Energy stores (kinetic, gravitational, elastic, thermal, chemical, nuclear, magnetic, electrostatic), the four energy transfer pathways, the law of conservation of energy, and how energy is dissipated to the surroundings.

A P7 question worth four marks. As the ball falls, energy is transferred from its gravitational potential energy store to its kinetic energy store (1 mark). When it hits the ground and bounces, some energy is transferred to thermal energy stores (of the ball, ground and air) by heating and to the surroundings by sound (1 mark). Energy is conserved overall (the total stays the same), but because some has been dissipated to the surroundings as wasted thermal energy, less energy is left in the ball's stores, so it cannot rise back to the same height (2 marks for conservation plus dissipation explaining the lower bounce). Markers reward the store-to-store transfers, energy dissipated to the surroundings, and conservation explaining the lower bounce. A common error is to say energy is "lost" or destroyed.

A P7 question worth three marks. The law of conservation of energy states that energy cannot be created or destroyed, only transferred from one store to another (or one form to another); the total energy of a closed system stays constant (2 marks for cannot be created or destroyed and total stays the same). Energy is dissipated when it is transferred to the surroundings, usually as thermal energy (heat), spreading out so that it is no longer useful (1 mark). Markers reward the conservation statement and dissipation as energy spreading to the surroundings as wasted heat. A common error is to say dissipated energy is destroyed; it is spread out, not lost.