# About Principle of Consevation of Momentum

If the net external force $$F^{\text{ext}}$$ on an $$N$$ - particle system is zero, the system's total momentum $$P$$ is constant.

This is the Principle of Consevation of Momentum.

But I think the net external force $$F^{\text{ext}}$$ on an $$N$$ - particle system is always non-zero in the real world.

Is the Principle of Consevation of Momentum nonsense?

Is the Principle of Consevation of Momentum an example of vacuously true statement?