Nonconservative Forces

Since the beginning of science , what is known as a ” perpetual mobile ” has been sought , a machine or device that remains indefinitely in its state of motion without the need for an external input of energy.

Its discovery would mean the hope of obtaining an inexhaustible source of energy. Unfortunately, today we know that the existence of this type of device is impossible because in the real world there are forces, called dissipative or non-conservative, whose work transforms mechanical energy into other types of more degraded and therefore less useful energies. causing the mechanical energy of the system to decrease and finally be exhausted.

One of the fundamental laws of physics is the law of the conservation of energy, which may have a partial character in the law of the conservation of mechanical energy, in which potential energy, kinetic energy, and work are linked as forms intimately related to the manifestation of the total energy of a system; and universal character in the first law of thermodynamics, which adds heat energy to the energy equation as another way of manifesting the energy of a system. The essence of these laws is that all forms of energy can be transformed from one to another but in such a way that the total energy of the system is always conserved. The key phrase “is conserved” leads to the fact of differentiating the forces into two types, conservative and non-conservative.

PHYSICAL forces that act on a system in order to modify it are called non-conservative/dissipative forces and the forces that do not alter the energy of the system are called conservatives.

We can bodly say thanks to the concept of energy that science has made great advances, in particular, physics, as this concept is present in several branches of this area of ​​knowledge, such as the study of mechanics, thermology, optics and nuclear physics. In part, this is due to the property of physical systems to transform one energy modality into another.

We know that it is possible to transform any type of energy into another, but, literally, it is impossible to spend or create energy. For example, by simply lighting a flashlight or turning on a radio to the battery, we are transforming chemical energy (from batteries) into other forms of energy, such as electrical energy, which is then transformed into light energy and heat, in the case of radio, the energy is transformed into sound energy.

In many cases, we can also pass energy from one body to another. A basic example of this energy transfer is energy from the Sun, it transfers energy to us in the form of light. With this and based on the principle of energy conservation, we see that the total energy of an isolated system is always the same, that is, it is constant.

Conservative Forces

In physics, we define conservative forces as those that do not modify the mechanical energy of the system. It is possible to establish a classification for the different types of forces through the effects caused by each one on the mechanical energy of the bodies. For example, the weight force has the property of transforming the potential gravitational energy into kinetic energy. The force of a spring can transform elastic energy into kinetic energy.

Moreso, the work done by the force of gravity depends only on the initial and final positions, and this amount of work is independent of the path used to move from one point to another.

When a force exhibits this property it is called a conservative force , derived from the fact that the action of the force results in the transformation of one type of energy to another (work to potential energy or vice versa) in a completely reversible process without the total initial energy of the system is reduced by any amount. We can then define a conservative force as:

A force is conservative if the work done on an object moving between two points is independent of the path followed by the object between the two points. The work done by a conservative force on a body depends only on the initial and final positions of the body.

These two types of forces mentioned above, gravitational and elastic forces, are examples of conservative forces, as these forces do not modify the mechanical energy of the system.

Non-Conservative Forces/Dissipative Forces

In physics, we define dissipative forces , which can also be called non-conservative forces, as the forces that transform mechanical energy into other forms of energy, such as sound, heat and deformation.

A good example of a non-conservative force is the frictional force. The frictional force stops an object, transforming its initial kinetic energy into heat and sound. Whenever there is frictional force, part of the mechanical energy of the system will be transformed into heat and sound. It is possible to verify this when a car brakes sharply: we hear the characteristic sound of the braking and see the smoke from the tires burning due to the increase in temperature due to the frictional force with the asphalt.

Moreso,  When a body moves on a real horizontal surface, the work done by the force that performs the movement depends on the path followed by the body between the initial and final points of the movement. Note that a part of the energy applied as mechanical work to the system is “lost” by heating due to friction, so the transformation between work and kinetic energy or potential energy is not complete.

We all take this situation into account intuitively, and therefore no one thinks of dragging a piece of furniture from one place to another in a room making the trip in a zig zag, our preference will always be to move it in a straight line and thus travel the smallest possible distance and therefore make the least effort (equivalent to work).

In a nutshell, a force is non-conservative if the work done on an object moving between two points will depend on the path used.

See Also
Difference between Heat and Temperature