Alert Diver Misstatement

[roakey]

Just to derail the discussion, one of the problem solving problems we used to throw out in interviews was "You're floating in the middle of a lake in a rowboat. You pick up a lead weight from the bottom of the boat and throw it into the water. Does the lake's level go up, down or remain the same?"

And the real tricky question (not asked in interviews): "Which weighs more, an ounce of gold or an ounce of hay?" Careful, this is actually a double trick question...

Roak

 

[donacheson]

DAN definitely needs some better editors. The author's other statements show that he does understand Archimedes law. I also suspect that the author knows that many tanks (mostly steel) are negative buoyant when empty, even though the article says

The chart with data on 65 and 80 cu ft. aluminum tanks is a bit weird too. It has 65 cu ft of air weighing 5.9 pounds, while 80 cu ft is 6 pounds. It also lists size and buoyancy info for the short, fat 8"dia x 23" tank rather than the more common 7.25" x 26" AL80.


picky, picky, picky..... but that's what they should have editors doing before it is printed.

Charlie

There are other errors in the article as well.

The table includes what are most likely erroneous dimensions for the tanks - every Al 80 I've encountered is 7.25 inches in diameter. However, the dimensions shouls have been left out since they're irrelevant to the discussion.

The author got it backwards when he wrote "An object with a specific gravity of more than 1.0 floats ... If less than 1.0, it sinks ..." One can get pickier about the use of specific gravity in this ca, but llet's not.

The article has divers breathing steel and aluminum as well as air during a dive: "The difference between a full tank and an empty one will vary according to the size AND MATERIAL {my caps} of the tank."

There's more, but that's enough. This is the second article Alert Diver has published about weighting divers. The first wasn't much better.

 

[saying]

A submerged diver (except while escending) ...

Which direction is escending?

 

[plsdiver4377]

By the way it's Monday so I could be wrong.

Just to derail the discussion, one of the problem solving problems we used to throw out in interviews was "You're floating in the middle of a lake in a rowboat. You pick up a lead weight from the bottom of the boat and throw it into the water. Does the lake's level go up, down or remain the same?"

And the real tricky question (not asked in interviews): "Which weighs more, an ounce of gold or an ounce of hay?" Careful, this is actually a double trick question...

Roak

Here goes.

Lake level goes up.

The ounce of hay weighs more than the ounce of gold. Troy versus Avoirdupois weight.

 

[roakey]

By the way it's Monday so I could be wrong.

Here goes.

Lake level goes up.

The ounce of hay weighs more than the ounce of gold. Troy versus Avoirdupois weight.

Nope, nope (but you saw through to the trick part of the question! )

Roak

 

[d33ps1x]

Snore....Hmm...Whaa...Oh. Sorry! I always used to fall asleep in physics class.

 

[plsdiver4377]

Snore....Hmm...Whaa...Oh. Sorry! I always used to fall asleep in physics class.

I did too since I missed them both :bonk: . I should stick to ground, grid, GPS questions they're easier on my little brain. By the way Roak post the answers sometime, inquiring minds want to know.

Cheers

 

[norcaldiver]

Just to play devil's advocate....
I looked up "mass" in the dictionary and got this: The physical volume or bulk of a solid body. The mass of an object is not dependent on gravity and therefore is different from but proportional to its weight.
So volume is mass, but just to make sure I looked it up in the thresaurus and found this: Synonyms:...volume

Oh and it's "Archimedes' principle, not law, and the principle states: Any object wholly or partially immersed in a fluid is buoyed up by a force equal to the weight of the fluid displaced by the object"

 

[Groundhog246]

Just to derail the discussion, one of the problem solving problems we used to throw out in interviews was "You're floating in the middle of a lake in a rowboat. You pick up a lead weight from the bottom of the boat and throw it into the water. Does the lake's level go up, down or remain the same?"

Down (I wouldn't want to try and measure by how much). In the boat the lead displaces it's own weight of water and is floating. Dropped in the lake it is displacing it's own volume but less than it's weight, thus it sinks and the lake level goes down. (I have an unfair advantage as I own a sail boat with a big chunk of metal bolted to the bottom and understand the term "displacement". Further info can be found here )

And the real tricky question (not asked in interviews): "Which weighs more, an ounce of gold or an ounce of hay?" Careful, this is actually a double trick question...

Roak

Gold is measured in Troy ounces and 1 troy ounce = 1.097 ordinary ounce so an ounce of hay weighs more.

 

[roakey]

Down (I wouldn't want to try and measure by how much). In the boat the lead displaces it's own weight of water and is floating. Dropped in the lake it is displacing it's own volume but less than it's weight, thus it sinks and the lake level goes down.

Yup!

Gold is measured in Troy ounces and 1 troy ounce = 1.097 ordinary ounce so an ounce of hay weighs more.

Ouch. Yes, no. If gold weighs 1.097 normal ozs, gold weighs more...

Roak