4 ms·

> Chemist here. We use centrifuging to separate components of a suspension by weight. Pitch is a suspension. The last bit is puzzling: Are all suspensions flu

> Chemist here. We use centrifuging to separate components of a suspension by weight. Pitch is a suspension. The last bit is puzzling: Are all suspensions fluids? And all fluids are viscous (even non-newtonian)? If so, why do we need an experiment to prove that pitch --a suspension-- is a fluid and is viscous? On the point of using a centrifuge. Is there something particularly special about gravity on earth that does not affect pitch? In other words, if we exposed pitch to 0.1x, 1x, 10x, 100x and 1000x g, at what point would the fundamental characteristics of the material invalidate the experiment. Are fluids and their viscosity only defined on earth (ignoring thermal and other non-gravitational effects)? Perhaps pitch is a viscous fluid on earth but a solid on the moon, where gravity is 1/6 of ours? Is this experiment only valid at 9.8 m/s^2 then? What's the tolerance based on the substance under test?

samatman 13y ago
No, all suspensions are not fluids. Amorphous rocks, for an example, often contain microcrystals in suspension. They will not flow under any circumstances. Glass can have all sorts of powders suspended in it, and is not a fluid. Pitch can be proven to be a suspension via distillation. To prove it's a fluid, it must be observed to flow, to form a droplet, and to detach that droplet in the manner of a fluid.
- ColinWright 13y ago
  Mathematician here. Yes, this is about to be a nitpick, and I apologize in advance. However: > No, all suspensions are not fluids. I think what you mean is "No, not all suspensions are fluids." Interpreting what you said literally would imply that anything that is a suspension is definitely not a fluid. And I know one can interpret what you said according to common sense to deduce that you didn't mean that, and that since some suspensions definitely are fluids, then you must have meant that there are suspensions that are not fluids. But this is about science, and where possible, I believe we should be precise. I believe it matters.
  - blahedo 13y ago
    Linguist here.[0] Yes, this is a nitpick, but no apologies, because this is Hacker News. :) Unfortunately, languages don't always work the way that logicians would like them to do. Yes, we can read that sentence as the English-language summary of a logical formula (something like ∀x [Sx -> ¬Fx]), but English (and many other languages) treat the scope of the "not" as ambiguous. It's not a matter of "interpreting what you said literally", because there are multiple correct literal interpretations of what he said---he is not using a metaphor or anything. There are many cases where "not" can scope out to an enclosing quantifier (one of the better-known is "All that glitters is not gold", famously by Tolkien), and this is not just because all these speakers are in error. [0] Also computer scientist, but I'll wear my linguist hat for now.
    - ok_craig 13y ago
      The mathematician had a better point.
    - Zuider 13y ago
      For me, It violates the principle of least surprise to encounter a sentence like "all birds do not fly". I have to do a double take and reinterpret the sentence to realise its intended meaning.
    - andrewflnr 13y ago
      IMO, if "all these speakers" collectively make the language ambiguous, then clearly someone is in error, because unambiguity[0] is essential to the primary purpose of language: communication. This has nothing to do with whether one is a logician or mathematician. A sentence like "all X are not Y" naturally associates like "all X are (not Y)". Usually modifiers attach to the closest thing they can, as a matter of well-established convention. So if someone decides they want that to mean "not (all X are Y)" and expects me to understand it, I'm going to go ahead and say they're the one in error. Sorry, Tolkien. [0] Is that a word? Chromium spell-check doesn't like it. I have lightened up on neologisms, as long as it's clear what they mean.
      - 13y ago
samatman 13y ago
To answer your second question, there is some critical number, which we do not know empirically, after which pressure will separate pitch. We could apply some higher acceleration for a shorter time, but that acceleration would have to be highly consistent, and there is no way to shorten the experiment enough to keep that equipment from being unproductive to even contemplate. Sometimes patience really is the best answer.
- robomartin 13y ago
  OK, had a break so I looked around a little to see what I could learn [1], [2], [3] and [4] are my launching points. So I read that asphalt is actually a colloid and that pitch is not the same as asphalt. The Wikipedia page on pitch [3] says it is a "viscoelastic polymer". So I have to ask. Can a polymer be a suspension or a colloid on its own or is pitch a polymer colloid in another "host" substance? [1] http://en.wikipedia.org/wiki/Suspension_(chemistry) http://en.wikipedia.org/wiki/Suspension_(chemistry) [2] http://en.wikipedia.org/wiki/Asphalt http://en.wikipedia.org/wiki/Asphalt [3] http://en.wikipedia.org/wiki/Pitch_(resin) http://en.wikipedia.org/wiki/Pitch_(resin) [4] http://en.wikipedia.org/wiki/Colloids http://en.wikipedia.org/wiki/Colloids
  - samatman 13y ago
    Pitch is also a colloidal suspension, or colloid. The various polymers that make it up are not of equal weight, and there are little bits of graphite in there too. The chemistry of pitch is by no means simple, destructive distillation can go in many directions.
    - robomartin 13y ago
      Learned a lot through this thread. Thanks.

