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**Ask a monkey a physics question thread**

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  1. #1651
    MadMojoMonkey's Avatar
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    Quote Originally Posted by BananaStand View Post
    So what you're saying is, I've made an unprecedented discovery.
    What I'm saying is, what you're saying is literally the opposite of both unprecedented and discovery.

    Your position on this has its appeal. There is a consistency to it. It also makes predictions. That's a hallmark of good science.
    ... as many have pointed out before you
    However, plenty of those predictions don't hold up to observations, e.g. the existence of dark energy (whatever it may turn out to be).
    Which has been discovered by other people, but apparently not you, yet.

    I respect that you hold out for when the data shows your assertion doesn't hold up to observations before you yield your position.
    It's silly that the data is well and truly in, and you clearly haven't internalized it, yet you persist that your assertions are still correct.

    Quote Originally Posted by BananaStand View Post
    If you don't watch your attitude, I might not mention you in my nobel prize acceptance speech.
    I find it great that you are openly skeptical of what I'm dishing out, here.
    I find it mostly amusing that you come here to tell me I'm wrong about physics.
    Admittedly, I find it mildly irritating that you put forth such brazen confidence in assertions that are demonstrably false.

    It would be hubris to assume I hold no misconceptions.
    This thread invites challengers to poke holes in what I understand and can explain (as simply and clearly as possible).
    You might be amused by my reaction when they made me chase down the rabbit hole of virtual particles. Turns out it's a lot of hand waving and talk about these things which cannot be observed by definition.

    If a virtual particle is observed, it is NOT a virtual particle, by definition.
    THIS IS NOT WHAT I SIGNED UP FOR!!!
  2. #1652
    How the fuck does ice evaporate?
  3. #1653
    OngBonga's Avatar
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    It doesn't. It either melts, or sublimates.
    Quote Originally Posted by wufwugy View Post
    ongies gonna ong
  4. #1654
    Quote Originally Posted by OngBonga View Post
    It doesn't. It either melts, or sublimates.
    And how exactly does that happen inside a freezer?

    I pour water into ice cube trays. I put ice cube trays into freezer. Water turns to ice.

    If you don't use that ice, pretty soon it just disappears.

    Whuzzupwitdat
  5. #1655
    OngBonga's Avatar
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    I have no fucking idea, it shouldn't melt or sublimate in a freezer.

    Sublimate is just the proper word for evaporate when something turns straight from solid to vapour. It happens with dry ice... carbon dioxide in solid form sublimates into a gas without being a liquid. But we're talking about water here, not CO2. Ice doesn't sublimate, not in normal conditions at least.

    So why the fuck is your ice disappearing? Is it next to a fan that blows out cold air? That might strip the ice into powder over time. Otherwise, I'm out of ideas.
    Quote Originally Posted by wufwugy View Post
    ongies gonna ong
  6. #1656
    OngBonga's Avatar
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    Aha, it seems that the process that is causing your ice to disappear is indeed sublimation. How surprising.

    You have a better freezer than I do. It doesn't happen in mine because there's a shit ton of frost. Yours is likely an anti-frost freezer which warms the frost on a coil, causing it to melt and drip into a pan. This means the air in the freezer is dry as fuck, ie very close to zero humidity, so the top layer of ice molecules exposed to the air can sublimate. In my freezer, every time I open the door, I add mosit air to it, which means conditions are not ideal for sublimation. The air isn't dry.
    Quote Originally Posted by wufwugy View Post
    ongies gonna ong
  7. #1657
    So ice becomes not-ice despite constant freezing conditions?

    Maybe this is why glaciers are melting. Maybe global warming has nothing to do with it.
  8. #1658
    MadMojoMonkey's Avatar
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    Ong is correct, here.



    GG

    @bananananana: Did he answer your question?
  9. #1659
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    Quote Originally Posted by BananaStand View Post
    So ice becomes not-ice despite constant freezing conditions?

    Maybe this is why glaciers are melting. Maybe global warming has nothing to do with it.
    Posit: This sublimation is a factor
    Posit: which hasn't changed in millenia (on a short estimate).

