physics st2 (year 9)

• an object or material with a low rate of heat loss or transfer is a good insulator
• factors which affect heat loss:

  • colour
  • surface area (bigger means there is more heat loss)
  • material
  • surface placed on
• silver surfaces reflect radiation back onto the hot object
• bigger temperature difference = bigger rate of heat transfer
• resolution is the smallest point a measuring device can measure
• how to insulate a house:

  • walls - cavity wall insulation when foam is placed between two walls containing air which is an excellent insulator
  • floor - underlay
  • roof - fibre glass insulation when thick fibres decrease thermal conductivity and traps air
  • windows - double glazing to trap air
  • doors - letterbox with bristles to trap air and insulated frames by steel
• payback time = cost of insulation/energy bill saving
• thermal conductivity is the ability of a substance to transfer and conduct heat
• conduction is when particles collide to pass on energy directly and vibrate more
• Particles colliding to pass on energy

  1. Directly

  2. Tubeste more
• Solids are good conductors


  Particles are close together
• Gases are poor conductors


  Particles are far apart
• Metals are good conductors

  • They contain delocalised electrons
  • As electrons gain energy, they collide with ions (greater heat transfer)
  • They also diffuse quickly
• Convection movement


  Transporting heat to cooler areas
• Thermal radiation

  Emission transfer of heat energy through electromagnetic
• Heat always travels from a hot place to a cold place
• Emission

  Heat taken out
• Absorption

  Heat taken in
• Solids

  • All particles are the same size
  • Tightly packed and touching
  • Regular arrangement
  • Strong forces of attraction
  • High density
  • Little kinetic energy
  • Particles vibrate in fixed position
  • Difficult to compress
  • Fixed shape
  • Fixed volume
• Gases

  • Particles not touching
  • Negligible forces
  • Random arrangement
  • Move quickly in all directions
  • Most kinetic energy
  • Low density
  • Fill container
  • Gas pressure = particles collide with surface
  • Can be compressed
  • Pressure increases as heated
  • Nothing between particles
  • Takes volume of container
• Liquids

  • Not tightly packed
  • Randomly arranged
  • Weaker forces of attraction
  • Particles move around each other
  • Medium density
  • Medium kinetic energy
  • Fill container
  • Can be poured
  • Can be frozen
  • Can be evaporated
  • Can't be compressed
• Density

  The number of particles in a given volume/space
• Measuring density of a regular object

  1. Measure height/width/volume and multiply (for a prism, work out cross-sectional area then multiply by length)

  2. Measure mass using a balance

  3. Divide mass by volume
• Measuring density of an irregular object

  1. Measure mass using a balance

  2. Fill container until spout

  3. Measure volume using a displacement can and measuring cylinder

  4. The volume of water displaced is the volume of the object

  5. Divide mass by volume
• Non-renewable energy

  • Cannot be replenished
  • Fossil fuels made from dead organisms compressed (coal, oil, gas)
  • Nuclear - does not release CO2/SO2, produces dangerous nuclear waste, takes days to start off, efficient (lots of energy per kg)
  • Fossil fuels are convenient, fairly plentiful, add to global warming (CO2 and SO2 released, incomplete combustion => particulates block sunlight), environmental damage
• Renewable energy

  • Can be replenished
  • Don't contribute to global warming
  • Most don't release CO2/SO2
  • Biofuels - near zero carbon emission (absorb release)
  • Free resources
  • Allows electricity in remote areas
  • Wind/solar are unreliable, cloud cover affects solar intensity/night time
  • Hydroelectric, tidal, geothermal - expensive, flood areas
• Energy efficiency

  The more efficient an object, the less energy is wasted
• Types of energy

  • Chemical - released during chemical reactions/bonds
  • Kinetic - of moving objects
  • Gravitational potential - raised above surface against gravity
  • Elastic potential - stretched, squashed or compressed
  • Internal - total kinetic and potential in a system
  • Thermal - amount of internal due to temperature
  • Electrostatic - electrostatic forces between charges/charged objects
  • Nuclear - energy stored in nucleus/atomic nuclei
  • Magnetic - in magnetic materials
• Energy conservation

  Energy can't be created or destroyed, only transferred
• Useful energy

  Energy we want
• Wasted energy

  Energy we don't want, dissipates
• Efficiency

  Useful power out / total power in
• Power states the amount of energy transferred in a second
• the higher the thermal conductivity, the faster the conduction
• metals are good conductors because they contain delocalised electrons which gain energy to collide with ions and diffuse quickly
• gases are poor conductors because particles are far apart
• solids are good conductors because particles are close together
• convection is the movement through a substance transporting heat to cooler areas
• thermal radiation is emission or transfer of heat energy through electromagnetic waves
• good absorbers and emitters are black and dull