mjcoon
Well-known member
Do you really believe your special version of hydrostatics, or are you countering the idea that people can learn from reading this forum?
How much does my 40Kg anchor weigh when in sea water?
- Thread starter tudorsailor
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Bouba
Well-known member
That’s a bit harsh…there is weight and mass…the question was weight…weight is gravity…to discount the weight of a substance on top of the anchor is like you going and standing on your bathroom scales and then saying, how much would I weight without my head
Alan S
Well-known member
Come on, Bouba, you're winding us up.
I know you are.
What about dombuckley's submarine in post 32?
Bouba
Well-known member
If I stood on my bathroom scales...and a strong wind blew over my head (the kind that blows roofs off)..my scales would show that I weight less than I would on a calm day...because air pressure affects my weight.Come on, Bouba, you're winding us up.
I know you are.
What about dombuckley's submarine in post 32?
If I stood on my bathroom scales and it was raining... I might weigh more because of the weight of water on my skin
Bouba
Well-known member
Now... my mass may not change...I still possess the same amount of substance in the same amount of volume
KevinV
Well-known member
Please tell me you're just testing our ability to explain
The water under the anchor is pushing up with (pretty much) the same force as the water above is pushing down - likewise in air.
Bouba
Well-known member
(I’m writing this as I eat my dinner)...your weight is very variable...even my (very expensive) scales add half a kilo to my weight because I live in France (or is it takeaway 
).. I can go up a mountain or another country and my weight will change
).. I can go up a mountain or another country and my weight will change
Bouba
Well-known member
This is a red herring...pressure increases as you descend....otherwise it would only change once you are on the sea bedPlease tell me you're just testing our ability to explain
The water under the anchor is pushing up with (pretty much) the same force as the water above is pushing down - likewise in air.
Bouba
Well-known member
If you put a set of bathroom scales on the ocean floor...would they read zero...or the weight of the water above?..if the answer is the weight of water...what if you put a set of scales in the exact silhouette as your anchor...would only the weight of the anchor register?
KevinV
Well-known member
Yes!
Daydream believer
Well-known member
Are you sure that you need a 40Kg anchor in the first place?
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Bouba
Well-known member
If you waterproofed them, they should only read the weight above
dombuckley
Well-known member
I suggest you dont go diving into a swimming pool then. Cause (assuming you're about 1.8m tall and about 60cm across the shoulders), if you reach about 1m down, you'll be slammed down into the bottom of the pool by about a ton of water pressing down on you. But dont worry, all you have to do is stop swimming and come upright in the water, then you'll only have about 200kg pushing you down. Easy.
Go for a swim. I bet you wont notice any difference, and you certainly wont be crushed by a ton of water above you while you sit in the shallow end.
KevinV
Well-known member
If you *sealed* them they would measure the weight of the water above - and read exactly the same if you held them upside down or sideways
Bouba
Well-known member
Excellent...so an anchor shaped waterproof bathroom scales on the ocean floor will measure the weight of the anchor and the anchor shaped column of water above
capnsensible
Well-known member
Regarding sea water density:
The range of density in the oceans is from about 1.020 to 1.070 g/cm3 The changes in density are caused mainly by variations in pressure, salinity and temperature:
· colder water more dense
· saltier water more dense
· higher pressure causes density increase - pressure increases with depth due to the mass of water above
The range of density in the oceans is from about 1.020 to 1.070 g/cm3 The changes in density are caused mainly by variations in pressure, salinity and temperature:
· colder water more dense
· saltier water more dense
· higher pressure causes density increase - pressure increases with depth due to the mass of water above
capnsensible
Well-known member
Regarding submarines.
Military submarines have internal tanks so that a compensation can be made for changes in depth.
As a submarine goes deeper, it's mass is reduced by water pressure. Thus the weight exceeds the mass.....in simple terms. So as that change of depth happens, ballast water is pumped from those tanks to sea.
As the submarine rises, water is flooded back I to the internal tanks to compensate for sea water pressure falling.,
The aim is to keep the submarine at neutral buoyancy whatever the depth. Some positive or negative buoyancy can be overcome by propulsion. So, for example, if the submarine is 'heavy' when going deep, more revs will do the job until sufficient water is pumped out.
Military submarines have internal tanks so that a compensation can be made for changes in depth.
As a submarine goes deeper, it's mass is reduced by water pressure. Thus the weight exceeds the mass.....in simple terms. So as that change of depth happens, ballast water is pumped from those tanks to sea.
As the submarine rises, water is flooded back I to the internal tanks to compensate for sea water pressure falling.,
The aim is to keep the submarine at neutral buoyancy whatever the depth. Some positive or negative buoyancy can be overcome by propulsion. So, for example, if the submarine is 'heavy' when going deep, more revs will do the job until sufficient water is pumped out.
capnsensible
Well-known member
And they got anchors..... 
Bouba
Well-known member
I never thought about that....how much do they weigh?And they got anchors.....
KevinV
Well-known member
Dude, you really need to learn some basic physics - think of old-fashioned, spring scales - no seals, just a flat plate attached to a spring and a dial that moves if a weight is applied.
Now put those scales in water of any depth. They will read zero, because the water under the plate is pushing up as hard as the water over the plate is pushing down. There is no force to move the plate.
None of the parts have magically become heavier either - they are the same parts, consisting of the same number of atoms.