Unit 1.3

• Density


  Calculated using the equation: density = mass / volume
• You do not have to remember the density equation, but it is important to choose the correct values to use
• Units of density


  g/cm3 or kg/m3
• Calculating the density of a regularly shaped solid

  1. Measure mass using a balance

  2. Measure length, width and height using a ruler

  3. Calculate volume using: volume = length x width x height

  4. Calculate density using: density = mass / volume
• Calculating the density of an irregularly shaped solid

  1. Measure mass using a balance

  2. Fill a measuring cylinder with water to a specific volume

  3. Place the solid in the measuring cylinder and record the new volume

  4. Calculate the volume of the solid by subtracting the initial volume from the new volume

  5. Calculate density using: density = mass / volume
• Calculating the density of a liquid

  1. Measure mass of an empty measuring cylinder

  2. Fill the measuring cylinder with a specific volume of the liquid and record the volume

  3. Measure the combined mass of the measuring cylinder and the liquid

  4. Calculate the mass of the liquid by subtracting the empty mass from the new mass

  5. Calculate density using: density = mass / volume
• If the solid floats in the water, you must use something to ensure the solid is completely under the water. Remember if you use something to sink the solid you must subtract its volume and the volume of the water from the new volume.
• Work done = force x distance moved in direction of force
• The greater the difference in temperature

  The greater the rate of heat transfer
• A mug of tea at 90˚C

  Cools quicker outside where the temperature is 5˚C than in the house where the temperature is 20˚C

  
• Radiation


  All warm things emit heat radiation in the form of infrared waves
• Hotter bodies


  Emit more radiation than cold bodies
• Radiation can travel through solids, liquids, gases and through a vacuum like space
• Radiation travels in all directions from the hot body into a colder body
• Black surfaces


  Absorb radiation best and emit radiation best
• Tea in a black mug

  Cools down quicker than tea in a white mug
• Shiny surfaces


  Reflect radiation well but are poor emitters and absorbers
• Heat always transfers from hot to cold
• Conduction


  Happens in solids, heat energy causes the particles to vibrate more and is transferred from one particle to the next as they collide
• Metals


  • Are the best conductors as they have free electrons that can move the energy quickly from the hot side to the cold
• Air


  Is a poor conductor as it is a gas, it has large gaps between particles and reduces the rate of collisions, making it very useful as an insulator
• Convection


  Happens in liquids and gases, heat energy causes the particles to move quicker and make them move further apart, this means there will be fewer particles in a specific volume and therefore will be less dense, this less dense liquid or gas will rise above the denser cold liquid, this forms a convection current
• Loft insulation


  • Reduces heat loss due to conduction, fibreglass wool between the ceiling and the loft space has pockets of trapped air which acts as an insulator
• Double glazed windows


  • Reduce heat losses due to conduction, trapping air between two layers of glass acts as an insulator
• Stopping draughts


  • Reduces convection currents in the house through stopping cold air being sucked into the house as the hot air inside rises
• Floor insulation


  • Reduces heat losses due to conduction, fibreglass wool below the floor has pockets of trapped air that acts as an insulator
• Cavity walls


  • Reduce heat losses due to conduction, trapping air between two layers of bricks acts as an insulator, filling the cavity (gap) with fibreglass wool or foam stops the air in the gap moving and reduces convection
• Comparing different methods of insulating the home

  Calculate the payback time, which is the time it takes to save the same amount as the initial cost of insulation
• Convection - Simplified 


  The transfer of heat through liquid and gases, hot liquids and gases will rise whilst cold liquids and gases fall - change in density
• Conduction - Simplified


  The transfer of heat through solids - good conductors of heat tend to be metals, whilst poor conductors are called insulators
• Thermal Radiation - simplified


  How thermal energy moves through space, space is a vacuum that contains virtually no molecules - anything above -273°c will release thermal radiation
• Density in states of matter

  • Solids
  • Liquids
  • Gases
• Solids


  Regular arrangement of atoms all packed closely together. when the atoms move they vibrate around a fixed position
• Liquids


  Random arrangement of atoms which are close together - the atoms move around eachother
• Gases


  Random arrangement of atoms which are far apart - the atoms move quickly in all directions