Exercise ball a chair because of ergonomic considerations or biomechanical reasons. This large plastic ball, known as a "birth ball", can also be used during labour to aid the descent of the fetal head into the pelvis. Sitting in an upright position will also aid fetal positioning and is more comfortable for the woman. Sitting on the ball with arms placed on a bed, table or otherwise sturdy object for support and gently rocking the hips may help the woman during contractions and aid the natural physiological process of birth. Exercise ball An exercise ball, also known as a Swiss Ball, is
Rolling ball argument If the surface contains a wormhole whose throat narrows to slightly less than the ball's diameter, the ball may be able to enter and explore each wormhole mouth, but will not be able to pass through the throat, and will produce a map in which the narrowing mouth walls each terminate in a sharp geometrical spike. The smooth and multiply connected surface will be mapped by the physics of a "large" particle as being singly connected and including geometrical singularities. If the surface being explored is flexible or elastic, the way the ball is used may affect the reported topology.