    Hypothesis: Whatever changes we are currently observing are not likely due to the stimulus which is not and has not been changing.
  10. #1660
    Quote Originally Posted by MadMojoMonkey View Post
    @bananananana: Did he answer your question?
    If I say 'yes' then you'll probably be disappointed. I can tell there is a detailed scientific explanation inside you that is just aching to burst out.
  11. #1661
    MadMojoMonkey's Avatar
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    Nah... it's high school chemistry that I'd rather avoid, honestly.
  12. #1662
    Quote Originally Posted by MadMojoMonkey View Post
    Nah... it's high school chemistry magic that I'd rather avoid dont understand, honestly.
    Fixed your post
  13. #1663
    OngBonga's Avatar
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    Quote Originally Posted by BananaStand View Post
    So ice becomes not-ice despite constant freezing conditions?
    Yep, just like water becomes vapour despite the not-boiling conditions.
    Quote Originally Posted by wufwugy View Post
    ongies gonna ong
  14. #1664
    If your'e going to reduce molecular density, don't you need to introduce some kind of energy into the equation?

    how is the lack of humidity doing that?
  15. #1665
    MadMojoMonkey's Avatar
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    Quote Originally Posted by BananaStand View Post
    If your'e going to reduce molecular density, don't you need to introduce some kind of energy into the equation?

    how is the lack of humidity doing that?
    Thermal energy is averaged out to a single temperature, but that average represents the middle of a bell curve of energies.

    The tails of the curve are occupied energy / temperature states. I.e. there are some "hot" and some "cold" regions interspersed throughout the microscopic scales of anything which is considered in thermodynamic equilibrium. (Note that by "hot" and "cold" I mean relative to the mean temp)

    The occasional "really hot" particle interacts with one molecule of ice, sublimating it. Now, that humidity is not left in the air, but condensed out, leaving dry air. If the air isn't dry enough, the sublimated water will condense back out like dew, leading to frost, as ong described.

    The low humidity doesn't really help the situation so much as it reduces an inhibiting factor. Air can only hold so much water suspended in it.
    Google relative humidity and dew point for more info.
  16. #1666
    OngBonga's Avatar
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    Introduce energy? There is already a shit ton of energy in the freezer. It's a couple of hundred degrees Kelvin in there. When a molecule of ice sublimates, then it takes heat from the air... the air cools down a fraction.

    Humidity plays a role because once the air is saturated, no more evaporation can take place. I assumed evaporation was zero, and therefore humidity is also zero, in a freezer. Seems like I'm wrong.

    So long as relative humidity is lower than 100%, then evaporation can take place. How much depends on temperature, pressure and relative humidity. My freezer's RH will be 100%, because there is no process which is removing the moisture from the air which I add when I open the door. At 100% RH, no evaporation takes place. Your freezer will have a lower RH, fuck knows how much lower but it's under 100%. Thus, evaporation, and indeed sublimation, can take place, because RH is <100%, and there is energy in the air. The molecules of vapour will eventually come into contact with the coil, and be removed from the system, thus reducing RH and allowing further sublimation.

    If ice loss is a problem, you could simply seal them in something air tight. Problem solved.
    Quote Originally Posted by wufwugy View Post
    ongies gonna ong
  17. #1667
    Quote Originally Posted by MadMojoMonkey View Post
    The occasional "really hot" particle interacts with one molecule of ice, sublimating it.
    Huh? How do you sublimate a single molecule? Isn't the state of matter (solid/liquid/gas) related to the configuration of many molecules? In other words, can you say that a single molecule is liquid, gas, or solid? And if so, wouldn't it always be solid?

    Now, that humidity is not left in the air, but condensed out, leaving dry air.
    Out where? I don't have any kind of fancy frost control gadgets on my freezer like Ong suggested.

    If the air isn't dry enough, the sublimated water will condense back out like dew, leading to frost, as ong described.
    Right, but why does it move first? In other words, why doesn't the sublimated particle re-condense immediately back onto the ice cube from whence it came?
  18. #1668
    Quote Originally Posted by OngBonga View Post
    If ice loss is a problem, you could simply seal them in something air tight. Problem solved.
    Crawl into your freezer and shut the door. Let me know if it's air-tight
  19. #1669
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    Quote Originally Posted by BananaStand View Post
    Crawl into your freezer and shut the door. Let me know if it's air-tight
    Things go over your head easily, don't they?

