Why do ripples appear to move backwards with a higher strobe frequency?

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SUMMARY

The discussion explains the stroboscopic effect, where water ripples appear to move backwards when the strobe light frequency exceeds the ripple frequency. Specifically, if ripples advance 5cm during one strobe interval and the strobe is set to 20% faster, the ripples only move 4cm forward, creating an illusion of backward movement. This phenomenon is attributed to the brain's perception of motion based on the last observed position of the ripples, leading to a visual misinterpretation.

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nazz
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Stoboscopic effect and why!

if the frequency of the strobe is higher than the frequency of the water ripples then the ripples will appear to move slowly backwards.

can some one expain with formula's or with some technical trems why this happens?

i know if the strobe has higher frequency than the ripples will look as if they are moving backward because of the difference in f, but i need a more convincing explanation
 
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Welcome to pf
It's an optical (really a visual) illusion.
Remember you can't identify individual ripples uniquely - they all look the same.

Suppose the ripples move forward 5cm in one strobe interval
If you set the strobe 20% faster then they will only have had time to move forward 4cm.
When you look at them the nearest ripple to where you eye remembered the last position is now 1cm behind it - so you brain thinks the ripple moved back 1cm.

It's the same effect used for moving christmass tree or highway diversion lights.
 
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thanks for the clarification, gret help
 

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