While designing some engineering construction (let it be a bridge) it is important to analyze not only static tensions but also dynamic deformations.
For example, it is vital to know the behavior of a bridge while earthquake.
In dynamic problems we are looking for solution of deformations equation as a function u(x,y,z,t) not only space coordinates x,y,z, but also as a function of time t. This makes a problem on at least one degree more complicated.
Look on this video to have a feeling of the ptoblem…