Energy and equilibrium
Although the engineer conventionally expresses his ﬁndings in terms of force, deﬂection, stress, strain and so on, these are simply the convention. Fundamentally, what he is really dealing with is energy. Any change, no matter how simple, involves an exchange of energy. The mere act of lifting a beam involves a change in the potential energy of the beam, a change in the strain energy held in the lifting cables, an input of mechanical energy from the lifting device which is itself transforming electrical or other energy into kinetic energy. The harnessing and control of energy is at the heart of all engineering.