Power and energy; definitions and reminders

Power / Energy

In physics, power is the quantity of energy per unit of time supplied by the studied system to another system; therefore, the power corresponds to the time variation of energy. Two systems of different power can deliver the same energy, but the more powerful system will deliver this energy faster, in a smaller time interval.

Power is always equal to the product of an effort quantity (force, torque, pressure, tension, etc.) by a flux quantity (linear velocity, angular velocity, flow, current intensity, etc).

Instantaneous power/ mean power

The mean power Pm characterizing a process is the ratio between the supplied energy or delivered energy W during the process duration T and this duration, respectively: Pm = W/T

The instantaneous power P(t) is the derivative of time variation of the supplied or delivered energy W(t) with respect to time, respectively: P(t)=dW/dt