Humans create thrust when they swim by dragging their arms and legs through the water. Thrust can also create lift. The thrust that propels a tuna, whale, or porpoise rapidly through the water is provided by the lift created as its tail oscillates back and forth. Viscosity Fluids such as air and water are different from solids in their ability to flow. How rapidly a fluid flows, or is deformed by a given driving force, is determined by the fluid s viscosity.
Water is much more viscous than air.
Viscosity depends on temperature of both air and water, but in opposite directions. Seawater is slightly more viscous than fresh water. Moving in Air, Moving in Water Water s viscosity has a profound effect on locomotion for smaller organisms like protozoa. These organisms must overcome viscous drag, but they must also rely on viscosity to provide their thrust. The Microscopic Movement exhibit explores how these tiny aquatic organisms get around.