What is mechanical energy?

We explain what mechanical energy is and how this energy can be classified. In addition, examples and potential and kinetic mechanical energy.

  1. What is mechanical energy?

We understand by mechanical energy that which a body or a system obtains as a result of the speed of its movement or its specific position, and which is capable of producing mechanical work. In general, mechanical energy  involves both kinetic energy, elastic energy and the potential energy of an object.

Mechanical energy is conserved in conservative fields and in which they form particles of purely mechanical action, thus remaining constant over time , according to the following formulation:

Emec = Ec + Ep + Ee = cte.

Where Ec is the kinetic energy of the system, Ep its gravitational potential energy and Ee its elastic potential energy.

This does not happen in systems of particles charged with movement (since mechanical energy is transformed into electromagnetic), or in thermodynamic systems that undergo state changes (convert it into thermal energy) or in the mechanics of dissipative continuous media (in which energy dissipates due to deformations and heat generation).

Mechanical energy is frequently used to carry out specific work or convert it into other forms of energy, such as hydraulic energy , which takes advantage of the potential energy of the falling water; wind energy, which takes advantage of the kinetic energy of the wind, or tidal energy , which takes advantage of the kinetic energy of the tides.

  1. Types of mechanical energy

Mechanical energy
Kinetic energy has to do with the speed and displacement of objects.

There are two types of mechanical energy, as seen. These are:

  • Kinetic energy . That which is derived from the movement of objects or systems, and that has to do with its speed and its displacement . For example, a moving ball.
  • Potential energy  . That which has to do with the position or shape of objects or systems, on which a work capacity depends, and which in turn can be of two types:
    • Gravitational potential energy . That which is due to the action of gravity on bodies, as is the case with an object that falls from a height.
    • Elastic potential energy . It has to do with the constitution and shape of the material of the object, which tends to recover its original form after having been subjected to forces that deform it, as is the case of a metal spring .
  1. Examples of mechanical energy

Some possible examples of mechanical energy in its different forms are the following:

  • A roller coaster cart . At its highest point of ascent, the cart will have accumulated enough gravitational potential energy (due to the height) to fall freely a second later and convert it all into kinetic energy (due to movement) and reach vertigo speeds.
  • A windmill . The kinetic energy of the wind gives a thrust that the blades of the mill catch and turn into mechanical work: spin the gear that will grind, lower, the grains or the farmer’s wheat.
  • A pendulum . The classic example of how the gravitational potential energy of weight is converted into kinetic energy to make it move along its path, conserving total mechanical energy.
  • A trampoline . The swimmer who jumps on a diving board uses his weight (gravitational potential) to deform the trampoline down (elastic potential) and he, when recovering his shape, pushes him up increasing his height (more gravitational potential) than immediately afterwards converts into kinetic energy during the free fall into the water.
  1. Kinetic and potential mechanical energy

As already said, mechanical energy can be divided into two forms: kinetics (movement) and potential (form or position) .

The first is calculable using the simple formula of Ec = ½ m. v2 and its unit of measurement in the International System will be the Joules (J).

Instead, the potential energy is about the amount of energy stored in the system, due to its particular configuration or its positioning with respect to a gravitational or electromagnetic field, as the case may be. This energy is capable of becoming other forms of energy, such as kinetics itself.

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