Move object with physic with drag

Hi, i want to move an object using physics. At the moment, i'm using

 rBody.AddRelativeForce(new Vector3(0, 0, forwardInput * forwardVelocity), ForceMode.Force);

with a forwardVelocity of 100, and a drag of 10, the object reach a max speed of 10 and than keep this value. Why? I'm adding a force every frame, i'm not doing that if velocity is lower than 10.