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Last updated date: 16th May 2024
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Definition of Couple in Physics on Vedantu

Students can define couple in Physics within a few lines of explanation. When two equal and parallel forces act opposite to each other, then they both create a couple.

There's no ambiguity in understanding the couple definition Physics. A couple has the only effect of producing or preventing the turning effect of the body.

A couple can be calculated with the help of the product of the magnitude of both forces & the perpendicular distance between the forces’ line. These force lines are also called action lines.  

Couple Moments Physics

When you try to understand and define couple, the steering wheel of an automobile can be the best option. It would help if you had hand forces to create a couple. Also, the application of a screwdriver twisted by your hand is responsible for the creation of a couple.

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A couple in Physics is a twisting force that does not allow any kind of moment, turning effect throughout the entire process of force engagement. 

This is a different type of force that comes with the application of two other forces. These two forces are responsible for the twisting of an object. A couple is dependent on certain other methods such as several forces, their directions, methods, their nature.

Application of Couple in Physics

You can know different types of applications for couples. Some of them are given hereunder:

  • Steering wheel applied by the car driver

  • Opening and closing of a water tap

  • Winding the spring of an alarm clock

  • Unlocking the locker by using a key 

  • Opening and closing of a cap of a water bottle, or jug.

  • Turning of a screwdriver

Difference Between Couple and Moment

Students can understand the actual difference that lies within a couple and moment with the help of the given table:



1. Couple depends upon the axis of rotation.

2. It is relying on the point of application of the force. 

3. It has the highest role to create translational motion.

4. Friction is necessary here. 

5. Rotational effect can be equalized with the help of a single proper force or a proper couple.

1. Moment depends upon the two forces only. It is not relying on the axis of rotation.

2. It is not dependent on the point of application of forces.

3. It is not responsible for any translational acceleration.

4. Friction generates two additional accelerations such angular and rotational acceleration.

5. Rotational effect can be stabled only by another proper couple of equal and opposite torque.

Couple Force Formula

As we know, a couple is the combination of two parallel forces that have identical magnitude but opposite directions distinguished by a perpendicular distance.

M\[_{c}\] = r * F

The above formula is using vector analysis. As both of the forces are acting at a distance, they create a moment. This is called a moment of a couple.

We can name a couple as torque also. It is responsible for the development of the rotational motion of a body. Forces that are involved in a couple have the same magnitude but different directions. 

This is why the resultant force is zero. When you don’t find any resultant force acting on the body, the body won’t possess any type of translational motion.

When there is no translational motion, then the body is at rest. According to research, the moment of the couple in the same plane about any point is not equal to zero. As a result, we obtain that the body is under rotational motion. 

Couple vs Torque

Torque and work have identical dimensions. However, they are not the same if we consider their physical quantities. The moment of force is a vector quantity, whereas work is a scalar quantity. 

It is coincident that both of them possess identical dimensions, but their purposes are completely different. The measurement of the couple is not linked with the axis of rotation. That is why couple and torque both are independent of the axis of rotation.

However, the magnitude of a couple is constant. When a body is under translational equilibrium, the resultant force acting on that body is zero.

Mathematically, we can write it as

ΣF = 0

This expression is ideal for an equilibrium body.

Also, when a body comes under the influence of rotational equilibrium, then the resultant moment acting on a body should be zero. The moment also has the same impact when it has no rotational motion:

ΣM = 0

Force Couple Examples

When the forces caused due to two hands help to turn a steering wheel are considered the best example of a couple. 

Each hand grips of a driver on the wheel at different points have an impact over the shaft. When a driver applies a force, then an equal amount of magnitude and opposite direction helps to rotate the wheel. The movement of screwdrivers is also another example of a couple.

What is the definition of a couple?

A screwdriver is twisted by the equivalent of a couple of hand forces, whereas an automobile's steering wheel is spun by a pair of hand forces. In contrast, a wrench is operated by a force exerted at only one end, resulting in an imbalanced force on the element being tightened in addition to the turning moment.

A couple is a pair of equal parallel forces pointing in opposite directions in mechanics. The only thing a couple can do is cause or prevent a body from turning. The amount of either force is multiplied by the perpendicular distance between their action lines to compute the turning effect, or moment, of a pair.

The Couples' Characteristics

  • The couple does not induce translational motion because the two forces that make up the couple are equal and opposing.

  • When it is applied to a body, the net resultant force is zero.

  • Because the algebraic sum of the moments of the two forces around any point in their plane is not zero, it causes pure rotational motion in the body.

  • The size and direction of a couple's moment about any point on its plane are both constant.

The Couple's Moment

The moment of the pair is described mathematically as the product of the force and the perpendicular distance between the two forces' lines of action. The arm of the Couple refers to the perpendicular distance between the lines of action of two forces. That is, the product of the applied force and the arm of a pair of forces equals the moment of force.

As a result, the moment of a pair of forces is equal to,

Τ = F × D

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The moment of a pair of forces will be bigger if the formula for the moment of a pair of forces is followed.

  • The force's magnitude is bigger, and

  • The arm of the pair of forces is longer, indicating that the perpendicular distance between the two forces' lines of action is greater.

The Newton-Meter is the SI unit for Couple Moment (N m). The dimensional formula for the Moment of Couple is \[\left [ ML^{2}T^{-2} \right ]\].

Couple Moments of Various Types

A couple of moments can be divided into two categories:

Positive moment: When the body rotates in an anticlockwise direction under the impact of a Couple, the moment is said to be positive.

Negative moment: The moment is considered to be negative when the force pair spins in a clockwise direction.

FAQs on Couple

1. How do you Define Equivalent Force?

When two forces have the same magnitude and direction, they are called comparable forces. They should also produce the same momentum at any given point. This equal force should follow the same path as the original force. All the concepts, key features, advantages and disadvantages can be well studied with the help of a free PDF of Couple in Physics from Vedantu. You can know about the concepts and get a better grip on the topics.

2. What is the Formula for Work?

Work is a physical metric that measures the overall amount of effort exerted by the body or body parts. By multiplying the force and the distance, we get the work done (movement of the object). W = F × d (SI unit of work is Joule). Students are required to practice the problem equations based on the formula for work and use them in their daily life. The more problem solutions you solve, the better knowledge you will get. One can practise this equation problem sums with the help of our online coaching classes and get help from our professional team of experts.

3. How Do You Define Torque? Mention its SI Unit.

Torque is a physics term for the force that can cause an object to rotate around its axis. The formation of angular acceleration is due to torque. Torque is used when turning the steering wheel of an automobile or opening the cap of a water bottle. The SI unit of torque is Newton-metre. Torque is an important concept in class 11th and 12th. Students should get a better grip on these topics and solve the problem equations based on the same. It can come up in your entrance examinations like JEE or NEET. The more practice you will do, the easier the concepts will be.

4. Give one example of a force couple?

The most famous and best example of the force couple is operating a steering wheel while driving. The drivers usually take a U-turn with the help of both hands and push the steering wheel in the direction. It is a classic example of force coupling. Each hand has a different force with each finger of the hand. When a driver applies a force, then an equal amount of magnitude and opposite direction helps to rotate the wheel. Hence students will be able to learn about the force coupling through daily life examples.

5. What are the factors on which a couple depends?

The couple mainly depends upon the axis of rotation in physics. The point where the force started all the application of the force is also a contributing factor to the couple. It has a contributing role to creating translational motion and friction is said to be necessary. With the help of a single proper force or a proper couple, one can equalise the rotational effect too. All these factors contribute to coupling. You can study the concepts and features of the same with the help of a free PDF- Couple in Physics.

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