what is stroboscopic effect?

Answer 1

Temporal aliasing is the term applied to a visual phenomenon also known as the stroboscopic effect. It also accounts for the "wagon-wheel effect", so called because in video or motion pictures, spoked wheels on horse-drawn wagons sometimes appear to be turning backwards.

Temporal aliasing is one example of a range of phenomena called aliasing that occur when continuous motion is represented by a series of short or instantaneous samples. It occurs when (a) the view of a moving object is represented by a series of short samples as distinct from a continuous view, and (b) the moving object is in rotational or other cyclic motion at a rate close to the sampling rate.

source: wikipedia

Answer 2

A stroboscopic effect occurs when a series of events is viewed through a device which filters out many of the instant view-moments. So, if there were ten events (a person taking ten strides, say) but a filter prevented you seeing 9 of them, then the legs would be seen to be striding along at a different speed. O.K.? Now, the "apparent "speed might appear to be faster or slower than the real thing, which is why the car-wheels in movies seem to slow down, go backwards, and phenomona like that, while the car actually travels forward. But it can also be used positively, for instance to slow down the apparent movement of insects' wings, or humming birds, or seagull's wings, and then you can study exactly what movements they make, to allow them to fly. I used to use strobes to view vibrating propellor blades, and turbine blades, and observe how they went into resonance and finally snapped. That was at Rolls-Royce.