Calculating forces in moving objects is important, especially for electric motors and other moving electromagnetic devices. When performing the computations in a coordinate system that moves with the object, the electromagnetic fields are transformed. The most well-known relation for moving objects is the one for the electric field. The transformed quantity of the electric field is called the electromotive intensity.

Assume that the object modeled is moving with a constant velocity, v = v0. The equations now take on a slightly different form that includes the Galilei invariant versions of the electromagnetic fields. The term Galilei invariant is used because they remain unchanged after a coordinate transformation of the type

The electromotive intensity is the most important of these invariants. The Lorentz magnetization is significant only in materials for which neither the magnetization M nor the polarization P is negligible. Such materials are rare in practical applications. The same holds for the magnetization term of the magnetomotive intensity. Notice that the term ε0v × E is very small compared to B/μ0 except for cases when v and E are both very large. Thus in many practical cases this term can be neglected.

where D = ε0E and B = μ0H.

The terms containing v × B cancel out, which yields the following equation:

The magnetization M and the polarization P occur explicitly in this expression.