    Yes a freezer is air tight. However, the air inside the freezer is coming into contact with a heated coil. You need to isolate the ice cubes from air that is coming into contact with this coil.
    Quote Originally Posted by wufwugy View Post
    ongies gonna ong
  20. #1670
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    Quote Originally Posted by BananaStand View Post
    Huh? How do you sublimate a single molecule?
    How else could it possibly occur? All chemical processes happen on the molecular / atomic level.

    Quote Originally Posted by BananaStand View Post
    Isn't the state of matter (solid/liquid/gas) related to the configuration of many molecules?
    Yes and no. Each particle is in its state based on its "neighbor interactions." Specifically for water, if its movement is basically defined by hydrogen bonds, then it's an ice molecule. If it is frequently interacting with neighboring molecules, but not via stable hydrogen bonds (its specific neighbors are constantly changing), then it's liquid water. If its movement is largely unrestrained, aside from occasional (actually, well defined, here, despite the sound) interactions, then it is water vapor or steam.

    Under certain conditions (not in a typical household freezer), the phases of matter can vary via a smooth transition, and not a sharp boundary.

    Quote Originally Posted by BananaStand View Post
    In other words, can you say that a single molecule is liquid, gas, or solid? And if so, wouldn't it always be solid?
    No, there are tons of outlier cases, but for water near STP, this is well-defined for each particle, as I briefly stated above.

    Quote Originally Posted by BananaStand View Post
    Out where? I don't have any kind of fancy frost control gadgets on my freezer like Ong suggested.
    You almost definitely have a frost free freezer. They haven't made the other kind in decades, AFAIK.
    ...
    BUT
    ...
    IDK what you've got.

    You either have a freezer whose walls gather a couple of inches per year of frost, or you have a frost-free freezer.
    Have you seen / do you recall those old freezers that would slowly crust over inside until they were a solid block of frost?


    Quote Originally Posted by BananaStand View Post
    Right, but why does it move first? In other words, why doesn't the sublimated particle re-condense immediately back onto the ice cube from whence it came?
    The air in the freezer is ~200 K and zipping about real fast like. Interactions are rare on the length scales of the particles... many hundreds or thousands of particle diameters may be covered between collisions with another particle... but they are still common in time, 'cause the particles are still moving about rapidly and there's about 1 mole of particles per liter of air, so plenty of particles in the air in the freezer to interact with.
  21. #1671
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    Quote Originally Posted by OngBonga View Post
    If ice loss is a problem, you could simply seal them in something air tight. Problem solved.
    I endorse this experiment.

    Place an ice tray in a ziplock bag or equivalent and another which is not sealed or "normal."

    Wait a while (however long you would normally notice a loss of ice).

    Compare results.

    Repeat for fun and excitement!
  22. #1672
    If good science is repeating experiments and getting the same result you both expecting BS to not dismiss everything you say and assume he's right is bad science.
  23. #1673
    OngBonga's Avatar
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    Have you seen / do you recall those old freezers that would slowly crust over inside until they were a solid block of frost?
    I reckon my freezer is currently at around 25% capacity, with the other 75% being ice.
    Quote Originally Posted by wufwugy View Post
    ongies gonna ong
  24. #1674
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    Quote Originally Posted by OngBonga View Post
    I reckon my freezer is currently at around 25% capacity, with the other 75% being ice.
    At least your computer's tech level is in this millennium, I guess.

    Pro Tip: Using a chisel to clean out the frost is harder than it sounds. If you do this to your dad's deep freeze, he'll probably be real mad about it. He probably wont even notice the lack of frost in his freezer, he'll be so mad.

    Childhood memories.
  25. #1675
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    Dude you're a science guy, why the fuck doesn't little mojo do something more creative than chip away at it with a chisel?

    The least you could do is heat the chisel up with boiling water.
    Quote Originally Posted by wufwugy View Post
    ongies gonna ong
  26. #1676
    Quote Originally Posted by OngBonga View Post
    I reckon my freezer is currently at around 25% capacity, with the other 75% being ice.
    Have you ever heard of defrosting your freezer, or are you waiting till it's 100% frosted over.

