Keep your eye on the tank: A fresh look at an accelerating frame demonstration

Abstract

A water tank sliding down a frictionless ramp is a classic example of an accelerated reference frame. Along with other accelerated frames, Bartlett analyzed frictionless sliding, and showed that the liquid's surface is parallel to the surface of the ramp, rather than the base. Duzen and coworkers used liquid in an accelerating tank to help students explore motion, noting that the ramp case and riding on a cart accelerated by a hanging mass are equivalent. Munera used the second as a lecture demonstration. In both Refs. 2 and 3, students viewed accelerating tanks from the lab frame, which may be hard to observe at a distance. As the goal of these demonstrations is to understand the effects of the acceleration in the tank frame, tank-frame observations would be beneficial. Following Krulj and Slisko, a camera was mounted to an accelerated object to make in-frame videos of liquid-based equivalence principle demonstrations. Previous work did not quantify the actual acceleration of the tank; use of a Smart Cart simplifies this measurement.