Download PDF

Bookmark added to your notes.
View Notes

Define Couple

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. 

[Image will be Uploaded Soon]

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 direction distinguished by a perpendicular distance.

MC = 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.

FAQ (Frequently Asked Questions)

Q1. How Do You Define Equivalent Force?

Ans: Two forces are called equivalent forces when both of them have an identical magnitude and direction. Also, they should produce an identical moment about any point. This equivalent force should act on the same line of action.

Q2. What is the Formula for Work?

Ans: Work is a physical parameter used to determine the total effort done by the body or body. We can calculate work by multiplying the force and the distance (movement of the object).

W = F × d (SI unit of work is Joule)

Q3. How Do You Define Torque? Mention its SI Unit.

Ans: Torque is used in physics for the measurement of the force that can make an object rotate about its axis. Torque is responsible for the creation of angular acceleration. Turning the steering of the car or opening the cap of a water bottle has the involvement of torque. SI unit of torque is Newton-meter. 

Q4. Find a Couple of Forces of the Circular Discs, If it is in Motion Due to the Force 5 N with a Distance of 3 Meters.

Ans: Data given, 

Force, F = 5 N

Distance d = 3 m

Couple, MC = d * F = 3 * 5 = 15 N-m