reduce to base units

  6. Derived Units -- 3 • Energy/Work (joule) (J) • Work = force x distance • 1 J = 1 Nm • Exercise: Reduce to base units • Another approach – kinetic energy • KE = ½ mv2 • Unit: kg(ms-1)2 • (Another expression for 1 J)

  7. non-SI Pressure Units • Millibar (mb) • 1 mb = 100 Pa = 1 hPa (hectopascal) • Atmosphere (atm) • 1 atm = 1013.25 mb • Inches of mercury (in Hg)

  8. Inches of Mecury • Based on operation of a mercury barometer • Pressure is proportional to height of mercury column

  9. A “home-made” mercury barometer Height of column = 29.92 inches for a pressure of 1 atm

  10. Temperature Scales • Celsius scale (C) • Fahrenheit (F) • Kelvin (K)

  11. Celsius Scale • 0C = freezing point of pure water • 100C = boiling point of pure water at 1 atm

  12. Celsius and Fahrenheit

  13. Kelvin and Celsius • K = C + 273.15 • C = K – 273.15 0 K is called “absolute zero”

  14. Moles • 1 mole = an amount of atoms or molecules whose total mass equals the molecular weight of the substance in grams • Example: 1 mole of carbon 12 (C-12) is the number of atoms in 12 g of C-12

  15. Avogadro’s Number (NA) • NA = number of atoms or molecules in 1 mole • NA = 6.02 x 1023 mol-1 • Alternate definition of mole: amount of substance containing 6.02 x 1023 molecules

  16. HW Read Stull, Appendix A.

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