Torque or Couple: Definition, Formula and Examples

In a simple definition, torque is a measurement of force that influences an object to rotate about its axis. Torque, similarly, causes an angular acceleration in the objects. Simply, it can be defined as the rotational equivalent of a linear force. Torque tends to help an object to rotate, by means of two ways. While, couple, as per the physics language, appears when two equal and parallel forces act opposite to one another. To add more, Torque is a vector quantity as well, while the moment of a couple is a free vector.

Types of Torque

Torque can be defined in either of the two ways; static or dynamic. Which is to say, static torque can be described as a torque that does not produce angular acceleration.

For instance, a person who is pedaling a cycle at a rather constant speed can be considered as one of the finest examples of static torque. 

On the other hand, dynamic torque can be witnessed only if it produces a rotation. For instance, a driver accelerating a car from the start line is producing a dynamic torque since it emits an angular acceleration along the track line.

Calculation of Torque

You can evaluate the magnitude of torque by primarily determining which is the lever arm, and further multiplying it with the applied force. Mathematically speaking, torque can be referred by, τ = F.r. sinθ. 

Figure: 1

Further, the unit of torque is termed by Newton–meter (N-m). Quite clearly, this equation can be further classified as the vector product of force and position vector, resulting in,

τ = r x F

Now, as per how the vector product notations are mentioned, you can find the direction of torque as well. In real life, we usually confront an example of torque in automobile engines or even in the motion of a normal parachute. 

Applications of Torque

Here is where you generally find the real life instances of torque:

1. See-Saw.
2. Automobile Engines.
3. A pendulum usually follows the movement of torque by motioning a swing.
4. Gyroscopes.
5. The motion involved in cycling.

Application of Couple

The following are some of the applications of couple in real-life:

1. The steering of a car used by a driver.
2. The movement involved in opening and closing a normal facet.
3. Screwdriver.
4. Rotating the cap of a jug.
5. The movement involved in a key.

Calculation of Couple

As was defined earlier, a couple is generally a blend of two equal and parallel forces that act opposite to each other. It comes with an identical magnitude, but in an opposite direction, influenced by a perpendicular distance.

MC = r * F, this equation commonly uses vector analysis. Now, since both the forces are acting at quite a distance from one another, they form a moment. 

A moment of a couple can simply be defined as the product of either of the two forces generated by a couple by a perpendicular distance between them. 

Torque and a couple are somewhat on the same plane. Which means, they both are responsible for the production of rotational motion of an object. 

The forces we generally encounter in a couple come with the same magnitude, but in different directions, leading to the resultant force to be zero. Clearly, it does not possess any form of translational motion deemed necessary for an object.

Generally, when you rather cannot find any resultant force within a body, it is likely that the body does not possess any translational motion, leading it to remain at rest.

Things to Remember:

1. Torque and force are different but are still in the same range. In rational mechanics, it is known to be a counterpart of force. The only major difference they both have is the capability torque comes with rotating an object on its axis.
2. Since torque can be expressed as the counterpart of force, it has the ability of applying rotating and twisting forces, when and where necessary. As for a car, the engines, as a result of acceleration, rotate about its axis, forming torque. Torque helps cars, be it of any kind, speed the engine from 0-60 in seconds.
3. Torque can be expressed as a special case of moment.
4. In simple words, the torque vector clearly describes the plane upon which both the position and force vectors dwell. Following the same, the resulting torque vector direction is gradually put into conclusion by the right-hand rule.
5. Couple and torque, coincidentally, excavates identical dimensions, but they still arrive with variable purposes. For the record, the measurement utilized for couples does not necessarily link with the axis of rotation.