[ODE] Frame rate problem: does sum of applied small forces equal to once applied total force in ODE ?

[Dmitry Medvedev]

 Hello.

  I apply a moment force to the body ( rolling ball on the plane) every callback. So the force applied is equal to the (force * deltaTime) in order to maintain the same behavior in different speed platforms. Where deltaTime - is a time between callback calls. Meanwhile, physics steps are called after add force with model time ( so I can be sure that the amount of physical cycles is the same in different computers). 
 Physical model_time_step decrease gives much time to others like update, where addForce * deltaTime occurs,  drawing, etc. 
  
  The problem is that changing model_time_step change speed of objects moving, it can be only if sum of applied small forces over some time amount is not equal to the total force (sum of those applied force), applied once. Is it so? 

 If so, then how maintain frame rate independence?


Thanks.