Mean Kinetic Energy (SQA National 5 Physics): Revision Note

Mean kinetic energy

• Heat and temperature are related quantities, but they are not the same

• Heat is a measure of the total energy stored in a substance or object

• Temperature is a measure of how hot or cold a substance or object is

Heat

• The total energy of all the particles within a substance or object

• Measured in joules (J)

• Depends on the mass, material and temperature of a substance

Temperature

• The mean (average) kinetic energy of the particles within a substance or object

• Measured in degrees Celsius (°C) or kelvin (K)

• Depends only on particle speed

Heating a substance

• Heating a substance increases the kinetic energy of its particles

• Therefore, the mean kinetic energy of the particles increases, and so the temperature increases

• This also means that the total energy stored within the substance increases, so the heat energy increases

• Two substances can have the same temperature but different amounts of heat energy

• A mug of coffee at 80 °C has less heat energy than a pan of water at 80 °C

• This is because the water in the pan has a greater mass than the coffee in the cup

  • There are a greater number of particles in the pan than in the mug

  • Therefore, the total energy of all the particles is greater in the pan than the mug

  • Even though the speed of particles, and therefore the temperature of the substances, is the same