How Fast Do Sediment Grains of Different Sizes Settle?

In this activity, students will examine water turbidity as a function of sediment grain size and the rate at which it settles out of the water. They will define rate, turbidity, and settling rate and explain the relation between settling rate and turbidity; make semi-quantitative observations of turbidity and make a graph showing change in turbidity against time; and explain how and why settling rate varies with grain size. Students can also predict how the clarity of water in a stream or in the ocean will differ during periods of high or low water flow such as during a storm or during calm weather, and explain the basis for this prediction. Educational levels: Middle school, High school