Alert Diver Misstatement

[Groundhog246]

Ooops. Good job I don't trade in gold isn't it.

 

[cornfed]

Never mind...

 

[Rick Murchison]

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

The lake level would go up by about 10/11 the volume of the lead weight.
As for the second part, which ounces are you using?
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As long as we're thinking about such things, consider a glass of water with an ice cube floating in it. As the ice cube melts, what happens to the level of the water in the glass?
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If I have a glass with 100ml of pure water in it and I add 100ml pure ethanol, how much (in ml) alcohol/water mixture will I end up with?
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ok... that's enough for now.
Rick

 

[roakey]

The lake level would go up by about 10/11 the volume of the lead weight.

No, groundhog had it, while in the boat the lead displaces its WEIGHT of water, which is greater than the lead's volume. So when it's pitched into the water, it now only displaces its volume, so the lake level goes down (less water being displaced).

Back to the article, I've got to find my AD, this is obviously the article I scanned and put down when they went to great lengths on how to address roll (a rare problem with divers) and completely ignored pitch (a ubiquitous problem with divers), just like the rest of the industry...

Roak

 

[dc4bs]

The lake level would go up by about 10/11 the volume of the lead weight.
As for the second part, which ounces are you using?
-----
As long as we're thinking about such things, consider a glass of water with an ice cube floating in it. As the ice cube melts, what happens to the level of the water in the glass?
-----
If I have a glass with 100ml of pure water in it and I add 100ml pure ethanol, how much (in ml) alcohol/water mixture will I end up with?
-----
ok... that's enough for now.
Rick

One would think that as the ice melts the water level goes down. Ice (made from water) takes up more volume than water (as a liquid). Therefore it's positively bouyant in liquid water. BUT, some of the ice ends up being pushed out of the water due to this bouyancy... As that melts back down into the water, it cancels out the water level drop. Hmmm. Not 100% sure on this though. Good question.

The MAIN reason the water level goes down is evaporation while waiting for the ice to melt... (a relative humidity dependant variable and presumably ignored for this exercise)

Mixing water and ethanol: you'll end up with less than 200ml of liquid since the water and ethanol molecules "fit" together with each other better than they do with others of their own kind. I'm not sure how much less than 200ml though. It's been a long time since high school chemistry and I never liked it much anyway. Conversely, you can add a certain amount of ethanol to water without changing the volume at all. Kind of like adding some water to a full bucket of sand or gravel. It "fills in the gaps".

I LIKE the lead thrown out of the boat question. I'll have to remember that one for next time I DM...

 

[fgray1]

Who cares. Go dive and have fun doing it.

Fred

 

[Groundhog246]

I don't think ice melting changes the level at all. Water expands when frozen (that's why ice floats). In the glass it displaces a volume equal to it's weight. As it melts it volume is reduced to that of it's liquid state. The weight of water remains the same. (this is fun)

 

[Rick Murchison]

No, groundhog had it, while in the boat the lead displaces its WEIGHT of water, which is greater than the lead's volume. So when it's pitched into the water, it now only displaces its volume, so the lake level goes down (less water being displaced).

Yeah, yeah, yeah... down by 10/11 the volume of the lead... my little pea brain was taking the lead out of the water and putting it in the boat.
Rick

 

[Rick Murchison]

Mixing water and ethanol: you'll end up with less than 200ml of liquid since the water and ethanol molecules "fit" together with each other better than they do with others of their own kind. I'm not sure how much less than 200ml though. It's been a long time since high school chemistry and I never liked it much anyway. Conversely, you can add a certain amount of ethanol to water without changing the volume at all. Kind of like adding some water to a full bucket of sand or gravel. It "fills in the gaps".

Well done!
A small point, though, and one to really twist your brain... you can add a small amount of water to pure ethanol (up to about 4%) without changing the total volume, but you can't add any ethanol to pure water without changing the volume.
Why?
Rick

 

[Rick Murchison]

I don't think ice melting changes the level at all. Water expands when frozen (that's why ice floats). In the glass it displaces a volume equal to it's weight. As it melts it volume is reduced to that of it's liquid state. The weight of water remains the same. (this is fun)

Right on the money!
You get an "A" for the day!
Rick