Abstract
The dynamics of the sine-Gordon soliton is studied by the consideration of the breather solution of the sine-Gordon equation in the limit of large soliton separation. It is found that in this limit the sine-Gordon soliton behaves as a Newtonian particle, i.e., the acceleration of the soliton is proportional to the force acting on it. The definition of the force acting on the soliton is scrutinized.