3.6.2.1
Internal energy is the total random kinetic and potential energy of all particles
Thermal Energy Transfer — AQA A-Level Physics
Key Definition
Internal energy — The sum of the randomly distributed kinetic and potential energies of all the particles in a body. Symbol: U. Unit: joules (J).
- Kinetic energyThe capacity to do work. Measured in joules (J).The energyThe capacity to do work. Measured in joules (J). an object possesses due to its motion. of particles is due to their random motion (speed).
- Potential energyThe capacity to do work. Measured in joules (J). is due to intermolecular forces and varies with particle separation.
- Particles are randomly distributed, meaning they have different speeds and separations.
- Higher temperature means higher average kinetic energyThe energy an object possesses due to its motion..
- Gases have the highest internal energyThe sum of the randomly distributed kinetic and potential energies of all the molecules in a system.; solids have the lowest.
Changing internal energyThe sum of the randomly distributed kinetic and potential energies of all the molecules in a system.
- Internal energyThe sum of the randomly distributed kinetic and potential energies of all the molecules in a system. increases when: work is done on the system, or thermal energy is added (heating).
- Internal energy decreases when: the system does work on its surroundings, or thermal energy is lost to surroundings.
Examiner Tips and Tricks
- When defining internal energy, you must mention 'random' -- either 'random motion' of the particles or 'random distribution' of energies.
- Missing this word loses a mark.