F maW mgg_{c}FORCE AND WEIGHTApplication of Newton's LawsCP-04 Page 2Rev. 0ForceForceis defined as a vector quantity that tends to produce an acceleration of a body in the directionof its application. Changing the body's velocity causes the body to accelerate. Therefore, force canbe mathematically defined as given by Newton's second law of motion (Equation 4-1).(4-1)where:F=force on object (Newton or lbf)m=mass of object (Kg or lbm)a=acceleration of object (m/sec or ft/sec )2 2Force is characterized by its point of application, its magnitude, and its direction. A force that isactually distributed over a small area of the body upon which it acts may be considered a concentratedforce if the dimensions of the area involved are small compared with other pertinent dimensions.Two or more forces may act upon an object without affecting its state of motion. For example, abook resting upon a table has a downward force acting on it caused by gravity and an upward forceexerted on it from the table top. These two forces cancel and the net force of the book is zero.This fact can be verified by observing that no change in the state of motion has occurred.WeightWeightis a special application of the concept of force. It is defined as the force exerted on anobject by the gravitational field of the earth, or more specifically the pull of the earth on the body.(4-2)where:W=weight (lbf)m=mass (lbm) of the objectg=the local acceleration of gravity (32.17 ft/sec )2g=a conversion constant employed to facilitate the use of Newton's second law ofcmotion with the English system of units and is equal to 32.17 ft-lbm/lbf-sec^{2}Note that g has the same numerical value as the acceleration of gravity at sea level.c