3.4.1.7
Energy cannot be created or destroyed, only transferred between forms
Work, Energy & Power — AQA A-Level Physics
Key Definition
Conservation of energy — Energy cannot be created or destroyed. It can only be transferred from one form to another. The total energy in a closed system remains constant.
- Common energyThe capacity to do work. Measured in joules (J). forms: kinetic, gravitational potentialThe work doneEnergy transferred when a force moves an object. In electrical circuits, W = QV (chargeA property of matter that causes it to experience a force in an electromagnetic field. Measured in coulombs (C). times potential difference). per unit mass in bringing a small test mass from infinity to that point. Always negative. Measured in J kg⁻¹., elastic potential, chemical, nuclear, internal (thermal).
- Falling object (no air resistanceThe opposition to currentThe rate of flow of chargeA property of matter that causes it to experience a force in an electromagnetic field. Measured in coulombs (C).. Measured in amperes (A). flow. The ratio of potential difference to currentThe rate of flow of chargeA property of matter that causes it to experience a force in an electromagnetic field. Measured in coulombs (C).. Measured in amperes (A).. Measured in ohms (Ω).): GPE converts to KE.
- Mass on a spring: elastic PE converts to KE and back.
- Object on a rough slope: loss in $KE = gain$ in GPE + work doneEnergy transferred when a force moves an object. In electrical circuits, W = QV (charge times potential difference). against friction.
- Dissipated energyThe capacity to do work. Measured in joules (J). (heat, sound) is wasted but still conserved in total.