Tube Buoyancy Question: How Much Force Is Needed?

In summary: So the force required to pull the object through the water is 10 pounds plus the water pressure, or 10 pounds plus 8.3 pounds.
  • #1
jackrabbit
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Suppose you had a hollow tube, closed at both ends. The tube weighs 10 pounds and would float in water.

Suppose also there is an empty container with a hole at the bottom. The tube is stuck through the hole so that half of it is in the tank and half is sticking out the bottom. Assume a water tight fit between the tube and the hole.

Now, fill the tank with water so that the water surface is a foot or two above the top of the tube.

How much force is necessary to pull the tube through the water and completely into the container? (Assume for the sake of argument that there is no friction between the tube and the sides of the hole). Is it (a) 10 pounds; (b) 10 pounds plus water pressure; (c) something less than 10 pounds because the top half of the tube is buoyant even though the bottom half is sticking out the bottom of the hole; or (c) something else?
 
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  • #2
What do you think?
 
  • #3
I don't know. My gut says it should be the full 10 pounds plus water pressure, but I am having trouble figuring out why it wouldn't be less given the buoyancy of the top half (perhaps less than 10 pounds for the tube but then add water pressure?).
 
  • #4
jackrabbit said:
I don't know. My gut says it should be the full 10 pounds plus water pressure, but I am having trouble figuring out why it wouldn't be less given the buoyancy of the top half (perhaps less than 10 pounds for the tube but then add water pressure?).
Your gut is correct. Buoyant force is the net force on the body due to the pressure of the surrounding fluid. Under 'normal' circumstances, the body is completely surrounded by fluid or is floating, thus the buoyant force is upward. But in a case like you describe, the net force from the fluid actually pushes down on the object.
 
  • #5


The force needed to pull the tube through the water and into the container would be (b) 10 pounds plus water pressure. This is because the weight of the tube (10 pounds) is being counteracted by the buoyant force of the water on the top half of the tube, but the bottom half of the tube is still exposed to the water pressure pushing down on it. In order to completely submerge the tube into the container, an additional force equal to the water pressure on the bottom half of the tube would be needed. This force would vary depending on the depth of the water and the density of the water.
 

FAQ: Tube Buoyancy Question: How Much Force Is Needed?

1. What is tube buoyancy?

Tube buoyancy is the upward force exerted by a fluid, such as water, on an object that is partially or completely submerged in the fluid. This force is equal to the weight of the fluid that the object displaces.

2. How is tube buoyancy calculated?

To calculate tube buoyancy, you need to know the density of the fluid, the volume of the object, and the acceleration due to gravity. The formula for calculating buoyancy is: Buoyancy force = (fluid density) x (volume of object) x (acceleration due to gravity)

3. How much force is needed for a tube to float?

The amount of force needed for a tube to float depends on the weight of the tube, the density of the fluid, and the volume of the tube. The buoyancy force must be greater than or equal to the weight of the tube for it to float.

4. Can a tube ever sink due to buoyancy?

Yes, a tube can sink due to buoyancy if it is not fully submerged in the fluid or if the buoyancy force is not greater than the weight of the tube. Other factors such as shape and weight distribution can also affect the buoyancy of a tube.

5. What are some real-world applications of tube buoyancy?

Tube buoyancy has many practical applications, such as in boats and ships, where the shape and weight distribution of the hull allow it to stay afloat. It is also used in scuba diving equipment, life jackets, and submarines. Understanding buoyancy is also essential in designing and constructing bridges and other structures that must withstand the forces of water.

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