samatman 13y ago

No, all suspensions are not fluids. Amorphous rocks, for an example, often contain microcrystals in suspension. They will not flow under any circumstances. Glass can have all sorts of powders suspended in it, and is not a fluid. Pitch can be proven to be a suspension via distillation. To prove it's a fluid, it must be observed to flow, to form a droplet, and to detach that droplet in the manner of a fluid.

ColinWright 13y ago
Mathematician here. Yes, this is about to be a nitpick, and I apologize in advance. However: > No, all suspensions are not fluids. I think what you mean is "No, not all suspensions are fluids." Interpreting what you said literally would imply that anything that is a suspension is definitely not a fluid. And I know one can interpret what you said according to common sense to deduce that you didn't mean that, and that since some suspensions definitely are fluids, then you must have meant that there are suspensions that are not fluids. But this is about science, and where possible, I believe we should be precise. I believe it matters.
- blahedo 13y ago
  Linguist here.[0] Yes, this is a nitpick, but no apologies, because this is Hacker News. :) Unfortunately, languages don't always work the way that logicians would like them to do. Yes, we can read that sentence as the English-language summary of a logical formula (something like ∀x [Sx -> ¬Fx]), but English (and many other languages) treat the scope of the "not" as ambiguous. It's not a matter of "interpreting what you said literally", because there are multiple correct literal interpretations of what he said---he is not using a metaphor or anything. There are many cases where "not" can scope out to an enclosing quantifier (one of the better-known is "All that glitters is not gold", famously by Tolkien), and this is not just because all these speakers are in error. [0] Also computer scientist, but I'll wear my linguist hat for now.
  - ok_craig 13y ago
    The mathematician had a better point.
  - Zuider 13y ago
    For me, It violates the principle of least surprise to encounter a sentence like "all birds do not fly". I have to do a double take and reinterpret the sentence to realise its intended meaning.
  - andrewflnr 13y ago
    IMO, if "all these speakers" collectively make the language ambiguous, then clearly someone is in error, because unambiguity[0] is essential to the primary purpose of language: communication. This has nothing to do with whether one is a logician or mathematician. A sentence like "all X are not Y" naturally associates like "all X are (not Y)". Usually modifiers attach to the closest thing they can, as a matter of well-established convention. So if someone decides they want that to mean "not (all X are Y)" and expects me to understand it, I'm going to go ahead and say they're the one in error. Sorry, Tolkien. [0] Is that a word? Chromium spell-check doesn't like it. I have lightened up on neologisms, as long as it's clear what they mean.
    - 13y ago

samatman 13y ago

To answer your second question, there is some critical number, which we do not know empirically, after which pressure will separate pitch. We could apply some higher acceleration for a shorter time, but that acceleration would have to be highly consistent, and there is no way to shorten the experiment enough to keep that equipment from being unproductive to even contemplate. Sometimes patience really is the best answer.

robomartin 13y ago
OK, had a break so I looked around a little to see what I could learn [1], [2], [3] and [4] are my launching points. So I read that asphalt is actually a colloid and that pitch is not the same as asphalt. The Wikipedia page on pitch [3] says it is a "viscoelastic polymer". So I have to ask. Can a polymer be a suspension or a colloid on its own or is pitch a polymer colloid in another "host" substance? [1] http://en.wikipedia.org/wiki/Suspension_(chemistry) http://en.wikipedia.org/wiki/Suspension_(chemistry) [2] http://en.wikipedia.org/wiki/Asphalt http://en.wikipedia.org/wiki/Asphalt [3] http://en.wikipedia.org/wiki/Pitch_(resin) http://en.wikipedia.org/wiki/Pitch_(resin) [4] http://en.wikipedia.org/wiki/Colloids http://en.wikipedia.org/wiki/Colloids
- samatman 13y ago
  Pitch is also a colloidal suspension, or colloid. The various polymers that make it up are not of equal weight, and there are little bits of graphite in there too. The chemistry of pitch is by no means simple, destructive distillation can go in many directions.
  - robomartin 13y ago
    Learned a lot through this thread. Thanks.