These tubes can be used by students to improve their graphing skills by generating position vs. time data graphs. Three of the 34-inch tubes contain colored, oil-based liquids of differing viscosities and an air bubble. The bubble trapped in each of the liquids rises at a constant velocity that is determined by the viscosity of each liquid. The fourth tube contains a colorless oil and two spheres of differing materials. This introduces the concept of 'negative' velocity and allows for three different velocities from one tube! Requires a meter stick and stopwatch or similar.