Mechanical energy


Mechanical energy is that which a body or system derives from the speed of its movement or its specific position and which is capable of producing mechanical work. It is produced by mechanical forces, such as elasticity, gravitation, etc., and bodies have it in motion or displaced from its equilibrium position.

In general, mechanical energy involves both kinetic energy, elastic energy, and potential energy of an object.

Mechanical energy is often used to do specific work or to convert it into other forms of energy, such as hydraulic energy, which harnesses the potential energy of falling water; wind energy, which uses the kinetic energy of the wind, or tidal energy, which uses the kinetic energy of the tides.

This does not occur in systems charged with movement (since mechanical energy is transformed into electromagnetic particles), nor in thermodynamic systems that go through changes of state (transforming into thermal energy) nor in dissipation mechanisms of continuous media (in which the energy dissipates due to deformation and heat generation).

Mechanical energy formula

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

Emec = Ec + Ep + Ee = cte.


Ec: is the kinetic energy of the system

Ep: its gravitational potential energy

Ee: its elastic potential energy.

Types of mechanical energy

There are two types of mechanical energy:

Kinetic energy:

That which is derived from the movement of objects or systems, and which has to do with their speed and displacement. For example, a ball in motion.

Energy potential:

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 of an object falling from a height.

  • Elastic potential energy:

It has to do with the constitution and shape of the object’s material, which tends to regain its original shape after being subjected to forces that deform it, such as a metal spring.

Examples of mechanical energy

Mechanical energy according to its different forms can be exemplified as follows:

A pendulum:

The classic example of how the potential gravitational energy of the weight is converted into kinetic energy to make it move on its way, preserving the total mechanical energy.

A roller coaster cart:

At its highest point of ascent, the car will have accumulated enough gravitational potential energy (due to height) to freely fall a second later and convert it all to kinetic energy (due to motion) and reach blazing speeds.

A springboard:

The swimmer who jumps on a springboard uses his weight (gravitational potential) to deform the springboard downwards (elastic potential) and the latter to regain its shape, pushes it upwards to increase its height (gravitational potential) which is converted into kinetic energy during free fall into the water.

A windmill:

The kinetic energy of the wind gives an impulse that the blades of the mill endure and become mechanical work: turning the gear that will crush, underneath, the farmer’s grain or wheat.

Forms of mechanical energy

Energy can manifest itself in different ways: in the form of movement (kinetic), position (potential), heat, electricity, electromagnetic radiation, etc … Depending on the process, it is called energy:

  1. Thermal energy
  2. Electricity
  3. Radiant energy
  4. Chemical energy
  5. Nuclear energy

Principle of Conservation of Mechanical Energy

The mechanical energy of a body remains constant when all the forces that work in it are conservative, the principle is: “energy is neither created nor destroyed, it only transforms.”

Mechanical energy example

Imagine a ball hanging from the ceiling that falls onto a pier. According to the principle of conservation of mechanical energy, the mechanical energy of the ball is always the same and, therefore, the entire process in which the energy remains constant will only change the contributions of the different types of energy that make up the energy. mechanics.

Before falling, the mechanical energy of the ball is formed only by the potential gravitational energy. As you fall and gain speed, the gravitational potential energy is converted into kinetic energy, leaving the mechanical energy constant. Finally, when it reaches the spring, it begins to compress, causing the mechanical energy to be made up of kinetic energy, energy of gravitational potential, and energy of elastic potential.

Therefore, the mechanical energy does not change, it remains constant.

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