# Buoyancy of object on telescopic riser with only part of its bottom in water

• bchohertz
In summary, the buoyant force on the cube will be a fraction of the surface area on the bottom of the cube exposed to water, as the volume taken up by the telescopic cylinder is not available for water displacement. However, the buoyant force can also be calculated by considering the pressure gradient, which means that the force will increase with a smaller surface area.
bchohertz
If a cube submerged in water is attached to the floor with a telescopic cylinder taking up part of the surface area on the bottom of the cube, will the buoyant upward force be a fraction of the surface area on the bottom of the cube exposed to water, or will the full buoyancy effect take place, as long as at least a little of the bottom surface area of the cube is exposed.

Assume the cube is less dense than the water it is in.
Assume the telescopic cylinder does not create any tensive or vacuum force, and is ridgid. It is just preventing some of the water from contacting part of the bottom surface of the cube.

From what I have read on the forums, if the ENTIRE bottom of the cube is not in contact with water the cube will have NO buoyant uplift. My question is what if only part of the bottom surface of the cube is in contact with water? Do I calculate buoyant force normally and multiply by the fraction of bottom surface area that water comes in contact with? Or, does the entire normal Buoyant force get applied.

Buoyant force depends on displaced volume, not surface area. It won't change just because there's a cylinder attached (aside from any volume displaced by the cylinder).

bchohertz said:
If a cube submerged in water is attached to the floor with a telescopic cylinder taking up part of the surface area on the bottom of the cube, will the buoyant upward force be a fraction of the surface area on the bottom of the cube exposed to water, or will the full buoyancy effect take place, as long as at least a little of the bottom surface area of the cube is exposed.

I will refer to 'the basin' for the container of the body of water that the cube is floating in.

In a sense the cube you describe is not attached to the floor of the basin; your statement about the cilinder implies it exerts neither an upward nor a downward force. All that the cilinder does is prevent sideways motion.

We have that in order to float the cube must display its weight in water. It follows that the cube-with-cilinder will be immersed more deeply than the same cube without cilinder. The volume taken up by the cilinder is not available for water being displaced.

Alternatively, you can evaluate the buoyancy by considering pressure gradient. In a fluid like water there is a pressure gradient; the pressure increases linearly with depth. The bottom of the cube is below the surface, the pressure acting upon the bottom of the cube provides the required upward force for buoyancy. As you describe: with the cilinder in place there is less surface area available. Force is pressure times surface area. Less surface area means a larger pressure is required to obtain the same amount of force.

## What is buoyancy?

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

## How does the buoyancy of an object on a telescopic riser work?

The buoyancy of an object on a telescopic riser is dependent on the volume of water that the object displaces. The more water it displaces, the greater the buoyant force. Therefore, if only part of the bottom of the object is in the water, the buoyant force will be less than if the entire object were submerged.

## What factors affect the buoyancy of an object on a telescopic riser?

The main factors that affect the buoyancy of an object on a telescopic riser are the volume of water that the object displaces, the density of the object, and the density of the fluid (water). Other factors such as the shape and size of the object also play a role.

## How can the buoyancy of an object on a telescopic riser be calculated?

The buoyancy force on an object can be calculated using Archimedes' principle, which states that the buoyant force is equal to the weight of the fluid that the object displaces. The weight of the fluid can be calculated by multiplying the volume of fluid displaced by its density, and the buoyant force can then be compared to the weight of the object to determine if it will sink or float.

## What are some applications of understanding the buoyancy of an object on a telescopic riser?

Understanding the buoyancy of an object on a telescopic riser is important in many areas such as naval and marine engineering, offshore oil and gas operations, and shipbuilding. It is also used in designing and constructing structures such as bridges and dams, as well as in recreational activities such as scuba diving and boating.

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