Energy, Work and Power. Physical definitions.

Date: 13/12/2023 Author: Antonio H.

Energy, Work and Power, some physical definitions

Energy: Energy is the capacity of a system to produce work. A system that has a certain energy will not do any work until that capacity is converted into motion. For example, an apple on a tree has a potential energy, but it does not do any work until it falls.

Its unit in the international system is the Joule (joule) which is the work done by a force of one newton whose point of application is displaced by one meter in the same direction.

Work: Work consists of a transfer of energy between systems. In the case of a force acting on a body, its work is equivalent to the energy required to move it. A force acting on a body is then said to do work when it causes a displacement of the body in the direction of the force. Therefore, in a mechanical system, if there is no displacement, the work is zero. This conclusion is not valid for thermodynamic systems, where heat transfers are considered as energy transfers.
Trabajo de una fuerza
Only the component of the force acting in the direction of displacement is considered to do work, in the case of the figure above it would be the horizontal component of the force F.

Work has the same units as energy.

Power: we can define power as the amount of work or energy use we perform in a given time. It is the speed at which we perform work or use energy.

Units: watts.

One watt of power is generated when work is done that consumes 1 Joule of energy during 1 second of time.. 1 w = 1 joule/ 1 segundo

 
Power formula

Graphically, energy is the area under the graph of power as a function of time:

Grafica potencia y energía
In the figure above, where the curve of the power developed over time is shown, the area colored in yellow corresponds to the energy consumed between instants t1 and t2.
 

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