Power (physics)
Power is the rate of energy transfer per unit time.
Power is a fundamental physical quantity defined as the rate at which energy is transferred or converted per unit time. In the International System of Units, its unit is the watt (W), equal to one joule per second. Power is a scalar quantity and is central to understanding mechanical, electrical, and thermal systems.
- SI unit
- watt (W)
- Definition
- rate of energy transfer or conversion per unit time
- Dimension
- energy divided by time
- Common units
- horsepower (hp), ergs per second, foot-pounds per minute, dBm, calories per hour, BTU per hour, tons of refrigeration
- Mechanical power formula
- product of force and velocity, or torque and angular velocity
- Electrical power formula
- product of current and voltage
Lore & Background
Power is defined as the time derivative of work or total mechanical energy: P = dE/dt. For work-only systems, it is also P = dW/dt. The mechanical power generated by a force F on a body moving at velocity v is given by P = F · v. If the force is constant over a distance, work is W = F · x, leading to P = F · v. For variable forces along a curve, work is expressed as a line integral, and the fundamental theorem of calculus yields the same instantaneous power formula.
Reader's Guide
The concept of power distinguishes between energy quantity and energy delivery rate. For example, burning one kilogram of coal releases more energy than detonating a kilogram of TNT, but the TNT reaction delivers more power because it releases energy more quickly. Average power over a time interval Δt is ΔW/Δt, while instantaneous power is the limit as Δt approaches zero. When power is constant, work equals power multiplied by time. In older works, power is sometimes called activity. Understanding power is essential for analyzing engines, electrical circuits, and any system involving energy conversion.
Did You Know?
- The unit of power in the International System of Units is the watt (W), equal to one joule per second.
- The output power of a motor is the product of torque and angular velocity.
- In older works, power is sometimes called activity.
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