How does Link::SetLinearVel(const math::Vector3 &_vel) achieve the link velocity?

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So the velocity is directly assign as the object variable lvel, but on every step the ODE physics engine computes the movement of the object by not only taking this velocity, but also considering the forces acting on the object

rhscurr[RHS__L_MIN + j] = -(b->facc[dV3E__AXES_MIN + j] * body_invMass + b->lvel[dV3E__AXES_MIN + j] * stepsizeRecip);

where b is the body (object), b->facc is the accumulated forces and b->lvel is the assigned linear velocity. That's why the object does not maintain the assigned velocity if there is another massive body being pulled by it.