D In order to obtain the theorem of the change in the kinetic energy, we make use of the energy method to investigate dynamical problems. In different to the cases of the theorems of the changes in the linear and the angular moment we make use of the vector method. The method not only has important applications in the research of the mechanicalmotion, but it is also the bridge connecting mechanical motion with other forms of motion .The theorem of the change in the kinetic energy establishes the dependence between the physical quantities describing motion---kinetic energy and describing the acting force work. It is a law describing changes between different forms of energy. 8 14-1 Work done by a force Work is a measure of the accumulated effect of the action of a force on a body during a given displacement 1. Work done by a constant force W=FS cos a M2 The work done by a force is a scalar quanti Fora <n, the work is positive, fora 2, the work is zero, for a>a, the work is negative. The unit of work in the SI system is the joule(). 1J=INIm5 In order to obtain the theorem of the change in the kinetic energy,we make use of the energy method to investigate dynamical problems. In different to the cases of the theorems of the changes in the linear and the angular moment we make use of the vector method. The method not only has important applications in the research of the mechanical motion, but it is also the bridge connecting mechanical motion with other forms of motion.The theorem of the change in the kinetic energy establishes the dependence between the physical quantities describing motion---kinetic energy and describing the acting force--- work. It is a law describing changes between different forms of energy. Work is a measure of the accumulated effect of the action of a force on a body during a given displacement. 1. Work done by a constant force F S W FS =  = cos The work done by a force is a scalar quantity. For , the work is positive, for , the work is zero, for , the work is negative. The unit of work in the SI system is the joule (J). 2    2   = 2    1J=1N1m § 14-1 Work done by a force