Wagon-wheel effect

An illusion in which a rotating wheel appears to slow, stop, or reverse direction when its motion is sampled intermittently, as in film or strobe light.

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Temporal aliasing: A sampling error in which a changing signal appears to have a different frequency or direction than it actually does. The illusion is a visual case of motion being misrepresented by sparse temporal samples.
Film: A medium that presents a sequence of still images rapidly enough to create the impression of continuous motion. A film camera can capture successive wheel positions that make rotation appear reversed.
Phi phenomenon: An apparent movement produced by stationary lights flashing in succession at different locations. It creates motion from changing positions, whereas the wagon-wheel effect misreads a genuinely rotating object.
Reverse rotation in film: The apparent backward rotation of a moving object in footage captured at discrete frame intervals. It is the familiar cinematic instance of the wagon-wheel effect.
Stroboscopic effect: The apparent slowing or freezing of periodic motion under flashes of light. A strobe supplies the discrete visual samples that can make a wheel seem stationary or reversed.
LED flicker: Rapid variation in the light output of an LED, often caused by its power supply or dimming method. Flickering illumination can act like a strobe and make moving wheels appear to change speed.
Beta movement: The perception of an object moving between successive positions when it is shown in separate frames. It explains apparent continuity in film, while the wagon-wheel effect concerns an incorrect interpretation of rotation.
Strobe-frozen wheel: A rotating wheel that appears stationary when each light flash reveals the same angular position. This demonstration shows how matching flash timing can erase visible rotation.
Nyquist–Shannon sampling theorem: A theorem specifying the sampling rate needed to reconstruct a band-limited signal without aliasing. Its sampling limit helps explain why motion sampled too slowly can acquire a false direction.
Stroboscope: A device that emits regularly timed flashes of light to inspect or measure periodic motion. Adjusting its flash frequency can freeze a wheel or make it seem to rotate backward.