    The nice side effect is that you should end up with some large blocks of ice you can use to cool your computer room. Assuming of course it isn't already full with banana plants.
  27. #1677
    Quote Originally Posted by OngBonga View Post
    Dude you're a science guy, why the fuck doesn't little mojo do something more creative than chip away at it with a chisel?

    The least you could do is heat the chisel up with boiling water.
    Depends on his age really - even a very bright five year old is pretty dumb. I recall being that age and testing the hypothesis that a razor blade was sharp by running my thumb over it. Hypothesis 1 confirmed. I immediately went from that to testing the hypothesis that a tissue could stop the bleeding. Hypothesis 2 disproven.
  28. #1678
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    Quote Originally Posted by Poopadoop View Post
    Have you ever heard of defrosting your freezer, or are you waiting till it's 100% frosted over.

    The nice side effect is that you should end up with some large blocks of ice you can use to cool your computer room. Assuming of course it isn't already full with banana plants.
    Obviously you haven't heard of defrosting, considering you're assuming there will be ice left afterwards. I'm not gonna do a mojo and get the hammer and chisel out.

    I intend to do this very soon, ie when the remaining food in there is eaten. The plan is to leave it outside and open on a hot day. The ice doesn't stand a fucking chance.
    Quote Originally Posted by wufwugy View Post
    ongies gonna ong
  29. #1679
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    Quote Originally Posted by OngBonga View Post
    Dude you're a science guy, why the fuck doesn't little mojo do something more creative than chip away at it with a chisel?
    Big Mojo claims buoys his ego by pretending he's smart 'cause he's done so many dumb things and knows not to do them now.

    Quote Originally Posted by OngBonga View Post
    The least you could do is heat the chisel up with boiling water.
    ... and then unplug the freezer and leave the hot chisel inside?

    'Cause the walls just aren't build to sustain those impacts. I never hit the wall directly, but it was cracked is several places, nonetheless.

    ***
    Since you actually have an old frosty:
    Was my estimate for frost creep about right? Is it thickening at a rate of ~2 - 3 inches per year?
  30. #1680
    Quote Originally Posted by OngBonga View Post
    Obviously you haven't heard of defrosting.
    Obviously you haven't tried defrosting a freezer with large amounts of frost. What happens is the ice on the walls melts fastest cause it's metal and big chunks slide off.

    Try it, you'll like it.
  31. #1681
    Which is warmer? The ground, or the air two feet above the ground?
  32. #1682
    OngBonga's Avatar
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    Quote Originally Posted by mojo
    Was my estimate for frost creep about right? Is it thickening at a rate of ~2 - 3 inches per year?
    I share a house with a friend, and I've only lived here 6 months. It's a great deal more than 2-3 inches in that time alone. I'm pretty sure it's fucked.

    It does freeze things though, so it'll do.

    Quote Originally Posted by poop
    Obviously you haven't tried defrosting a freezer with large amounts of frost. What happens is the ice on the walls melts fastest cause it's metal and big chunks slide off.
    Obviously you have no idea how I like to go about tasks.

    Put freezer outside on hot day where it can drain. Go back inside. Put kettle on. Make tea. Roll spliff. Talk shit on internet. Perhaps play a game of chess. Maybe even go outside and sit in the garden for a bit. After all that hard work, finally go back to freezer and laugh at the feebleness of ice.
    Quote Originally Posted by wufwugy View Post
    ongies gonna ong
  33. #1683
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    Quote Originally Posted by BananaStand View Post
    Which is warmer? The ground, or the air two feet above the ground?
    I'm gonna go out on a limb and say... it depends.
    Quote Originally Posted by wufwugy View Post
    ongies gonna ong
  34. #1684
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    In case that's too cryptic, I'll elaborate...

    It depends on the temperature of the air and the ground.

    In case it seems like I'm being a sarcastic cunt, I'll simply say that I think that in some cases, the ground is warmer, and in other cases, the air is warmer.

    Tundra in winter and tundra in summer probably provides an example where the same ground can fluctuate between colder and warmer than the air above it.
    Quote Originally Posted by wufwugy View Post
    ongies gonna ong
  35. #1685
    Quote Originally Posted by OngBonga View Post
    I'm gonna go out on a limb and say... it depends.
    On what?

