Work and energy
Track how energy is transferred and transformed while total energy remains conserved.
Work in physics#
Mechanical work occurs when a force has a component in the direction of displacement. Holding a heavy object still can be tiring, but no mechanical work is done on the object if it does not move.
Energy forms#
Kinetic energy is associated with motion. Gravitational potential energy depends on height in a gravitational field. Elastic, chemical, thermal, electrical, and radiant energy are other useful forms.
As an object falls, gravitational potential energy decreases while kinetic energy increases. Air resistance transfers some mechanical energy into thermal energy and sound.
Power#
Power measures how quickly work is done or energy is transferred. Two machines may transfer the same energy, while the one completing the task sooner has greater power.
Common mistakes#
Energy conservation does not mean useful energy never becomes dispersed. Real processes often convert concentrated energy into less useful thermal energy.
Track a system#
Choose the system boundary, list energy stores before and after, and identify transfers. This makes conservation statements clear and prevents treating energy as a material substance.
Key points
- Mechanical work transfers energy when a force acts through a displacement.
- Kinetic energy belongs to motion; potential energy depends on position or configuration.
- Power is the rate of energy transfer.
- Energy transforms between forms rather than being created from nothing.