Theoretical Question about Buoyancy

In summary, the conversation discusses the concept of buoyancy and its application to a frictionless box at the bottom of a lake. The question arises as to whether a buoyant force exists in this scenario, and if it goes against Archimedes' principle. Various scenarios are explored, including the possibility of removing all water from underneath the box, but it is concluded that there will always be some form of matter present, therefore still adhering to Archimedes' principle. A separate experiment involving a ping-pong ball and water is also mentioned.
  • #1
conkermaniac
11
0
This is a question that's been bothering me for a while. Archimedes's principle states that the weight of the water displaced is equal to the buoyant force. If a frictionless box sinks to the bottom of a lake, does it feel a buoyant force? Buoyancy exists because of a difference in pressure between the top and the bottom of the box. If the box is already at the bottom, then there can be no water underneath the box, and consequently no pressure exists underneath the box. If this is so, then does a buoyant force NOT exist? Doesn't this go against Archimedes' principle, which to the best of my knowledge does not contain any exceptions? :confused:

Thanks for your help! :)
 
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  • #2
If you could remove all water from underneath the box, and there was no water below it, and there was no way water could slip under it (be pressed under it by pressure) and there was no water or air in the ground under it... well, there might be a case where Archimede's principle did not apply. Maybe there is something I'm missing...

But it doesen't matter, because you will never remove all the free matter from under it. There will always be water under it, or the water can be squeezed under it, or there is water in the ground etc...
 
  • #3
I've been informed of a certain ping-pong ball experiment, where you put a ping-pong ball into an upside-down container that's been cut open at the other end. If you then pour water on top of the ping-pong ball, the ping-pong ball will stay at the bottom.
 

1. What is buoyancy?

Buoyancy is the upward force exerted by a fluid (such as water) on an object that is partially or completely submerged in it. This force is equal to the weight of the fluid that the object displaces.

2. How is buoyancy calculated?

Buoyancy is calculated using Archimedes' principle, which states that the buoyant force is equal to the weight of the fluid that the object displaces. This can be represented by the equation Fb = ρVg, where Fb is the buoyant force, ρ is the density of the fluid, V is the volume of the fluid displaced, and g is the acceleration due to gravity.

3. What factors affect buoyancy?

The buoyant force on an object is affected by the density of the fluid, the volume of the fluid displaced, and the acceleration due to gravity. The shape and size of the object can also affect the buoyant force, as well as the pressure and temperature of the fluid.

4. Can an object sink if it is buoyant?

Yes, an object can sink even if it is buoyant. This can happen if the weight of the object is greater than the buoyant force exerted by the fluid. In this case, the object will sink until it reaches a depth where the buoyant force and the weight of the object are balanced.

5. How does buoyancy affect floating objects?

Buoyancy is what allows objects to float on the surface of a fluid. The buoyant force pushes up on the object, while the weight of the object pushes down. If the buoyant force is greater than the weight of the object, it will float. If the weight of the object is greater, it will sink. The shape and density of the object also play a role in whether it will float or sink.

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