The moment in beam theory is represented as the product of bending stiffness and curvature because higher curvature indicates greater deformation of the material, leading to a larger applied moment. The relationship is derived from Euler-Bernoulli beam theory, which connects bending moments to curvature through the material's stiffness properties. Understanding this derivation involves examining how changes in curvature affect the internal forces within the beam. The curvature essentially quantifies the degree of bending, which directly influences the moment experienced by the beam. This relationship is crucial for accurately predicting the behavior of beams under various loading conditions.