mechanical energy



We explain what mechanical energy is and how it can be classified. Also, examples and potential and kinetic mechanical energy.

Mechanical energy involves both the kinetic, elastic, and potential energy of an object.

What is mechanical energy?

Mechanical energy is the sum of the kinetic energy and the potential energy of a body or system. Kinetic energy is the energy that bodies have in movement, since it depends on their speeds and their masses. Potential energy, on the other hand, is associated with the work of forces that are called conservatives, such as the elastic and gravitational forces, which depend on the mass of the bodies and their position and structure.

The Principle of conservation of energy establishes that mechanical energy is conserved (remains constant) as long as the forces acting on the body or system are conservative, that is, they do not make the system lose energy. This principle can be written mathematically as follows:

Emec = Ec + Ep = cte

whereEc is theKinetic energy of the system andEp hispotential energy, which can be gravitational, elastic, electric, etc.

This relationship does not hold if the system is affected by non-conservative forces. For example, in the case of movements on surfaces with friction (like most surfaces), the kinetic energy dissipates in the form of heat. The mechanical energy of a system can also be lost in the form of heat, for example in thermodynamic systems in which mechanical energy can be converted into thermal.

Mechanical energy is frequently used to carry out work or convert it into other forms of energy, such as thehydraulic energy (when man takes advantage of the potential energy of falling water to do work). Another example is wind power orSeawater energy, which uses the kinetic energy of the wind and tides to transform them into another type of useful energy.

Types of mechanical energy

Kinetic energy is related to speed and displacement of objects.

Mechanical energy is the sum of the following energies:

  • Kinetic energy. It is the energy possessed by objects or a moving system, and which depends on their speed and their mass. For example: a ball in motion.
  • Potential energy. It is the energy associated with the position of a body within a conservative force field, such as gravitational, elastic, electrical, etc. In turn, potential energy can be two types:
    • Gravitational potential energy. It is the energy that is due to the action of thegravity over the bodies. For example: an object that falls from a certain height.
    • Elastic potential energy. It is the energy possessed by systems deformed by a force. The energy remains in the system until the force is no longer applied and thus the system returns to its original shape, transforming the elastic energy into kinetic energy. For example: a spring that is stretched or contracted by means of an external force that, when it is not applied, allows the spring to return to its normal position, of equilibrium.

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, the cart will have accumulated enough gravitational potential energy (due to height) to freely fall one second later and convert it all to kinetic energy (due to motion) and reach blazing speeds.
  • A windmill. The kinetic energy of the wind provides a push to the blades of the mill that turns into mechanical work: turning the gear that will grind the grains lower.
  • A pendulum The gravitational potential energy of theweight it is converted into kinetic energy to make it move along its path, conserving the total mechanical energy.
  • A springboard. The bather who jumps from a diving board uses his weight (gravitational potential energy) to deform the diving board downwards (elastic potential energy) and this, when it regains its shape, pushes it upwards increasing its height (more gravitational potential) which act it is often converted to kinetic energy during free fall into the water.

Kinetic and potential mechanical energy

As has already been said, mechanical energy involves two energies: kinetic and potential.

The first is calculable by the simple formula ofEc = ½ m. v2 and your unit of measurement at International system will be the Joules (J).

Instead, potential energy is the amount of energy stored in the system due to its particular configuration or its positioning with respect to a field of forces (gravitational, elastic or electromagnetic). This energy is capable of being converted into other forms of energy, such as kinetics itself.

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