How does buoyancy cause this wheel to spin?

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SUMMARY

The discussion centers on the mechanics of buoyancy and its effect on a submerged cylinder-shaped wheel with an air pocket. The wheel, having the same density as water, experiences unbalanced weight due to the solid side being heavier than the side with the air pocket, causing it to spin rather than lift. Buoyancy does not influence the solid side, confirming that the wheel's behavior remains consistent whether submerged or not. The key takeaway is that the wheel's rotation is a result of weight distribution rather than buoyant forces.

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RyanC83
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Hi all,

In the attached image I have a cylinder shaped wheel with a air pocket embedded near its edge. The wheel has the same density as water and is fully submerged in a tank of water. Also the wheel is only free to spin about its center axis. If the wheel is rotated down the air pocket will cause the wheel to spin upward but how?

Buoyancy is defined as an upward acting force, caused by fluid pressure.

The wheel is under pressure from all side with a greater pressure from the bottom caused by gravity but I'm not understanding how fluid pressure can cause the wheel to spin upward?

If a ping pong ball is fully submerged in a tank of water the water is able to flow under the ball to give it lift. but in this wheel example the wheel is not lifting but spinning so water is not flowing at all.

Maybe someone could help me understand this a little better.

Thanks!
 

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RyanC83 said:
The wheel is under pressure from all side with a greater pressure from the bottom caused by gravity but I'm not understanding how fluid pressure can cause the wheel to spin upward?
It doesn't. What would cause the wheel to turn is its unbalanced weight: The solid side weighs more than the side with the air pocket.
 
Thanks Doc AI

That was the answer I was looking for. I assumed the solid side would have a neutral buoyancy (the wheel having the same density as water) but if buoyancy does not effect the side with the air pocket it will not effect the solid side ether. So the wheel behaves the same whether it is fully submerged underwater or not.

Thanks very much!
 

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