  The drag acting on an intruder in a three-dimensional frictionless dry
granular environment is numerically studied. It is found the followings: (i)
There is no yield force for the motion of the intruder without the gravity.
(ii) The drag is proportional to the cross section of the moving intruder.
(iii) If the intruder is larger than surrounding grains, the drag is
proportional to the moving speed $V$ of the intruder for dense systems, but it
exhibits a crossover from quadratic to linear dependences of the moving speed
when the volume fraction of the surrounding grains is much lower than the
jamming point. (iv) There is a plateau regime where the drag is almost
independent of $V$ if the size of the intruder is identical to those of the
environmental grains and the volume fraction is near the jamming point.
