As a result, a potential flow is characterized by an irrotational velocity field, which is a valid approximation for several applications.

It is therefore impossible to satisfy both boundary conditions, so is not a valid approximation to make across the whole of the domain (ie.

Although this is not an exact calculation, they considered it a valid approximation given our circumstances.

Additionally, the hadron is in a reference frame where it has infinite momentum - a valid approximation at high energies.

Newtonian mechanics is exactly revealed to be an approximation to reality, valid to great accuracy at lower speeds.

The symmetry of "conformal invariance" provides a valid approximation at very high energies or short distances when particle masses can safely be ignored.

This is a valid approximation when the applied electromagnetic radiation is near resonance with an atomic transition, and the intensity is low.

For more details that show how to obtain the uniformly valid approximation, see method of matched asymptotic expansions.

In fluid dynamics, the Boussinesq approximation for water waves is an approximation valid for weakly non-linear and fairly long waves.

The frequency dispersion characteristics of a Boussinesq-type of equation can be used to determine the range of wave lengths, for which it is a valid approximation.