    The National Forest here has been invaded by insidious corporate interests disguised as environmental activists. And they have a stranglehold monopoly on all of the prime campsites in the region. They are also notoriously crowded and loud.

    Since the land is public, you can camp anywhere you want. There are some rules. You need to be 200 feet from a trail, 200 feet from rivers, lakes, or ponds. YOu have to be 1/4 mile from any road. And you have to be 1/4 mile from any of the established "corporate" campsites. That leaves a few hundred thousand acres where you can do whatever the fuck you want.

    Except, almost all of that is on a steep slope, densely wooded, or really far from a usable water source. It's possible, but not exactly easy to find a suitably flat spot to put a tent.

    The solution, hammocks.

    I've got this, and I'm fucking dying to try it out.
    https://www.rei.com/product/882625/e...lenest-hammock

    I can't carry this setup and a tent, so I have to pick one. I'm anxious to try the hammock, but I also don't want to be stuck freezing my ass off all night while I'm 10 miles into the wilderness.

    Temps are looking to be in the low 40's overnight and some rain showers are likely.

    Assuming that I'm using the same insulating pad, and sleeping bag with either setup, would I be warmer in a tent, or in the hammock
  36. #1686
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    Quote Originally Posted by BananaStand View Post
    I've got this, and I'm fucking dying to try it out.
    https://www.rei.com/product/882625/e...lenest-hammock

    I can't carry this setup and a tent, so I have to pick one. I'm anxious to try the hammock, but I also don't want to be stuck freezing my ass off all night while I'm 10 miles into the wilderness.

    Temps are looking to be in the low 40's overnight and some rain showers are likely.

    Assuming that I'm using the same insulating pad, and sleeping bag with either setup, would I be warmer in a tent, or in the hammock
    First of all, I envy people that can use a hammock and not have crippling back pain within an hour. It looks relaxing and practical.

    As someone who spent many years in Boy Scouts, The right sleeping bag will make all the difference in all but arctic conditions.
    Have 2 - 3 sleeping bags for hot, nice, and cold camping. Hot doesn't really need a bag, IMO, but some still use one.

    ***
    The best insulation is tiny pockets of trapped air swiss-cheesed throughout a material with low thermal conductivity... like foam pads.
    Having that insulating pad you mention under you will make a big difference, as you probably know.

    Since that's the same in both cases, the actual difference is what's under the pad.
    In the hammock, it's unrestrained air... in a tent, it's the ground. The ground has much lower thermal conductivity than the open air.
    The ground should be a bit warmer.
  37. #1687
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    On what?
    Local conditions, I would have thought. Like, season, weather, ground type, indoors or outdoors.

    That hammock looks cool. I want one.

    I reckon it will be warmer than a tent in wet conditions. Not much, but a little. It's not that the air is warmer than the ground (though it might be), it more that gas is much less dense than solid. Water at 5 degrees feels much colder than air at 5 degrees, that's because you're losing more heat thanks to your skin being in contact with a much higher concentration of colder matter. It'll be the same logic behind air and ground. The more air you're surrounded by, the less heat loss there will be.

    Also, the fact water can drain off quickly, rather than collecting in pools, will help matters.
    Quote Originally Posted by wufwugy View Post
    ongies gonna ong
  38. #1688
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    Quote Originally Posted by mojo
    In the hammock, it's unrestrained air... in a tent, it's the ground. The ground has much lower thermal conductivity than the open air.
    The ground should be a bit warmer.
    Well this contradicts what I just said, so assume I'm talking bollocks and listen to the science guy.
    Quote Originally Posted by wufwugy View Post
    ongies gonna ong
  39. #1689
    Quote Originally Posted by MadMojoMonkey View Post
    First of all, I envy people that can use a hammock and not have crippling back pain within an hour. It looks relaxing and practical.
    I used to think the same thing. Every person I've ever known who has had a hammock in their backyard admits to regretting the purchase. Either it's uncomfortable, unstable, or both. This has a lot to do with the design of the hammock. Generally those rope-net setups with crossbars on either end are just terrible for human ergonomics.

    However, based on the superficial research I've done this far, it seems that hammock technology has come a long way in just the last 8 to 10 years. These gathered-end parachute hammocks are shaped just right so that if you tilt your body so that your spine is slightly diagonal in relation to the hammock center, then you can actually lay perfectly flat.

