Physics/Chemistry Yr10 mock

• Pressure in gases

  Particles in a gas are in constant motion, moving quickly and randomly in all directions
• Pressure in gases

  1. Gas placed in sealed container

  2. Particles collide with walls of container

  3. Causes pressure
• Low pressure

  • Fewer particles
  • Fewer collisions
  • Not as much force towards side of container
  • Overall lower pressure
• High pressure

  • More particles
  • More collisions
  • More force towards side of container
  • Overall higher pressure
• Gas is heated

  • Particles have more energy
  • Move faster
  • Increases number of collisions with container
  • More force applied
  • Increases pressure
• Low temperature

  • Particles have less kinetic energy
  • Fewer collisions
  • Slower
  • Less force, less pressure
• High temperature

  • Particles have more kinetic energy
  • More collisions with sides
  • Move faster
  • More force, more pressure
• Temperature is proportional to kinetic energy
• Density


  • Measure of how much mass (particles) there is in a particular volume (space)
  • The more particles in a particular volume, the higher the density
• Solid


  • High density
  • Lots of particles in a small volume
• Liquid


  • Slightly lower density as particles are more spread out
• Gas


  • Low density
  • Small amount of particles in a low volume
• Density calculation


  Density (kg/m³) = mass (kg) / Volume (m³)
• Particle model


  • All materials are made from particles (atoms or molecules)
  • Arrangement of particles determines whether a substance is a solid, liquid or gas
• Solid


  • Particles vibrate slowly
  • Fixed positions
  • Need neat lattice
  • Low energy
• Liquid


  • Particles vibrate faster
  • Touching
  • Can flow
  • Disorganised lattice structure
  • Higher energy
• Gas


  • Particles vibrating faster
  • Move around/move anywhere
  • No neat lattice structure
  • High energy
• Limitations (problems) with the particle model
• Specific latent heat


  • Energy needed to cause a change of state, different for different substances
  • Energy required to make one kilogram of a substance change its state without a temperature change
• Specific latent heat calculation examples

  • 15kg of substance with 30500 J/kg SLH requires 457500J

  1. 25kg of substance with 2800 J/kg SLH requires 210,000J
  2. 22kg of substance requires 16500J to melt, SLH = 750J/kg
  3. 800g of substance requires 0.04kJ to evaporate, SLH = 50J/kg
• Evaporation vs boiling

  Boiling - liquid completely changes to gas at boiling point

  Evaporation - some particles turn to gas below boiling point
• How evaporation occurs


  Evaporation occurs at surface of liquid

  Particles with most energy leave liquid, decreasing average energy and cooling the liquid
• Energy transfers


  Energy can be transferred to or from a store
• Types of energy transfers


  • Mechanical energy transfers
  • Electrical energy transfer
  • Heating energy transfer
  • Waves (e.g. light, sound)
• Dissipation of energy


  Energy transfers can be useful or not useful. Whenever energy is transferred, some of the energy is dissipated (lost)
• Energy cannot be created or destroyed. This means that in a closed system, the total energy remains the same, even though it may be stored in different ways. This is called conservation of energy.
• Joules (J)


  The unit used to measure energy stored or transferred
• Energy transfer examples


  • Torch
  • Washing Machine
  • Hairdryer
• Efficiency


  A measure of how much of the energy transferred is useful, calculated as useful energy out / total energy in
• Calculating efficiency


  1. Useful energy out / total energy in

  2. Multiply by 100 to get percentage
• Reducing unwanted energy transfers

  • Using insulation to reduce heat loss
  • Using lubrication to reduce friction
• Kinetic energy


  The energy of motion, calculated as 0.5 x mass x velocity^2
• Elastic potential energy


  The energy stored in an object that has been squashed or stretched, calculated as spring constant x extension^2
• Kinetic energy store


  Depends on the mass of the object and the speed it is travelling at
• Increasing the speed


  Increases the kinetic energy store of the object
• Increasing the mass


  Increases the kinetic energy store of the object
• Example 1: Car


  • Mass = 1600kg, Speed = 10 m/s, Kinetic Energy = 800,000 J
• Example 2: Bus


  • Mass = 5040kg, Speed = 13.9 m/s, Kinetic Energy = 486,889.2 J
• Elastic potential energy


  Calculated using the equation: Elastic Potential Energy = 0.5 x Spring Constant x Extension^2
• Example 1: Spring


  • Spring Constant = 15 N/m, Extension = 0.5m, Elastic Potential Energy = 1.875 J