IB Marine Science Standard Level (SL) Practice Exam 2026 - Free Marine Science Practice Questions and Study Guide

The main idea is how water moves under a surface wave. In an orbital wave, water particles move in circular paths that get smaller with depth—the influence of the wave fades as you go down. The surface crest travels forward while the particles bob in these diminishing circles, so the energy moves along the surface while the water itself mainly oscillates locally. In deep water the circles are nearly full and symmetric, while in shallower water the motion becomes elliptical and is limited by the bottom. This description fits orbital waves, whereas a progressive wave emphasizes the traveling shape of the wave, and the others refer to different sea states or unusually large waves.