Principles of Manual Medicine
Newton's Laws
Force can be defined as any action that tends to change the state of rest or motion of the object to which the force has been applied. Mechanics is the engineering discipline that enables us to describe the effects that forces have upon materials and objects. Biomechanics is the discipline that creates a bridge between mechanical engineering and biology, enabling physicians to better understand the effect that forces can have upon biological structures such as bone, muscle, tendon, and ligament. In order for an osteopathic physician to utilize the full potential of OMT, there must be an understanding of basic biomechanical concepts. In order to understand basic biomechanical concepts, there must be an understanding of the basic laws of physics.
Physics is built upon the foundation of Newton's laws. Newton's first law says: An object will remain in a state of rest (or of uniform motion) until it is acted upon by some external force. A desk will stay in the same location until someone pushes it to a new location. A car will continue to slide across a patch of ice until some external force acts upon it.
Newton's second law says: A rigid object (having a mass equal to m) will have a value of acceleration (a) that is directly proportional to the force (f) that is applied to it (f = ma).
Newton's third law says: For every force of action there is an equal and opposite force of reaction. Forces of action and reaction are equal and opposite in magnitude, and have the same line of action. Exhaust gases of a rocket are expelled backward (force of action) causing the rocket to be pushed forward (force of reaction). Notice that is the common word that appears in each of Newton's three laws.