Preventing Unwanted Energy Transfers (AQA GCSE Combined Science: Synergy: Physical Sciences): Revision Note

Preventing unwanted energy transfers

• Unwanted energy transfers can be reduced in a number of ways

• The two main methods are:

  • Lubrication

  • Thermal insulation

Lubrication

• Friction is a major cause of wasted energy in machines

• When an object moves against a surface, work is done against the frictional forces acting on it

• This causes a rise in the temperature of the object and dissipates useful energy to the surroundings

• For example, the gears on a bike can become hot if the rider has been cycling for a long time

  • Energy is transferred from the kinetic store of the gears and chain to the thermal store of the gears, chain and surrounding air

  • Lubrication reduces friction between surfaces that rub together, reducing the amount of useful energy that is wasted

Thermal insulation

• In many situations, energy transferred by heating is wanted

  • For example, when heating a home or boiling a kettle

• If this energy can be prevented from dissipating, less energy is needed to maintain the desired temperature

• This can be achieved by surrounding the object or building with insulation

• The effectiveness of insulation depends on two factors:

  • Thermal conductivity

    • The higher the thermal conductivity of a material, the higher the rate of energy transfer by conduction through it

    • Insulation materials should have low thermal conductivity

  • Thickness

    • Thicker insulation reduces the rate of energy transfer

Effect on buildings

• The rate at which a building loses energy (rate of cooling) depends on the thickness and thermal conductivity of its walls

• Thicker walls reduce the rate of cooling

  • So, energy takes longer to conduct through a greater depth of material

• Walls made from materials with lower thermal conductivity also reduce the rate of cooling, as less energy is transferred by conduction per second