4 ms·

The foam can be high density and still be less dense than water. They would have to use foam that wasn't easily compressed or the structure would collapse from

by learc83 15y ago

The foam can be high density and still be less dense than water. They would have to use foam that wasn't easily compressed or the structure would collapse from the pressure. edit--I just checked, the type of foam used ranges from about 20 to 45 lbs/ft³. That qualifies as high density.

deleted 15y ago
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jholman 15y ago
Since I was curious about the relative densities, I looked it up and asked Google to convert to your archaic units. Water, at -30C, is around 60 lbs/ft³, so indeed the foam is denser. I was _going_ to claim that water is denser still, way down deep in the ocean. But I thought I'd check it out first, and although I'm not well-educated enough to understand the important parts of phrases like "At 0 °C, at the limit of zero pressure, the compressibility is 5.1×10−10 Pa−1", I can understand this phrase: "The low compressibility of water means that even in the deep oceans at 4 km depth, where pressures are 40 MPa, there is only a 1.8% decrease in volume." http://en.wikipedia.org/wiki/Properties_of_water#Density_of_water_and_ice http://en.wikipedia.org/wiki/Properties_of_water#Density_of_...
- prewett 15y ago
  Why -30C? I'd be really surprised if the bottom of the ocean were much below 4C, since that's the greatest density (62.4 lbs/ft^3), see [1]. [1] http://en.wikipedia.org/wiki/Properties_of_water http://en.wikipedia.org/wiki/Properties_of_water (see sidebar)
  - jholman 15y ago
    Oh, my bad. I misrecalled a detail from the featured article, thinking it had claimed that temperatures were very very low, so I picked the lowest temperature in that sidebar as a rough approximation. Actually, TFA says "near freezing", which certainly much closer to 4C than to -30C. Silly me.
Florin_Andrei 15y ago
Ah, ok, so "high density" is a thing, it's a term with a specific meaning. I was trained as a physicist, not as an engineer, and to me "high density" means "lead". :)

by learc83 15y ago

deleted 15y ago

[deleted]

jholman 15y ago

Since I was curious about the relative densities, I looked it up and asked Google to convert to your archaic units. Water, at -30C, is around 60 lbs/ft³, so indeed the foam is denser. I was _going_ to claim that water is denser still, way down deep in the ocean. But I thought I'd check it out first, and although I'm not well-educated enough to understand the important parts of phrases like "At 0 °C, at the limit of zero pressure, the compressibility is 5.1×10−10 Pa−1", I can understand this phrase: "The low compressibility of water means that even in the deep oceans at 4 km depth, where pressures are 40 MPa, there is only a 1.8% decrease in volume." http://en.wikipedia.org/wiki/Properties_of_water#Density_of_water_and_ice http://en.wikipedia.org/wiki/Properties_of_water#Density_of_...

prewett 15y ago
Why -30C? I'd be really surprised if the bottom of the ocean were much below 4C, since that's the greatest density (62.4 lbs/ft^3), see [1]. [1] http://en.wikipedia.org/wiki/Properties_of_water http://en.wikipedia.org/wiki/Properties_of_water (see sidebar)
- jholman 15y ago
  Oh, my bad. I misrecalled a detail from the featured article, thinking it had claimed that temperatures were very very low, so I picked the lowest temperature in that sidebar as a rough approximation. Actually, TFA says "near freezing", which certainly much closer to 4C than to -30C. Silly me.

Florin_Andrei 15y ago

Ah, ok, so "high density" is a thing, it's a term with a specific meaning. I was trained as a physicist, not as an engineer, and to me "high density" means "lead". :)