# Newton's laws of motion

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## Newton's laws of motion

three laws that relate the forces and motions of bodies or objects (from the viewpoint of a fixed observer), first proposed by Isaac Newton. (1) An object will remain at rest or continue with constant velocity unless acted on by an unbalanced force. (2) The rate of change of momentum (or acceleration for a body/object of constant mass) is proportional to, and in the same direction as, the force applied to it (force = mass ×1 acceleration). (3) When two objects are in contact, the force applied by one object on the other is equal and opposite to that of the second object on the first (for every action, there is an equal and opposite reaction).## law

principle or rule** ***Davis' law* soft tissues' tendency to shorten and contract unless subject to frequent stretching

** ***Hilton's law* a joint and its motive muscles (+ insertions) are all supplied by the same nerve

** ***Hook's law* tissue strain (i.e. change in length) is directly proportional to applied compressive or stretching stress, so long as tissue elasticity (recoil ability) is not exceeded

** ***inverse-square law* radiation intensity is inversely proportional to square of distance from radiation source (rad = κ1/cm^{2})

** ***law of excitation* muscle tissue contracts in direct proportion to stimulating current strength

** ***Newton's first law; law of inertia* an object at rest will not move until acted upon by a force; an object in motion will remain in motion at constant velocity until acted on by a net force

** ***Newton's second law; law of acceleration* acceleration is directly proportional to applied force and indirectly proportional to object mass (i.e. force = mass × acceleration)

** ***Newton's third law; law of reciprocal actions* to every action there is an equal and opposite reaction; i.e. a body is maintained at rest by equal and opposing forces

** ***Pascal's law* a fluid at rest transmits pressure equally in every direction

** ***Poiseuille's law* vascular blood flow is inversely proportional to fourth power of vessel radius (i.e. the narrower the vessel, the greater the resistance to flow)

** ***Starling's law* the greater the stretch imposed on a circular muscle (e.g. muscle layer of an artery), the greater its reciprocal recoil and contraction

** ***Wolff's law* bone function changes cause bone structure modification (*see* bone modelling)