Matter & Thermal Physics

• States of matter


  • Solid
  • Liquid
  • Gas
• Solid


  • Does not flow
  • Cannot be squashed
  • Particles in fixed, often regular arrangement
  • Closely packed particles
• Liquid


  • Can flow
  • Cannot be squashed
  • Random arrangement of particles able to move past each other
  • Closely packed particles (slightly further apart than in solid)
• Gas


  • Can flow
  • Can be squashed
  • Random arrangement of rapidly moving particles
  • Widely spaced particles
• Density formula


  • Density = mass / volume or ρ = m/V
  • Units: density in kg/m3, mass in kg, volume in m3 OR density in g/cm3, mass in g, volume in cm3
• Gases are less dense than solids because the molecules are further apart
• Finding density of a regularly shaped solid


  1. Measure mass using mass balance

  2. Measure dimensions using metre rule

  3. Calculate volume from dimensions
• Finding density of a liquid


  1. Measure volume using measuring cylinder

  2. Measure mass of empty beaker using mass balance

  3. Measure total mass of beaker and liquid

  4. Calculate mass of liquid by subtracting mass of beaker
• Finding density of an irregularly-shaped solid

  1. Fully submerge object in liquid in measuring cylinder

  2. Take readings of volume of water and volume of water plus solid

  3. Calculate volume of solid by subtracting volume of water

  4. Alternatively use Eureka can and collect overflowing water in measuring cylinder
• Temperature


  Measure of average kinetic energy of molecules
• Rise in temperature of a body comes from increase in its internal energy (total energy of all its molecules)
• If we could reach absolute zero, all particles would stop moving (impossible)
• Absolute zero


  0 Kelvin or -273 °C
• Heat energy always flows from hot object to cold object (high to low temperature)
• When a solid, liquid or gas gets hotter it tends to expand and the molecules get further apart
• Changes of state


  • Melting
  • Freezing
  • Evaporation
  • Boiling
  • Condensation
  • Sublimation
• Physical changes of state conserve mass and the material recovers its original properties when the change is reversed
• Heating a system


  Causes either an increase in temperature (and internal energy) or a change in state
• Heat capacity


  Amount of energy required to increase an object's temperature by 1°C
• Specific heat capacity


  Energy required to raise the temperature of 1 kg of a material by 1°C
• Melting


  Changing from solid to liquid, requires energy input even though temperature does not change

  
• Specific latent heat of fusion


  Energy input required to melt 1 kg of a substance, to break intermolecular bonds
• Vaporisation


  Changing from liquid to gas, requires energy to overcome intermolecular forces of attraction
• Specific latent heat of vaporisation

  Energy input required to vaporise 1 kg of a substance
• Condensation


  Changing from gas to liquid, energy given out to surroundings as bonds form
• Freezing/Solidification


  Changing from liquid to solid, energy given out to surroundings as bonds form
• Pressure of a gas arises from collisions of particles with walls, creating a force
• Increasing temperature of a gas


  Increases its pressure, as molecules move faster and hit walls with more force
• Work done on a gas increases its temperature, e.g. using a bicycle pump
• If temperature of gas is constant but volume changes, pressure x volume is constant (Boyle's Law)
• Pressure in gases or liquids leads to a force at right angles to the wall of the container
• Increasing depth of liquid or using a more dense liquid increases pressure, but pressure does not depend on area of liquid
• Total pressure in a liquid is atmospheric pressure plus pressure due to depth
• Atmospheric pressure decreases with height
• Upthrust/Buoyancy


  Upwards force on an object immersed in a fluid, due to pressure increasing with depth
• Archimedes' Principle: upthrust = weight of fluid displaced
• An object floats if its density is less than the density of the liquid
• For a floating object, upthrust equals weight of object
• Heating part of a liquid causes it to expand, become less dense, and rise, setting up convection currents
• Elastic distortion


  Spring returns to original length when force removed