Buoyancy of a pail of water problem

In summary, when a hung object is submerged in water, the weight of the pail with water increases due to the buoyant force acting on the object. The tension in the string changes since there is now a buoyant force acting on the object. The weight added will be equal to the weight of the object when it is in air. If water spills, the weight added will be equal to the buoyant force on the submerged object.
  • #1
darkmagic
164
0
I have a question, if a hung object is submerged in a pail of water, does the weight of the pail with water increase. The object is still hung and no water spills.
 
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  • #2


What do you think?
 
  • #3


Well, I think it does not add. Since the object is hung? Am I correct?
 
  • #4


darkmagic said:
Well, I think it does not add. Since the object is hung? Am I correct?
No. Ask yourself: Before the object is in the water, what's the tension in the string? Does that tension change when the object is submerged?
 
  • #5


before, the tension is the weight of the object. when submerged, the tension change since there is a bouyant force that acts on the object. Am I correct?
 
  • #6


darkmagic said:
before, the tension is the weight of the object. when submerged, the tension change since there is a bouyant force that acts on the object. Am I correct?
Exactly.

And if the water exerts a buoyant force on the object, the object must exert an equal and opposite force on the water. (Newton's 3rd law.) So the water is being pushed down by the object.
 
  • #7


So it adds weight. The weight added will be the weight of the object when in air, since buoyant force will be cancelled?
 
  • #8


darkmagic said:
So it adds weight.
Yes.
The weight added will be the weight of the object when in air, since buoyant force will be cancelled?
No. The buoyant force isn't cancelled. But a force equal to the buoyant force will be added to the 'weight' of the pail plus water.
 
  • #9


So buoyant force will be added? I got it. How about if water spills? The spilled water will be the buoyant force that will be out of the pail. However, the object exerts a force equal but opposite of the buoyant force, so it adds weight? correct?
 
  • #10


darkmagic said:
So buoyant force will be added? I got it. How about if water spills? The spilled water will be the buoyant force that will be out of the pail. However, the object exerts a force equal but opposite of the buoyant force, so it adds weight? correct?
If the pail starts out full to the brim, then the weight of the spilled water will exactly equal the buoyant force on the submerged object. (See Archimedes' principle.)
 
  • #11


Ok. I got it now. Thanks a lot.
 

1. What is the concept of buoyancy?

Buoyancy is the upward force exerted by a fluid 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 does the shape of the object affect its buoyancy?

The shape of an object affects its buoyancy because it determines the amount of fluid that it displaces. Objects with larger volumes will displace more fluid and therefore experience a greater buoyant force.

3. What is the relationship between the density of an object and its buoyancy?

The density of an object is directly related to its buoyancy. Objects with a higher density than the fluid they are submerged in will sink, while objects with a lower density will float. The buoyant force acts in the opposite direction of the object's weight.

4. How does the depth of the object in the fluid affect its buoyancy?

The depth of an object in a fluid does not affect its buoyancy. As long as the object is submerged, the buoyant force will remain the same. However, the pressure exerted by the fluid on the object will increase with depth, which may affect other factors such as the object's shape or density.

5. Can an object have negative buoyancy?

Yes, an object can have negative buoyancy if its density is greater than that of the fluid it is submerged in. In this case, the buoyant force will be less than the object's weight, causing it to sink.

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