Work, energy and power are closely related concepts in physics. Work is done when a force moves an object, energy is the capacity to do work, and power is the rate of doing work. These terms with their units are common in general science papers.
Work
- Work = Force x Displacement (in the direction of force).
- SI unit of work is the joule (J).
- If there is no displacement, work done is zero.
- Example: pushing a wall that does not move means zero work.
Energy
- Energy is the capacity to do work; its SI unit is also the joule.
- Kinetic energy is energy due to motion (KE = 1/2 mv squared).
- Potential energy is energy due to position (PE = mgh).
- Other forms: heat, light, sound, chemical, nuclear energy.
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Law of Conservation of Energy
- Energy can neither be created nor destroyed.
- It only changes from one form to another.
- Example: in a falling body, potential energy converts to kinetic energy.
Power
- Power = Work / Time; it is the rate of doing work.
- SI unit of power is the watt (W).
- 1 horsepower (hp) = 746 watts.
- 1 kilowatt-hour (kWh) is the commercial unit of electrical energy.
Quick Revision Points
- Work = Force x Displacement; unit is joule.
- No displacement means zero work.
- KE = 1/2 mv squared; PE = mgh.
- Energy is conserved, not created or destroyed.
- Power = Work / Time; unit is watt.
- 1 hp = 746 watts.
- Commercial unit of electricity is kWh.