When is Momentum Not Conserved: Why, How and Detailed Facts

When is momentum not conserved when an external force is acting on the system, this external force is applied to trigger the motion in a system.

Generally, when we say that a system is under motion, it will be when several factors and quantities contribute to it. The factors will be friction, velocity, acceleration, momentum, impulse, and so many others.

For instance, in a place where snow falls in extreme and in such places we all would like to playmaking snow into snowballs and snowman, when we take a snowball and strike it on a hard surface, for example, a brick, the snow sticks to it.

So there is some momentum in the ball before striking, but the momentum is lost and becomes zero after striking. So we all can say that momentum is lost and is not conserved, but the actual detailing behind the process is different.

Considering formulas and using the velocity values when we calculate the initial and final momentum, we can see what happens there. And it is surprising is not conserved.

“SNOW MAN” by Sparticus is licensed under CC BY-NC 2.0

How do you know whether momentum is conserved or not?

When a system is under motion, it will experience as many quantities in it. One such is the momentum which is conserved at all times irrespective of the conditions that prevail to abduct the conservation.

Momentum is one primary quantity that keeps the system’s motion intact whenever needed. We know that friction is one of the quantities that stay between the body and the surface on which it is moving. We need to also must know it is a great provider to the motion.

For instance, if two bodies are under motion and are in collision with each other, then we need to look deep into the momentum part of it. The conservation of energy is altogether a whole different story but not momentum conservation.

Momentum is conserved when one body’s momentum is transferred to the other. For example, if one body having 60 units of momentum is transferred to the other body, the total momentum of the system is the same and is as well as conserved.

Why is momentum not conserved in an elastic collision?

We need to understand the concept behind the elastic and inelastic collision. In an elastic collision, momentum is conserved and the kinetic energy.

An elastic collision is one in which the total kinetic energy of the system is not lost but travels inside the system throughout. Because before the collision, the energy and the momentum are conserved, and if only after the collision is the conservation same, then it is said to be a proper elastic collision.

Momentum does not always change and not be conserved because when the kinetic energy is conserved by default, the collision is conserved automatically. The momentum required when the change of speed happens during a collision does not change. Even after the collision, it is said to be conserved.

Inelastic collision, the momentum is the mass that requires extra effort to move further with the change of speed that occurs there. The momentum may be changed or mostly transferred to the other body under collision.

Therefore we need to understand that in an elastic collision, there will be a conservation momentum and energy along with it.

What is the condition for conservation of momentum?

Firstly there must be an object that has to be under motion. Then there must be momentum in terms with it. The momentum must not be lost to be conserved.

Let us take a two-body that are in a collision, and then it is easier for us to determine whether the momentum has been conserved. So when two bodies collide, each the momentum before and after a collision must be equal, and the total momentum of the system must be equal to zero.

For example, let us consider the particle collision in terms of this. When two particles are let to collide in an isolated system, they will have their mass, velocity, kinetic energy, etc.

So when they strike each other, their momentum will change and the speed at which they are traveling; hence their energy will be conserved along with the momentum if it is an elastic collision.

Considering the collision to be inelastic, then the kinetic energy of the total system will be lost in the end. So the momentum will be transferred, but somehow they will lose each other’s momentum.

Conditions for a momentum to be conserved is that the before and after collision’s momentum must be the same and not vary even slightly.

When is angular momentum not conserved?

The angular momentum in any closed system will always be conserved since the system’s velocity and momentum. So it will always be conserved but with exceptions.

So when in any rotatory system, the angular momentum is nothing but something equivalent to the linear momentum in straight systems. So in the circulatory or any other rotatory systems, the angular momentum will be conserved.

The mass of the system directly affects the momentum and will be certainly changed for the change in speed. Since in circular motion, if there is any torque applied, then the angular momentum will undoubtedly be equal to zero.

To be conserved in a rotatory motion, this concept of angular momentum we need to refer to Newton’s Second Law. So it will tell us that if there is no internal torque in a circular motion, then the angular motion is conserved for sure.

When is momentum not conserved in a collision?

The motion of a system takes place only with the help of several quantities, namely, friction, momentum, impulse, and so many others.

When there is friction, there will undoubtedly be a loss in the momentum because the speed also matters in case of considering the conservation. So the momentum of the entire system will not be equal to zero if there is friction occurring in the system.

If the net force of a system is not equal to zero, then the momentum will not be zero. Friction usually happens when the path of the motion is rough enough; otherwise, there will be no proper hold of the body on the surface.

If the energy is not conserved in a collision, then the momentum will also not be conserved. It is because the energy in the collision system will be lost if it does not have the same momentum.

We all must be aware of Newton’s Third Law that in an isolated system, the momentum is always conserved irrespective of it being elastic or inelastic collision. So energy also has a direct influence on the conservation of momentum.

When is linear momentum not conserved in a system?

In an isolated system, when we do not apply any external force, it is said that the momentum of that isolated system is conserved.

In any system under motion, there is a necessity for an external force to be applied to a system. So here, the linear momentum is not conserved. Other factors also affect the conservation of the momentum in linear terms. That will be friction and the net force also.

When the net force of the entire system is not equal to zero, then the linear momentum is said to be conserved. But we need to understand that there must be enough friction to move the body further with proper velocity.

So mainly whenever there is an external force applied to the system, there will be a change in the speed of the body under motion, and this when is momentum not conserved.

When is angular momentum conserved but not linear momentum?

Angular momentum and linear momentum are two different types, although sharing the same root points.

We must have this basic understanding that there needs to be some external factor for the body to remain under constant motion. So for angular momentum, it deals with torque, and linear momentum, it deals with force.

When the external torque is absent, the angular momentum will be conserved despite when the linear momentum is not conserved when an external force is present. So in any circular system of motion, the angular motion can be conserved when external torque is not applied.

Even when linear momentum is not conserved, the angular momentum will be conserved because the eternal torque should not be applied at all.

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