The three laws of motion on which Newtonian mechanics is based. (1) A body continues in a state of rest or uniform motion in a straight line unless it is acted upon by external forces. (2) The rate of change of momentum of a moving body is proportional to and in the same direction as the force acting on it, i.e. F = d(mv)/dt, where F is the applied force, v is the velocity of the body, and m its mass. If the mass remains constant, F = mdv/dt or F = ma, where a is the acceleration. (3) If one body exerts a force on another, there is an equal and opposite force, called a reaction, exerted on the first body by the second.

Hooke’s law
The stress applied to any solid is proportional to the strain it produces within the elastic limit for that solid. The ratio of longitudinal stress to strain is equal to the Young modulus of elasticity. The law was first stated by Robert Hooke in the form ‘Ut tensio, sic vis.’