Body and surface forces, sedimentation and convection

Objective: Provide a quantitative demonstration that shows how the rates of settling are related to body and surface forces.

Demonstration: Fill the cylinder with glycerol and measure the rate at which the spheres settle. Observe over what distance they reach terminal velocity. Talk about the reason for the different settling rate and measure the rate at which the spheres settle. Make a plot and have the students figure out the reason for the results.
Note. I do this demonstration usually before talking about thermal convection. During thermal there is the added effect of the rate of cooling, also a surface controlled phenomenon.

Illustrated here is a graduated cylinder filled with glycerin, and containing teflon balls. The balls will sink slowly when added to the cylinder. The textbook page describes the principles of isostasy.