# Lifting power at the bottom of the ocean?

#### CS_SJ

Hello,

I'm a little confused about water pressure at extreme depths. Let's say that you attached a 100 lb. weight to a barrel, and the barrel had enough barely enough buoyancy to be able to just hold that weight at the surface (see Figure 1.)

Then, you took the same barrel (a strong barrel that won't compress) and you put it at the bottom of the ocean 1000 feet down (see Figure 2) would the pressure down there give the barrel more lifting power? Would that same barrel be able to lift 1000 lbs. down there? 2000 lbs.?

Or, would the pressure on top of the barrel equal it all out and even 1000 feet down, all the barrel could lift is 100 lbs.?

Extra question: if the barrel at the bottom of the ocean WOULD have more lifting power, does that mean it would accelerate like a rocket off of the bottom of the ocean, and then slow down the closer it got to the surface?

Thank you,

- DJ

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#### Hayseed

The "lifting power" is called the buoyancy. That force is proportional to the pressure difference, between the top of the object and the bottom of the object. No matter how deep.

This is a completely different scenario, than the water in a cave scenario. All the little details make a big difference.

In the sealed tank setup, the volume of the object does not change. It will have the same buoyancy no matter how deep. But a balloon is different. As the balloon is pulled deep, it shrinks. Because the water pressure can compress the air in balloon, the balloon gets smaller. SO, the pressure difference is smaller as the balloon sinks. The lifting power decreases.
May I ask how old you are, and what is your background? Your two posted questions are completely different situations.

IF the sinking body, changes it's volume, then the buoyancy changes.

I believe you are confused, because you are comparing two different dynamics.

In the cave example, 1000 ft of water is in contact with the air bubble. In the sealed tank setup, the water is not in contact with the air inside the tank. Cave air can be compressed. The sealed tank air can not be compressed.

Does any of this make any sense to you?

CS_SJ

#### CS_SJ

The "lifting power" is called the buoyancy. That force is proportional to the pressure difference, between the top of the object and the bottom of the object. No matter how deep.

This is a completely different scenario, than the water in a cave scenario. All the little details make a big difference.

In the sealed tank setup, the volume of the object does not change. It will have the same buoyancy no matter how deep. But a balloon is different. As the balloon is pulled deep, it shrinks. Because the water pressure can compress the air in balloon, the balloon gets smaller. SO, the pressure difference is smaller as the balloon sinks. The lifting power decreases.
May I ask how old you are, and what is your background? Your two posted questions are completely different situations.

IF the sinking body, changes it's volume, then the buoyancy changes.

I believe you are confused, because you are comparing two different dynamics.

In the cave example, 1000 ft of water is in contact with the air bubble. In the sealed tank setup, the water is not in contact with the air inside the tank. Cave air can be compressed. The sealed tank air can not be compressed.

Does any of this make any sense to you?
Thank you! This helps a lot.

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