P6 : molecules and matter

• Density

  The mass of an object divided by its volume
• Density of different materials

  • Feathers
  • Gold
• Calculating density of a regular shape (cube)

  1. Measure length, width, height

  2. Calculate volume (length x width x height)

  3. Divide mass by volume
• Units for density


  Kilograms per meters cubed
• Calculating density of an irregular shape

  1. Use Archimedes' principle

  2. Measure volume of water displaced

  3. Subtract initial water volume from final volume to get object volume

  4. Divide mass by volume
• States of matter

  • Solid: particles in fixed positions, can only vibrate
  • Liquid: particles can slide past each other, not in fixed positions
  • Gas: particles have high energy, move randomly, not touching
• Heating/cooling curve


  • Flat parts show change of state
  • Latent heat: energy required to change state
• Latent heat of fusion


  Energy required to change from solid to liquid
• Latent heat of vaporization


  Energy required to change from liquid to gas
• Measuring latent heat

  1. Use heater and Joule meter

  2. Measure mass change

  3. Energy = mass x latent heat
• Internal energy

  Kinetic energy + potential energy of particles
• Gas pressure

  • Caused by random motion and collisions of gas particles
  • Increases with temperature, number of particles, or decreased volume
• Calculating gas pressure and volume (Boyle's law)


  P1V1 = P2V2
• Pressure is measured in Pascals (N/m^2)