Damping Forces

All phenomena observed in nature are driven by some kind of stimulus. From the movement of a car, to the rotation of planets, all observed motion is a direct result of the application of force. Without applying force, it would be impossible to do any kind of desired work. But force is not just used to bring about motion but also to slow down motion.

Damping forces are such kinds of forces that are applied to slow down or alleviate motion. A damping force is existent in almost every system that exists in nature or in experiment. Understanding the effect of damping forces is important to understanding the motion of entities as well as predicting the longevity of an experiment, or in other words, how long it will continue without external support.

What are damping forces?

As described earlier, damping forces are a special type of force that are used to slow down or stop a motion. The key point is that damping forces only work on vibratory motion or on systems that exhibit an oscillatory nature. It is a force that restricts the vibrations that can be of mechanical nature or electrical nature. The damping effect caused by damping forces is due to the dissipation of energy.

The aim of any damping force in an oscillatory system is to decrease the frequency of its oscillation or prevent the oscillation from happening. Damping is an effect that is caused by damping forces and occurs in almost every system. For damping to not occur in a system it has to be free of any forces that oppose the oscillatory motion of the force. Such a system is possible in classical mechanics. Every force that is applied receives a response and this response acts as the damping force.

Levels of Damping

There are different levels of damping that can happen on a system;

Undamped

An oscillatory system that oscillates in such a manner that no energy is lost in any oscillation that takes place is called an undamped system, since there is no damping force acting on the system. Such a system will keep oscillating for an infinite amount of time without ever stopping.

Underdamped

A perfectly undamped oscillatory system is not possible. There is always a damping force acting on an oscillatory system. When this damping force is such that the oscillations gradually tend towards zero oscillation, then the oscillatory system is said to be underdamped. In an underdamped system, the oscillating body may pass its starting position more than one time but with every oscillation it loses energy and then eventually stops oscillating.

Critically damped

In many situations it is required that as soon as the body is put into oscillation, the body be brought to rest. For example, when a bike passes over a speed bump, the suspension begins oscillating but stops after a momentary time. In order to achieve a damping such that the oscillation of a body is stopped as soon as it starts oscillating the system has to be critically damped. In the example of the bike, the suspensions are critically damped either mechanically or by adding a viscous liquid that prevents the suspensions from oscillating for too long.

Overdamped

If you swing a door with proper damping very hard, you will notice that the door closes smoothly without swinging back. When an oscillatory system is damped in a manner such that the oscillating body never crosses the starting point of its oscillation, then that system is said to be overdamped. In an overdamped system, the oscillations continue for a period of time but the amplitude of the oscillation is always less than the initial amplitude. The difference between overdamping and critical damping is that critical damping focuses on not allowing oscillations to happen at all but overdamping focuses on the amplitude of the oscillation to sharply decrease. 

Damping Forces Examples

There are different types of damping forces that can occur in a system, the most observed ones are;

Mechanical Damping Forces

For an alternating current system, the oscillations are happening with respect to the polarity of the current being passed. These oscillations of the current are opposed by the damping force provided by resistors. They dissipate the energy carried by the electric current in the form of heat, thus reducing the actual energy received by the receiver.

Viscous Damping Forces

In many oscillating systems, like bike suspensions, the damping effect is induced with the help of a very viscous liquid. In a viscous liquid, viscous drag is observed which is identical in action to friction. When an oscillating body is subjected to viscous drag, the kinetic energy of the body is dissipated at a much faster rate than if the oscillating body was placed in air. Viscous drag often causes the oscillating system to be overdamped which results in the oscillations quickly dying down to zero.

Electrical Damping Forces

For an alternating current system, the oscillations are happening with respect to the polarity of the current being passed. These oscillations of the current are opposed by the damping force provided by resistors. They dissipate the energy carried by the electric current in the form of heat, thus reducing the actual energy received by the receiver.

Electromagnetic Damping Forces

Radiation damping is observed due to electromagnetic damping forces, and is usually observed in subatomic particles. For example, when an electron is excited it starts oscillating, when this oscillation starts, the mechanical energy of the electron is dissipated in the form of electromagnetic waves.

Conclusion

Damping forces are a special type of force that are used to slow down or stop a motion. The key point is that damping forces only work on vibratory motion or on systems that exhibit an oscillatory nature. It is a force that restricts the vibrations that can be of mechanical nature or electrical nature. The damping effect caused by damping forces is due to the dissipation of energy.

An oscillatory system can be undamped, underdamped, critically damped or overdamped. The most observed examples of damping forces are mechanical damping force, viscous damping force, electrical damping force and electromagnetic damping force.A