Transcript 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 http://physics.nist.gov/cuu/Units/prefixes.html Derived Units -- 1 Speed/velocity ms-1 Acceleration ms-2 Force (Newton) Use Newton’s 2nd law: F = ma 1 N = 1 kgms-2 Derived Units -- 2 Pressure (pascal) (Pa) Pressure = force per unit area 1 Pa = 1 Nm-2 Exercise: Reduce to base units Derived Units -- 3 Energy/Work (joule) (J) Work = force x distance 1 J = 1 Nm Exercise: Reduce to base units Another approach – kinetic energy KE = ½ mv2 Unit: kg(ms-1)2 (Another expression for 1 J) 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) Inches of Mecury Based on operation of a mercury barometer Pressure is proportional to height of mercury column A “home-made” mercury barometer Height of column = 29.92 inches for a pressure of 1 atm Temperature Scales Celsius scale (C) Fahrenheit (F) Kelvin (K) Celsius Scale 0C = freezing point of pure water 100C = boiling point of pure water at 1 atm Celsius and Fahrenheit 9 F C 32 5 5 C F 32 9 Kelvin and Celsius K = C + 273.15 C = K – 273.15 0 K is called “absolute zero” 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 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 HW Read Stull, Appendix A.