# Can there be force couples in a particle system of equilibrium?

• Inertigratus
In summary, the conversation discusses the concept of equilibrium and whether or not there can be momentum in a system that is in equilibrium. The teacher explains that force couples are disregarded in a system of equilibrium and that it is possible to have a net force equal to zero while still having a net moment. The presence of a force couple in a static equilibrium also requires a negative moment of the same magnitude. It is also mentioned that it is possible for a system to have a net force and still continue in uniform motion.

#### Inertigratus

My teacher said that if a system is in equilibrium, then there cannot be any momentum. I asked, what if there are force couples?
He said that fource couples are disregarded, or they that are not possible in a system of equilibrium. If this is wrong, then I probably don't remember what he said exacty.
Hoping for a better explanation here. Can't there be two opposite forces of equal magnitude affecting the particle and therefor making the particle rotate while the system is in equilibrium?

Static equilibrium generally means both translational and rotational equilibrium. Thus, about any point the net moment of all forces would be zero.

But it's certainly possible to have the net force equal to zero while having a net moment, as you point out.

So to have a force couple in a static equilibrium it means that there also has to be a negative moment the same magnitude as that of the force couple?

Inertigratus said:
So to have a force couple in a static equilibrium it means that there also has to be a negative moment the same magnitude as that of the force couple?
Yes. Otherwise it will not be in rotational equilibrium.

@doc atleast during the couple there will be momentum change (angular) or watever...

phyeinstein_c said:
@doc atleast during the couple there will be momentum change (angular) or watever...
Not if the net moment is zero everywhere.

oh yeah.. :P I am tubelight

it is also possible that net force (moment/torque ) is 0 but it continues in uniform motion??

phyeinstein_c said:
it is also possible that net force (moment/torque ) is 0 but it continues in uniform motion??
Definitely.

ohkk... :)

## 1. What is a force couple in a particle system of equilibrium?

A force couple refers to a pair of equal and opposite forces that act on a rigid body, causing it to rotate without any accompanying translation. These forces have different lines of action, resulting in a net torque on the body.

## 2. How can force couples be created in a particle system of equilibrium?

Force couples can be created by applying two equal and opposite forces at different points on a rigid body. The forces must have different lines of action, resulting in a net torque on the body. These forces can be applied by external agents or by internal forces within the system.

## 3. Can force couples exist in a particle system of equilibrium?

Yes, force couples can exist in a particle system of equilibrium as long as the net external forces acting on the system are balanced and the net torque is also equal to zero. This means that the system is in a state of translational and rotational equilibrium.

## 4. What is the significance of force couples in a particle system of equilibrium?

Force couples are important in understanding the stability and balance of a system. They play a crucial role in maintaining the equilibrium of a rigid body and can also help in predicting the behavior of the system under different external forces and torques.

## 5. How can force couples be resolved in a particle system of equilibrium?

Force couples can be resolved by using the principle of moments, which states that the sum of the clockwise moments about any point must be equal to the sum of the counterclockwise moments about the same point. By resolving the forces and calculating the net torque, the equilibrium of the system can be analyzed.

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