Density Rainbow and the Great Viscosity Race
Figure 1. Rainbow created by fluids of different densities.
Students explore the densities and viscosities of fluids as they create a colorful 'rainbow' using household liquids. While letting the fluids in the rainbow settle, students conduct 'The Great Viscosity Race,' another short experiment that illustrates the difference between viscosity and density. Later, students record the density rainbow with sketches and/or photography.
Fluid properties are important in the design of any device that interacts with a fluid, either liquid or gas. Knowledge about density inspired engineers to build ships, inner tubes, surfboards, buoys and other flotation devices, while the understanding of viscosity allows engineers to build not only ships that float, but also ships that can travel fast, and airplanes that can fly at supersonic velocities. Density and viscosity are also important properties that engineers consider in the engines they design for automobiles and power plants.
After this activity, students should be able to:
- Define density and viscosity.
- Compare and contrast density and viscosity.
- Represent density and viscosity by their equations and define all parts of each equation.
- Notice that viscosity is dependent on density, but can be smaller or greater based on temperature, so they are not proportional.
- Explain why it is useful to know how to calculate density and viscosity.
- Give examples of how engineers use this information, such as in flight (real world examples).
- See that visualizing a fluid flow can both show the physics that are occurring, and be beautiful.