# If a particle and a system have zero momentum

• DJW
In summary, momentum is a measure of an object's motion that takes into account both its mass and velocity. A particle is a small, localized object that can be described by its position and other physical properties. If a particle has zero momentum, it means that it is either not moving or is moving at a constant velocity. A system in physics refers to a collection of objects or particles being studied together, including interactions and relationships between them. It is possible for a system to have zero momentum if the total momentum of all particles within the system is equal to zero, which could occur due to various reasons.
DJW
Is it true that they both must also have zero kinetic energy?

If we are talking of one particle, and it has zero momentum, it must have zero velocity (mass cannot be zero), and so its kinetic energy is zero.
If a system of particles has zero momentum, anyone particle in the system may still have momentum, say ,if it is vibrating in a lattice, but the system as a whole does not.

No, it is not necessarily true that if a particle and a system have zero momentum, they must also have zero kinetic energy. Kinetic energy is a measure of an object's motion, while momentum is a measure of an object's mass and velocity. It is possible for an object to have zero momentum, meaning it is not moving, but still have some amount of kinetic energy due to its internal motion or vibrations. Similarly, a system can have a net momentum of zero if the momenta of its individual particles cancel out, but the particles may still have kinetic energy due to their internal motion. Therefore, while zero momentum may indicate a lack of overall motion, it does not necessarily mean that there is no kinetic energy present.

## 1. What is momentum?

Momentum is a measure of an object's motion, taking into account its mass and velocity. It is a vector quantity, meaning it has both magnitude and direction.

## 2. What is a particle?

A particle is a small, localized object that can be described by its position and other physical properties. It is often used to describe individual atoms, molecules, or subatomic particles.

## 3. What does it mean for a particle to have zero momentum?

If a particle has zero momentum, it means that it is not moving or is moving at a constant velocity. This could be due to its mass being zero, its velocity being zero, or both.

## 4. What is a system in physics?

A system in physics refers to a collection of objects or particles that are being studied together. This could include interactions and relationships between the objects within the system.

## 5. Can a system have zero momentum?

Yes, a system can have zero momentum if the total momentum of all the particles within the system is equal to zero. This could occur if the particles are all stationary, moving in opposite directions with equal momentum, or if the net momentum is canceled out by the interactions within the system.

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