A SIMPLE STOKE’S LAW LABORATORY ACTIVITY FOR USE IN MULTIPLE STEM DISCIPLINE COURSES

Climate change, population growth, and political variation all contribute to an ongoing need for a stronger public understanding of water resource issues. Knowing the rate at which sediments settle is important in the development of settling basins, the study of fertilizer runoff, and the management of wastewater treatment plants. When students complete this activity, they gain experience in data collection, properties of minerals and fluids, quantitative analysis of data, and application of results. Students enrolled in geoscience, environmental studies, and mathematics courses have successfully completed the activity in addition to high school students participating in outreach events.

In this hands-on project, students collect data on the rate of sedimentation and are guided through the process of determining the formula for Stoke’s Law. The activity, including completion of data analysis, can be completed within a 2.5-hour laboratory period. The activity improves students’ ability to collect and analyze data and deepens their understanding of direct and inverse variation. Challenging portions of this process and common student errors in collecting data and in using Excel will be presented.

Students are provided with quartz and galena particles that are graded to ¼ phi increments that allow students to observe how particle size and density affect the settling rate within 1000 ml soil hydrometer sedimentation cylinders. Quartz and galena were chosen because the particles tend to be roughly equidimensional and differ greatly in density. Data collected include the water temperature, the particle size and density, and the distance and time required for particles to settle.

Fluid properties can also be modified through temperature changes and the addition of dissolved solids. If adequate time is available the limitations of Stoke’s Law can be illustrated by using larger particles or platy particles (such as micas). Students are asked to predict how changes in fluid and particle properties will affect the settling rate—later they evaluate if their analysis of the data supports their predictions.

This lab allows students to gain a sense of ownership of Stoke’s Law by connecting their data to the development of the formula and to practical applications involving settlement rates for sediment.