Water as weight rather than lead?

[MikeFerrara]

The abc's of diving.

A is for Archemedies (sp?)

Any way we don't care about how much our weights weigh. What we're interested in is their buoyancy.

Buoyancy = (weight of the water displace by an objet) - the weight of the object.

The buoyancy of water in water will be close to zero so all it would do is add drag.

 

[TwoTanks]

the question:

can you use water as weight, instead of lead weight?

No

For example, say that you take containers of water instead of lead. Yes, water weights six pounds per gallon, so you would have to take two gallons of water to equal 12 pounds, but...

Say you tie two milk gallons full of water to your waist...

Wouldn’t it be the same as wearing lead weights?

The out of water weight may be the same but in water your jugs would displace much more than the same weight of lead would, and therefore would have less negative buoyancy. Think about using 12 pounds of pine (wood). out of water it would weigh the same as the lead, but in the water the pine would float.
In buoyancy its not just weight, it is the density of the weight material.

We were having this discussion, and someone was saying that wouldn’t work, because the water would “float on water."

is this correct?

yes, a gallon of fresh water weighs less than a gallon of salt water, so if the container was neutral, the fresh water would float in the salt water. (by about 0.5 lb per cubic foot.) In other words it would take about half a pound of lead to sink a cubic foot of frest water in salt water)

Note: I don't know the exact densities of sea and fresh water off hand, so please excuse me if fresh water is not exactly 1/2 pound lighter than salt water.

As a sidenote, the deep sea explorer trieste, in 1960 used a large tank gasoline (or kerosine) for buoyancy because it was buoyant in water and wouldn't compress even at 35,000 feet.

TT

 

[RIDIVER501]

As a sidenote, the deep sea explorer trieste, in 1960 used a large tank gasoline (or kerosine) for buoyancy because it was buoyant in water and wouldn't compress even at 35,000 feet.

TT

Exactly liquids are incompressible, but remember boys and girls not all liquids are less dense then water

 

[Soggy]

In case the previous explanations don't help you understand....

An object is negatively buoyant if it weighs more than the volume of water it displaces and conversely, it is positively buoyant if it weighs less than that volume of water.

A liter of fresh water, for example, weighs 1 kg and takes up a cubic decimeter (10cm x 10cm x 10cm). If you have an object with those dimensions that weighs 2 kg, it will sink and be 1kg negatively buoyant. If you have an object of that size that weighs .5 kg, it will float and be .5 kg buoyant.

If you did a salt water dive and filled those jugs with fresh water....you'd actually be providing buoyancy, since fresh water is less dense.

 

[yknot]

What really confuses things is that submarines take on water in order to become less bouyant and therefore "dive". You could always wear doubles but keep one tank full of water instead of air. Really, if water caused negative bouyancy, we would all have light weight collapsible plastic weight bags we would add water to once we reached a dive destination or they would be built into our BC's.

 

[mccabejc]

Let's not be too hasty here. I think the original poster may have been referring to using "Heavy water" as a substitute for lead weights. In that case, it certainly would be heavier than water. Approximately 10% heavier, in fact. Added benefit is that if you are diving near a nuclear plant you are automatically protected from radiation, since "heavy water" is also a moderator of nuclear fission. The price, however, might be a tad higher than lead weights. Hydrogen sulfide separators are kinda pricey.

Mr. Science.

 

[Paul Evans]

Just to really stir things up

How much fresh water would you need when diving in a saltwater enviroment, assume the container is neutral in salt water :06:

 

[Afraid_of_Fish]

I'm not great with physics

Clearly.

can you use water as weight, instead of lead weight?

No. Just curious, but how did this even come up?

 

[Soggy]

Just to really stir things up

How much fresh water would you need when diving in a saltwater enviroment, assume the container is neutral in salt water :06:

Fresh Water will make you positively buoyant in a salt water environment. No amount of fresh water will let you sink.

 

[android]

Witches, ducks and wood float.
To determine if an object will be useful as ballast, it must be heavier than a duck.
Get a really big balance scale. Put a witch or a duck on one side and your ballast on the other side.