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marble balls floating on water are nice sculptures. why doesn't the water squirt out like when you pinch a garden hose ?
(lemmy.world)
this post was submitted on 12 Jul 2026
130 points (87.8% liked)
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It's a balancing act.
Water is not compressable, unlike air. When you put pressure behind the water, in the case of the marble ball, it simply moves the ball up out of the way. As the above comment says, it needs to be a very smooth matched set, both the ball and the pedestal have to match curves. This way the water is forced out evenly all the way around. Since you don't NEED the water to be super duper pressurized, the water doesn't spray out.
Here's one way of thinking about it: my pressure washer is 3000psi. When I put the nozzles on it, they spray super hard. If I take the nozzle off, that same water is merely flopping out of the end, looking like normal water out of a faucet. However, the more you constrict the opening, the more "spray-like" things get. The marble ball is the pressure washer without the nozzle. The water just flops out. But the more you force the opening to constrict, in this case by putting more and more weight on the ball to keep it from moving, then you will begin to see spraying, coming from the path of least resistance, likely an imperfection in the marble surface.
As for driving, Water splashes out from under the tires when you're going slow enough.
Speed up, thus increasing the forces acting on everything, and the water really doesn't like you being there.
If you take a garden hose and put your finger over the end, yes at full pressure water sprays everywhere.
Reduce the pressure both on your finger and in the hose, and the water no longer sprays out, it simply pushes your finger out of the way.
But that's why I'm askingbwhy the heavy marble ball doesn't force the water to spray out.
A light foam Ball would be like you described.
A heavy marble or granite ball will constrict the water forcing it out under pressure
This is "1kg of feathers vs 1kg of stone"
The weight of the ball is irrelevant if you have just enough pressure to lift it. When you add MORE weight to the marble ball, you will get the spray effect.
From what I understand, the water would spray out if it could, but there's not enough room, so the force instead pushes the ball up to give more room, but the engineer tailored the forces just right so that once the ball is lifted, the force that would have made the water spray out is already used up, so it doesn't spray. There's only enough force to spray or lift, not both.
Imagine a trickle of water. A heavy marble ball might construct it and force it to spray out, but a foam ball of the same size would not be heavy enough, and the water would push it up and out of the way.
So if your marble ball is forcing the water to spray out, increase the flow of water from a trickle up to whatever it needs to be for the water to lift the marble instead of spraying out.
(Is that right?)
Take your hose
Just barely turn it on.
Hold it up at eye level. The water fills the ending and slowly overflows the hose nozzle
Now take a marble slight bigger than the end of a hose and hold it tightly...water pressure will build and water will squirt out under pressure.
I don't see how the heavy granite balls don't do the same
The giant granite ball is not being held tightly. For your example just set the marble atop the opening of your hose. The water will continue to slowly overflow the end of the hose. Now if you exert additional force on the marble that's on you.
You should do this yourself and take a video. Share it and speculate with us why the objects in your video behave the way they do.
If you tried it with a bunch of different weights and sizes im sure you could get the same effect eventually.
An any hose and an any marble, not likely. This is a precision feat of engineering, with minds sharper than ours dedicated to the study and application of these forces.
If any monkey could do it then it wouldn't be impressive.
You can make a small model of this yourself using a marble and a dribbling hose. Try it.