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Power in mechanical systems is the combination of forces and movement. In particular, power is the product of a force on an object and the object's velocity, or the product of a torque on a shaft and the shaft's angular velocity. Mechanical power is also described as the time derivative of work.
This also means the constraint forces do not add to the instantaneous power.) The time integral of this scalar equation yields work from the instantaneous power, and kinetic energy from the scalar product of acceleration with velocity. The fact that the work–energy principle eliminates the constraint forces underlies Lagrangian mechanics. [28]
Mass times acceleration due to gravity times height divided by the time it takes to lift the object to the given height gives the rate of doing work or power. [i] A laborer over the course of an eight-hour day can sustain an average output of about 75 watts; higher power levels can be achieved for short intervals and by athletes. [4]
The concepts invoked in Newton's laws of motion — mass, velocity, momentum, force — have predecessors in earlier work, and the content of Newtonian physics was further developed after Newton's time. Newton combined knowledge of celestial motions with the study of events on Earth and showed that one theory of mechanics could encompass both.
Power is the work per unit time, given by =, where P is power, τ is torque, ω is the angular velocity, and represents the scalar product. Algebraically, the equation may be rearranged to compute torque for a given angular speed and power output.
The work can be done, for example, by electrochemical devices (electrochemical cells) or different metals junctions [clarification needed] generating an electromotive force. Electric field work is formally equivalent to work by other force fields in physics, [1] and the formalism for electrical work is identical to that of mechanical work.
Electric power is the rate of transfer of electrical energy within a circuit.Its SI unit is the watt, the general unit of power, defined as one joule per second.Standard prefixes apply to watts as with other SI units: thousands, millions and billions of watts are called kilowatts, megawatts and gigawatts respectively.
In physics, there are equations in every field to relate physical quantities to each other and perform calculations. Entire handbooks of equations can only summarize most of the full subject, else are highly specialized within a certain field. Physics is derived of formulae only.