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# Damping Torque

We know that torque is an important concept of Physics. Torque is defined as the measure of the force that can cause an object to rotate about an axis. In this session, let us learn in detail about damping torque and the production of damping torque.

## What is Damping Torque?

Damping torque is defined as the physical process of controlling the movement of a system by producing the motion such that it opposes the natural oscillation of the system. An indicating instrument provides the damping torque.

The damping torque and the speed of rotation of the moving system are proportional to each other. This relationship between the damping torque and the speed of rotation is given as:

Tv = kv d dt𝛳

Where,

• kv is the damping torque constant
• d dt𝛳 is the speed of rotation of the moving system

### Conditions Under Damping Torque

The graph is depicts the conditions of an instrument depending on the degree of damping that is introduced in the moving system. There are three possible conditions and they are:

• Under damped condition: This happens when the response is oscillatory.
• Over damped condition: This happens when the response is dragging, and it takes time to rise from zero to the final position.
• Critically damped condition: This happens when the response settles down without any oscillations.

Among the three conditions of damping, the under-damped condition is the best in practice.

## Production of Damping Torque

There are four ways of producing damping torque, and they are:

• Air friction damping
• Fluid friction damping
• Eddy current damping
• Electromagnetic damping

### Air Friction Damping

The air friction damping is created in an air chamber by moving the piston in and out. As the piston enters the chamber, compression is caused inside the chamber. As the piston moves out of the chamber, a force is experienced by it. Air friction damping is the best suitable method of damping torque where the electric field is relatively weak. This is due to the absence of electric components in air damping friction which could deform the electric field.

### Fluid Friction Damping

The fluid friction damping is created due to the oscillation of the disk in and out of the liquid. The liquid that is generally used is oil. The working of the fluid friction damping is similar to that of the air friction damping. The only difference is that instead of air, fluid is used in the chamber.

The fluid friction damping has its own advantages and disadvantages, and they are:

 Advantages: The oil used in the fluid friction damping can also be used as an insulating fluid. Fluid friction is suitable for electrostatic type instruments as these instruments are suspended rather than pivoted. Disadvantages: Since the liquid needs to be in an upright position, this method of damping torque can be used vertically. Keeping instruments clean might be difficult as the leakage of oil cannot be maintained.

### Eddy Current Damping

In eddy current damping, eddy current and electric fields are used for creating an electromagnetic torque that can oppose the motion. The damping torque produced in the eddy current damping is proportional to the strength of the current and the magnetic field. Eddy current damping is considered to be one of the most efficient methods of damping torque. However, the disadvantage of this method is that it may distort the weak electrical fields.

### Electromagnetic Damping

Electromagnetic damping can be achieved by passing the electric current through a magnetic coil such that the torque generated is acting against the natural movement of the coil. The disadvantage of electromagnetic damping is similar to that of eddy current damping. This method of damping torque is commonly used in galvanometers.

See the video below, to understand the work done by torque.

## Frequently Asked Questions – FAQs

### Which damping is most efficient?

Eddy current damping is the most efficient damping.

### Which type of damping is used for providing damping torque in dynamometer type instruments?

Eddy current damping is used for providing damping torque in dynamometer type instruments.

### What type of controlling torque is used in energy meter?

There is no controlling torque used in an energy meter.

### What is a good damping factor?

When the damping factor is between the number range of 50-100, it is said to be a good damping factor.