Final answer:
Organelles may not move to the bottom of a centrifuge tube when the centrifugal field's angular velocity is not high enough or when their mass is similar to the surrounding medium, preventing sufficient centripetal force from acting on them.
Step-by-step explanation:
Organelles might not move to the bottom of a centrifuge tube in a centrifugal field under certain circumstances during differential centrifugation. If the centrifugal field is not strong enough due to insufficient angular velocity, the inertia may not be enough to drive the organelles towards the tube wall to provide the necessary centripetal force for sedimentation. Another scenario is if the organelles have similar mass to the surrounding medium, which may prevent them from settling. Centrifuges operate based on the inertial effect, where the centrifugal force generated by rapid spinning causes the sedimentation of the sample. Without adequate speed, there is no significant inertia, and without difference in density or mass, particles might not separate clearly.