The bar rotates counterclockwise. Particles pass to the right of the center (as viewed from the end of the bar from where the particles are thrown toward the center).
The particles are shown with different colors and with their sizes decreasing in time as they move away from their source on the end of the rotating bar. These are visual aids to help follow individual particles as they move. If the time is increased too rapidly, the particles can appear to move backwards toward the source—in that case, changing the time more slowly will show their actual behavior of moving from the source toward the boundary of the circle.
Snapshot 1: high particle creation rate approximates behavior of a fluid squirting from the end of the bar toward its center
Snapshot 2: low particle creation rate allows seeing each particle move in a straight line when viewed in the inertial reference frame
Snapshot 3: particles follow a curved path when viewed in the rotating reference frame (where the bar does not move)
This Demonstration was inspired by a rotating fluid demonstration at Queensland Museum Sciencentre, Brisbane, Australia.
