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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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Because an engineer tested this and found the correct water pressure to lift the sphere just a little bit on the water. And the craftsmanship needs to be spot on. No dents or big imperfections on the sphere, a perfect fit with equal water dispersal on the pedestal.
It can happen to cars too when rain water accumulates on the road. If they go fast enough the tires lose contact with the ground and the car will become unsteerable.
We had one at the campus of my last job that was carved with a globe. You could grab onto it and spin it around if you could get enough friction.
Orbs were pondered.
The house pressure is between 50 and 100psi. Pounds per square inch. So now figure out how many pounds your ball weighs. Then divide that number by the pressure you have. This gives you the area you need. Make it slightly larger by 10%. Then figure out the radius of the circle you need to make that area. Cut that circle into the bottom part. Super easy, you just need a CNC grinding machine. Now take the ball that was also made by the CNC magic machine and lif it over the hole. You'll need like a hundred buddies for that. Apply the pressure to the water and viola! The sphere floats! But as it floats, the water escapes thru the sides so it can't fly away, it can only float. To make the water come out at some crazy pressure just make the circle a little smaller and increase your pressure. The smaller the circle, the more pressure you'll need. It's totally possible to have a ball that floats and sprays everyone around. You just have to overcome the boundary layer pressure. The speed of any liquid near a wall is 0. So the liquid right next to the wall is what can move. This motion crates a boundary layer where the speed of the liquid goes from 0 at the wall to some larger amount. A small gap means you'll never hit the full speed of your pump. A big gap means your pump can develop a full speed flow. So in short, big pump, small ball, big circle ⭕🔴 will get you a flying ball that splashes everyone and a big electric and water bill.
How does the whole surface of the marble stay wet when the water comes out the bottom? Surface tension and chaotic motion causing the marble to spin every which way?
Yes, I've seen some of those marbles that haven't spinned for a while and top of it is dry.
Yes. But if you stop one by grabbing it the top half will indeed dry off, and even fairly quickly if you do it on a hot summer day in the sun.
Water squirts out under pressure from the tires
Here's some advice - when people take the time and effort to answer the question you asked, don't immediately accuse them of being wrong about the thing you already said you don't understand. It's foolish and a just a dick move in response to people going out of their way to help you.
not quite unfortunately https://en.wikipedia.org/wiki/Aquaplaning
One day, you could be in for an unpleasant surprise. This is why you should slow down when it rains.
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.