This exercise examines the correlation between gravitational-force (g-force) tolerance and the sizes of organisms, emphasizing differences between vertebrates and invertebrates, particularly the effects of size and scale on biological processes. Students form a hypothesis based on background information and then test it by spinning subjects in a centrifuge. Class results can be graphed, analyzed, and compared to human tolerance. The activity engages students in scientific process while investigating the effects of physical forces on structure and function.