How does buoyancy cause this wheel to spin?

In summary, the conversation discusses the behavior of a cylinder shaped wheel with an air pocket embedded near its edge when fully submerged in water. It is explained that the wheel is only free to spin about its center axis and that buoyancy is defined as an upward acting force caused by fluid pressure. However, it is noted that the fluid pressure does not cause the wheel to spin upward; rather, it is the unbalanced weight of the wheel. The solid side of the wheel weighs more than the side with the air pocket, thus causing it to turn. It is also mentioned that the wheel behaves the same whether it is fully submerged or not.
  • #1
RyanC83
2
0
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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  • #2
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.
 
  • #3
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!
 

1. How does the principle of buoyancy work in causing the wheel to spin?

Buoyancy is the upward force exerted by a fluid on an object immersed in it. When the wheel is placed in water, the water exerts an upward force on the wheel due to its weight and volume. This force causes the wheel to rotate as it tries to stay upright.

2. Why does the wheel spin when only partially submerged in water?

Even when partially submerged, the submerged part of the wheel experiences an upward force from the water, while the non-submerged part experiences a downward force from gravity. This imbalance of forces leads to the rotation of the wheel.

3. How does the shape and weight of the wheel affect its buoyancy and spinning motion?

The shape and weight of the wheel determine the amount of water displaced and the magnitude of the upward force acting on it. A lighter and more streamlined wheel will experience less resistance from the water, resulting in a faster spinning motion.

4. Can buoyancy be the sole cause of the wheel's spinning motion?

No, buoyancy alone cannot cause the wheel to spin. The wheel must also have a center of mass that is not aligned with its axis of rotation. This creates a torque, or a rotational force, that is responsible for the spinning motion.

5. Does the density of the fluid affect the buoyancy and spinning of the wheel?

Yes, the density of the fluid does affect the buoyancy and spinning of the wheel. A denser fluid will exert a greater upward force on the wheel, making it easier to rotate. This is why objects tend to float more easily in saltwater than in freshwater.

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