Mechanics can be founded in a principle stating the uncertainty in the position of an observable particle delta-q as a function of its motion relative to the observer, expressed in a trajectory representation . From this principle, p.delta-q=const., being p the q-conjugated momentum, mechanical laws are derived and the meaning of the Lagrangian and Hamiltonian functions are discussed. The connection between the presented principle and Hamilton's Least Action Principle is examined. For a particle hidden from direct observation, the position uncertainty is determined by the enclosing boundaries, and is, thus, disengaged from its momentum. Heat, as a non-mechanical magnitude, stem from this fact, and thermodynamical magnitudes have direct expression in the presented formalism. It is finally shown that in terms of Information Theory, mechanical laws have simple interpretation. Kinetic and potential energies are expressions of the information on momentum and position respectively, and the law of conservation of energy expresses the absence of information exchange in mechanical interactions.