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
Q-ball can have an energy per unit charge that is less than formula_21, meaning that it cannot decay into a gas of individual particles. Such a region is a Q-ball. If it is large enough, its interior is uniform, and is called "Q-matter". (For a review see Lee "et al." (1992). The thin-wall Q-ball was the first to be studied, and this pioneering work was carried out by Sidney Coleman in 1986. For this reason, Q-balls of the thin-wall variety are sometimes called "Coleman Q-balls". We can think of this type of Q-ball a spherical ball of nonzero vacuum expectation value.