Density

• Density


  • d = m/v (g/cm3 or g/mL)
  • Mass usually expressed in grams
  • Volume usually expressed in cm3 or ml etc.
  • Amount of matter per unit volume
• The "dmv" Triangle for Volume, Mass, and Density

  • Density = m/v
  • Volume = m/d
  • Mass = d x v
• A kilogram of feathers takes up more space than a kilogram of steel
• Density


  • How close the atoms or molecules are to each other
  • More than "heaviness" - includes how much space an object takes up
  • All substances have density including liquids, solids, and gases
  • Measure of the "compactness" of a material
• Gases


  • The greater the kinetic energy of the molecules, the greater the volume, and the less dense the gas is
  • Cold air is more dense than warm air
• Low pressure weather system


  Warmer air tends to rise
• High pressure systems


  Colder more dense air mass that will sink
• Liquids


  • The more dissolved solids in a solution, the more dense (such as ocean water)
  • Cold water in lakes tends to sink (this creates a constant mixing of water, nutrients, and other substances)
• Mercury density = 13600kg/m3, Lead density = 11340kg/m3, Lead floats on liquid mercury
• Solids


  • Ice is less dense than water (which is why lakes and ponds have a thin layer of ice covering in winter, with water underneath)
  • Various rocks, woods, metals have a characteristic density specific to that substance
• Archimedes and the Kings Crown
• Factors Affecting Density


  • Temperature
  • Pressure
  • Dissolved solids - in liquids
  • Concentration and kind of substances
• Determining Density


  1. Regular Shapes - mass, then determine the volume by formula

  2. Irregular shapes - mass, then measure displacement of a liquid (usually water) by that irregularly shaped object
• Density Table
• Sink or Float in Water (D = 1.0 g/mL)
• Density equation


  Density = mass / volume

  d = m/v
• Calculating density


  d = m/v

  m = d x v

  v = m/d
• Sample Problems


  • Density of a block of steel

  2. Mass of a block of gold

  3. Volume of a block of ice
• Volume of a liquid

  Measuring cylinder - read off the level on the scale to get the volume of liquid
• Volume of a regular solid

  Length x Width x Height

  π x radius2 x height
• Volume of an irregular solid

  Volume after - volume before

  Using a Eureka (displacement) can
• Density = mass / volume