Where there are no opposing forces, a moving body needs noforce
to keep it moving with a steady velocity ( Newton's first law of
motion ). If, however, a resultant force does act on a moving
body in the direction of its motion, then it will accelerate (
Newton's second law of motion ) and the work done by the force
will become converted into increased kinetic energy in the body.
In order to calculate the kinetic energy of a body of mass m
moving with velocity v, we begin by supposing that the body
starts from rest and is acted upon by a force F ( no friction or
other forces acting ). This force will give the body a uniform
acceleration a, and will acquire a final velocity v, after
travelling a distance x. These quantities, a,v and x will be
related by the equation v² = u² + 2 ax In accordance with the
law of conservation of energy, the work done by the force F in
pushing the body through distance x will become converted into
kinetic energy of motion in the body. work done = force ×
distance = F × x F = ma the