Sandy beaches are shaped by how sand moves in water and on land. Scientists study different ways sand moves and how fast it goes. They look at waves, currents, and other forces that push sand around. They also think about what the sand is made of and how it moves along the beach. Some sand stays on the bottom, while some floats in the water. Scientists have found that sand moves differently depending on where you are on the beach. They don't have a complete model yet, but they are working on it.