What term denotes the restoring force acting on gravity waves?

The term that denotes the restoring force acting on gravity waves is gravity. In the context of ocean waves, gravity plays a crucial role in the formation and behavior of these waves. When a disturbance occurs on the surface of the water, such as wind creating waves, gravity acts to restore the surface back to a state of equilibrium, causing the waves to oscillate.

Gravity-induced restoring forces are responsible for the characteristic motion of gravity waves, which involves the water surface rising and falling. This oscillation continues until energy dissipates, illustrating how gravity works to pull the water surface back down after being lifted by an external force.

The other choices relate to different aspects of ocean dynamics. Surface tension is more relevant to capillary waves, which are smaller and are influenced by intermolecular forces. Momentum pertains to the movement of water and not specifically to the restoring forces of gravity waves. Water displacement involves the movement of water due to waves but does not directly relate to the force that brings the waves back to their baseline level, which is the role that gravity fulfills.