The loss factors for sudden contraction, sharp-edged entrances, and nozzles involve two phenomena: turbulence, which has been discussed, and stream contraction. Because of inertia, an element of fluid does not necessarily follow the walls of the retaining structure. For example, the stream of water after leaving the point of sudden contraction in Table 2.3 is smaller in diameter than the pipe and has a velocity higher than it has farther along in the pipe. The point at which this stream diameter is a minimum is called the vena-contracta. Vigorous turbulence in the region of the vena-contracta between the wall of the pipe and the flowing stream, i.e., when there are no reverse eddies, causes considerable energy loss. A rounded approach avoids the formation of a vena-contracta, and a cone of expansion with a slope angle of 7 degrees or less permits a change in velocity with a minimum energy loss. For a detailed study of these losses, the reader should refer to a textbook on fluid mechanics or to detailed specialized reports