The correct option is Friction occurs between the dynamic water and the sea floor..
Explanation
Ocean waves represent the movement of energy through water. In deep water, the water particles move in circular orbits that do not interact with the ocean bottom. However, as waves approach the coast, they transition from deep-water waves to shallow-water waves.
Detailed Analysis:
- Friction with the Sea Floor: When waves enter water where the depth is less than half of their wavelength, the orbital motion of the water particles begins to interact with the sea floor. This interaction generates friction between the dynamic water and the bottom sediment.
- Impact on Speed: This frictional drag resists the motion of the wave, causing the wave speed (celerity) to decrease.
- Consequences (Shoaling): As the leading part of the wave slows down while the trailing part maintains speed, the wavelength shortens (the waves bunch up). To conserve energy flux, the wave height increases. Eventually, the wave becomes too steep and breaks as surf.
Analysis of Incorrect Options:
- The wind speed decreases significantly near the coast.: While wind generates waves, a local decrease in wind speed near the coast is not the physical mechanism responsible for the hydrodynamic slowing of the wave itself.
- The gravitational pull of the land counteracts the wave motion.: The gravitational pull of the land mass is negligible compared to the hydrodynamic forces and Earth's gravity acting vertically on the water column.
- The density of water increases near the shore.: The density of seawater does not increase significantly near the shore in a manner that would mechanically slow down wave propagation.
Key Takeaway:
The reduction in wave speed near the coast is primarily caused by friction between the water particles and the sea floor as the water depth decreases, a phenomenon central to shallow-water wave dynamics.