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Is it Tuesday? Buoyancy

2big bronco

2big bronco

Og irate
Joined
May 19, 2020
Member Number
188
Messages
4,274
Loc
Prunedale ca
Does volume of water affect how floatable something is? Would a ping pong ball resist being pushed down more in a bucket of water vs a glass of water?
 
Does not matter the amount of water would be the same in 1 gallon or a million.
 
As long as there is enough water to be displaced the buoyancy is static since it depends on the volume of the floating vessel.
 
until you get into small enough quantities that the surface tension of the water comes into play, the excess quantity doesn't matter :rasta:
 
DWT said:
As long as there is enough water to be displaced the buoyancy is static since it depends on the volume of the floating vessel.
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I understand what you are saying but cant wrap my head around the idea of more water surrounding something not creating more force trying to push it's way under.

Does a 100' tall damn have the same force on it if its retaining a pond 100' deep vs a huge lake 100' deep?
 
2big bronco said:
I understand what you are saying but cant wrap my head around the idea of more water surrounding something not creating more force trying to push it's way under.

Does a 100' tall damn have the same force on it if its retaining a pond 100' deep vs a huge lake 100' deep?
Click to expand...

That isn't buoyancy anymore, but yeah I'd imagine they would both have the same pressures on them as long as they are both 100' deep. BTW a 100' pond would still be huge. The differences would be how wide of an opening they are trying to Dam up. As that gap got wider the thickness and strength of the dam would have to go way up.

Think of a 1/2' air line at 100 psi. You can put your finger over it and stop that pressure because the area is small. PiR^2 would be (3.14*.250^2)*100psi = 19.6lbs of force you would have to put against the end of that hose to stop the pressure from coming out.

Now think of 100psi on a 4x8 sheet of plywood. 48"x96"x100psi= 460800lbs or 230.4 tons to hold that down with 100psi of force acting against it.
 
2big bronco said:
I understand what you are saying but cant wrap my head around the idea of more water surrounding something not creating more force trying to push it's way under.

Does a 100' tall damn have the same force on it if its retaining a pond 100' deep vs a huge lake 100' deep?
Click to expand...

100' is 100' no matter if in a pond or ocean even if it's on a treadmill it's the same.
 
2big bronco said:
I understand what you are saying but cant wrap my head around the idea of more water surrounding something not creating more force trying to push it's way under.

Does a 100' tall damn have the same force on it if its retaining a pond 100' deep vs a huge lake 100' deep?
Click to expand...

you are forgetting how gravity works, water is heavier than air, so it isn't pushing "out" in all directions like helium in a balloon :flipoff2:
 
Depth of water is what they call "head pressure" 100' deep water will have roughly 41 psi at the bottom, no matter how wide the birth. While having 0 psi at the top. Head pressure is about .41 psi per foot.

Buoyancy has nothing to do with depth of water, and is determined by the object, as it is what has Buoyancy.
 
As long as the area of contact between the object and the water surface does not change then it doesn't matter and the plane takes off.

Credentials: I passed science class on the second try.
 
So this all came about because I am trying to use water to assist in floating my septic tank out of the ground. Obviously water all the way around would be a lot better but I am trying to avoid digging in the 2 ft gap between the tank and my garage.

I was just trying to imagine digging 1' all the way around it vs more and how it would effect the "lift"

20201115_101436.jpg


20201115_103810.jpg
 
The three factors to consider in that scenario are solids left in the tank, overburden still on the tank, and corrugated tank grip on the underburrden. Otherwise there is nothing beyond the delta between water volume displaced by lighter than water mass. That tank could be an island in a ocean, or everything in a swimming pool and the only equation is weight vs water mass.
 
We dug out two 1000 gallon propane tanks with the tiniest mini-ex Home Depot had.

Once you get past the midpoint all the way around just lift that bitch out. We used a crane on a propane service truck.

If it’s wet the bottom of the tank takes some yanking on one end at a time to release it.

Forklift would work fine also.

Pretty sure you have 8 different pieces of equipment on hand to do just that.
 
Etyler2 said:
We dug out two 1000 gallon propane tanks with the tiniest mini-ex Home Depot had.

Once you get past the midpoint all the way around just lift that bitch out. We used a crane on a propane service truck.

If it’s wet the bottom of the tank takes some yanking on one end at a time to release it.

Forklift would work fine also.

Pretty sure you have 8 different pieces of equipment on hand to do just that.
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I already got it out, it wasnt to bad. Just put a strap in one lid opening and out the other and got up on it. It look a little while for the seal/suction/whatever to break it free and the water definitely helped
 
2big bronco said:
Does volume of water affect how floatable something is? Would a ping pong ball resist being pushed down more in a bucket of water vs a glass of water?
Click to expand...

Depends on the salt content in glass / bucket.
But a glass of water is small. Tiny, and I mean very tiny effects between the water and the glass side may introduce nano effects.

But generally, no.
 
2big bronco said:
I understand what you are saying but cant wrap my head around the idea of more water surrounding something not creating more force trying to push it's way under.
Click to expand...

Maybe it's offset by the water that has to "climb" around it?
Ball in a cup means the water around it has to climb quite a bit up the inside of the cup.
Ball in bucket means the water doesn't climb as much up the sides.

Maybe?
 
2big bronco said:
Does volume of water affect how floatable something is? Would a ping pong ball resist being pushed down more in a bucket of water vs a glass of water?
Click to expand...

It makes a TINY difference because the water the container the floating object is in will rise a little bit as some of the water is displaced by the volume of the object below the surface.
 
Oh boy! When do we get to planes and treadmills!:flipoff2:
 
The only thing that affects buoyancy is salt content or ground underneath. Saltwater is 1.025 fresh is 1 . If u take the same object floating in salt and put it in fresh it will sink at that ratio to fresh. Brackish water is whatever the difference is and the black sea has more salt.. otherwise archeymedis principles don't care about volume unless u hit ground on the bow stern or keel. Or that there is that little room in your container that the force of pushing it down displaces water
 
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2big bronco said:
I already got it out, it wasnt to bad. Just put a strap in one lid opening and out the other and got up on it. It look a little while for the seal/suction/whatever to break it free and the water definitely helped
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poopy strap is always the first to be borrowed out

how'd you convince the kid to thread the strap through?
 
[486 said:
;n198710]

poopy strap is always the first to be borrowed out

how'd you convince the kid to thread the strap through?
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I climbed in there myself. I pumped it months ago and left the kids loose so it wasnt to bad
 
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