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)

Prefixes

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

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

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

non-SI Pressure Units Millibar (mb) Millibar (mb) 1 mb = 100 Pa = 1 hPa (hectopascal) 1 mb = 100 Pa = 1 hPa (hectopascal) Atmosphere (atm) Atmosphere (atm) 1 atm = mb 1 atm = 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 = inches for a pressure of 1 atm

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

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

Celsius and Fahrenheit

Kelvin and Celsius K =  C  C = K – K is called “absolute zero” absolute zeroabsolute 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 (N A ) N A = number of atoms or molecules in 1 mole N A = 6.02 x mol -1 Alternate definition of mole: amount of substance containing 6.02 x molecules

HW Read Stull, Appendix A.