# What does it mean when momentum is not conserved?

## What does it mean when momentum is not conserved?

Momentum is not conserved if there is friction, gravity, or net force (net force just means the total amount of force). What it means is that if you act on an object, its momentum will change. This should be obvious, since you are adding to or taking away from the object’s velocity and therefore changing its momentum.

### How is momentum defined in quantum mechanics?

In quantum mechanics, momentum is defined as a self-adjoint operator on the wave function. The Heisenberg uncertainty principle defines limits on how accurately the momentum and position of a single observable system can be known at once. In quantum mechanics, position and momentum are conjugate variables.

Is momentum conserved in quantum mechanics?

Energy and momentum are conserved, resulting in a reduction of both for the scattered photon. Studying this effect, Compton verified that photons have momentum. Momentum is conserved in quantum mechanics just as it is in relativity and classical physics.

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Does a free particle have definite momentum?

, Physics professor since 1977. A particle can have a definite momentum. It just can’t have a definite position at the same time.

## Is momentum always conserved?

Momentum is always conserved, regardless of collision type. Mass is conserved regardless of collision type as well, but the mass may be deformed by an inelastic collision, resulting in the two original masses being stuck together.

### What does not conserved mean?

parity
If the physical process proceeds in exactly the same way when referred to an inverted coordinate system, then parity is said to be conserved. If, on the contrary, the process has a definite handedness, then parity is not conserved in that physical process.

Why do position and momentum not commute?

The position and momentum operators do not commute in momentum space. The product of the position‐momentum uncertainty is the same in momentum space as it is in coordinate space.

How do you find the momentum of a quantum particle?

This is the essence of measurement in quantum mechanics. Classical momentum can be obtained simply by measuring the time an object takes to pass between two stationary detectors (‘time-of-flight’), finding the velocity and multiplying by the mass.

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## Why momentum is conserved?

Impulses of the colliding bodies are nothing but changes in momentum of colliding bodies. Hence changes in momentum are always equal and opposite for colliding bodies. If the momentum of one body increases then the momentum of the other must decrease by the same magnitude. Therefore the momentum is always conserved.

### Does free particle have definite energy?

In his textbook, Griffiths states “there is no such thing as a free particle with a definite energy”.

What will be the effect on potential energy for a free particle?

A Free Particle. A free particle is not subjected to any forces, its potential energy is constant. Set U(r,t) = 0, since the origin of the potential energy may be chosen arbitrarily.

Why is momentum not conserved in an elastic collision?

An inelastic collisions occurs when two objects collide and do not bounce away from each other. Momentum is conserved, because the total momentum of both objects before and after the collision is the same. However, kinetic energy is not conserved. In an elastic collision, both momentum and kinetic energy are conserved.

## What is the quantum mechanical uncertainty principle for position and momentum?

According to quantum mechanics, the more precisely the position (momentum) of a particle is given, the less precisely can one say what its momentum (position) is. This is (a simplistic and preliminary formulation of) the quantum mechanical uncertainty principle for position and momentum.

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### Can we know the exact values of momentum and velocity simultaneously?

I know that by Heisenberg’s Uncertainty Principle that it is not possible to know the exact values of position and momentum of a particle simultaneously, but can we know the exact values of momentum and velocity of a particle simultaneously?

What is the angular momentum of a particle?

It describes how much a particle rotates (like the linear momentum describes how much a particle moves ). And there exists a conservation law of angular momentum too. It’s because of this law, that eventually one came up with the spin of a particle, also called spin angular momentum.

What does momentum mean in physics?

When you hear momentum, one means the linear momentum of a particle. It’s a measure for how much a particle moves. Mathematically (and according to classical mechanics): , in words: mass times velocity. It’s intuitively a very useful concept: comparing two objects with the same velocity, but different mass,…