Many factors may contribute to the various shapes. These include the configuration of the arc terminals, gravitational and magnetic forces, and interactions between the plasma and ambient pressures. The area over which the current flows into the arc terminals (anode and cathode spots) has a strong effect on the arc configuration and on the flow of heat energy into these terminals. The current density at the workpiece terminal is of utmost importance to the size and shape of the fusion zone as well as to the depth of fusion in a welded joint.