This set is unusual because it includes a tube with both a bubble, a plastic ball and a metal ball, giving the students the added twist of having an object with a negative velocity and thus a negative slope on the graph. Students can predict where the ball and the bubble will meet.
Constant Velocity Tubes effectively introduce the relationship between graphs and motion. Students can use a meter stick and a stopwatch to plot the position of the bubble as a function of time as it moves up the tube. Each tube has an obstruction that serves as the initial position for the bubble. The slope and vertical intercept from the graph yield the equation of motion.
This set includes three tubes with varying viscosities and initial starting points plus one tube with both a bubble and two balls. The red one and the colorless one have the same viscosity.https://www.pasco.com/products/lab-apparatus/mechanics/gravity-and-freefall/se-9072#specs-panel