Accelerometer - Ball In Water
To demonstrate the direction of acceleration for both linear and circular cases.
Water-filled plastic tubes with pingpong balls, as photographed.
When the accelerometer is accelerated linearly, the pingpong ball, being less dense than the water, moves toward the direction of the acceleration. When the jars are rotated the pingpong ball moves toward the center of rotation.
Richard M. Sutton, Some Dynamic Applications of Liquid Manometers, AJP 3, 77-81 (1935). J. Harris and A. Ahlgren, Apparatus: Lecture Demonstration and Laboratory. Classroom Techniques: Some Simple Experiments and Demonstrations, TPT 4, 314-322 (1966). H. R. Crane, Problems for Introductory Physics, TPT 7, 371-378 (1969). Meiners, Physics Demonstration Experiments, Volume 1, Section 8-3.8, page 146. Earl Coombs, Demonstrating the Difference between Velocity and Acceleration, TPT 28, 546-547 (1990). D. Easton, Fletcher's trolley - Alive and well, TPT 21, 184 (1983).