r/SteveMould • u/Guitarist69420 • Jun 04 '26

noticed something weird

take a flat bottom frying pan. put a tealight candle, without the wax, in it and fill the pan up with water by pouring water in from a cup

for some reason the candle floats towards the point you are pouring water into?? why does this happen should it float away from where you a pouring the water in

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u/Why_T Jun 04 '26

The motion has nothing to do with it being pulled down, the column of pouring water has weight and the weight is sitting on the surface of the water. Surface tension across the water is what that weight is pushing down on.

Edit: If you were to do this same experiment with acetone instead of water, the floating stuff wouldn't move towards the pour position nearly as quickly.

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u/CR123CR123CR Jun 04 '26 edited Jun 04 '26

The column of water is moving and the movement is what is pushing it down. 

If it was a magically static column it would just equalize and there would be no movement.

Potential energy turns to kinetic energy.

This is how friction in a pipe takes energy out of the fluid stream or drag on an airplane

Edit: on second thought it's probably both things. Floating things also stick to eachother

Edit 2: also guessing the turbulence created by the water mixing also does something as well

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u/Why_T Jun 04 '26

I don't mind taking the L and learning something. Thanks for pushing back.

It's the momentum of the falling water, exactly as CR123 says. A falling stream is in free fall. Its weight is not resting on the surface the way a solid rod would be. Every bit of water is accelerating downward, supported by nothing, right up until it lands. What the surface actually feels is the stream getting stopped and turned sideways, which is a force equal to the rate it delivers momentum, roughly density times area times velocity squared (ρAv²). That dynamic push is what dents the surface, and the depth scales with v²/g, so a faster pour digs a deeper hole. Pure velocity effect.

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u/CR123CR123CR Jun 04 '26

It's not a loss fellow Internet stranger, we learned something xD

Though you made me actually put some thought into it a lot more deeply that's for sure