    I actually took a long, heavy nap in this thing over the weekend and was exceedingly comfortable sleeping on both my side, and my back. I only got out because the sun went in, the wind picked up, and I was fucking freezing. I wasn't using an insulated pad, sleeping bag, or tarp though.
  40. #1690
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    Quote Originally Posted by OngBonga View Post
    I reckon it will be warmer than a tent in wet conditions.
    This shouldn't be an issue. If you have water touching your tent, you're probably doing it wrong.
    Note: the tent has a rain fly, which is a fly, not the tent. The fly should cover the top and sides of the tent, with perhaps some exposed doorway bit.

    Before you pitch the tent, picking the location is important.
    You want a subtle / gentle slope, not underneath any trees which may attract lightning or shed limbs in windy conditions.

    First, clear the tent area of any pebbles sticks, etc.
    Next, you want to lay down a waterproof tarp. Fold any overlapping bits of tarp, which are wider than the tent base, to fit. You don't want the tarp outside the tent base, but as close to the edge as is reasonable.
    Lay the unrolled tent on the tarp, with the door on the downhill edge. Fix / refold tarp if necessary, and stake the tent.
    Next, you want to take a stick or the claw end of a hammer, etc. and dig a 1/4" to 1/2" deep channel in the dirt around the back and down the sides of your tarp. It doesn't need to be wide, just a line in the dirt that will redirect any rivulets around your tent. It's primarily meant to redirect rivulets which fall off the tent's fly, so it needs to be beneath that overhang. This is not a time consuming project, just drag the tool around and visually verify that your channel isn't bad. Quick and easy. Don't over-think it. You should be able to shuffle your feet over the channel to quickly remove it when you break camp. (LEAVE NO EVIDENCE!!!)

    Finish pitching the tent.
  41. #1691
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    Quote Originally Posted by OngBonga View Post
    That hammock looks cool.
    I was expecting one of these (or something similar).


    Quote Originally Posted by OngBonga View Post
    I want one.
    Single-person hammock tent is equivalent in price range to single-person tent.
  42. #1692
    Holy shit dude. The "Leave No Trace" crowd would murder you if they saw your campsite

    I'm pretty sure that a claw hammer appears nowhere in their guidelines
  43. #1693
    Quote Originally Posted by MadMojoMonkey View Post
    I was expecting one of these (or something similar).
    Those things are crazy expensive, and I'm not really seeing the benefits.

    Compared tents or hammocks, those suspended tents seem like they're the worst of both worlds
  44. #1694
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    Quote Originally Posted by BananaStand View Post
    Holy shit dude. The "Leave No Trace" crowd would murder you if they saw your campsite
    Dude.

    Quote Originally Posted by MadMojoMonkey View Post
    Next, you want to take a stick or the claw end of a hammer, etc. and dig a 1/4" to 1/2" deep channel in the dirt around the back and down the sides of your tarp. [...] You should be able to shuffle your feet over the channel to quickly remove it when you break camp. (LEAVE NO EVIDENCE!!!)
    Quote Originally Posted by BananaStand View Post
    I'm pretty sure that a claw hammer appears nowhere in their guidelines
    I only suggested a claw hammer, because the prior instruction was to drive tent stakes, and a claw hammer is a common tool for that task.

    Whatever the implement, it's a thin, shallow trench. If you're hacking away with the hammer, you're doing it wrong.
    Just quickly drag the corner of the claw end along the dirt.
  45. #1695
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    Quote Originally Posted by BananaStand View Post
    Those things are crazy expensive, and I'm not really seeing the benefits.

    Compared tents or hammocks, those suspended tents seem like they're the worst of both worlds
    I've never used one. I think they look pretty fun... but I say the same about regular hammocks, so...
  46. #1696
    I'm not gonna pretend like I'm some kind of super educated or experienced backpacker. But I know a thing or two about a thing or two.

    So let me tell you a thing or two about these things.

    Quote Originally Posted by MadMojoMonkey View Post
    Dude.
    Dude. I'm not exaggerating. They would straight up murder your ass. The LNT people are pretty obsessive. They even try to tell people what colors are ok to wear and what aren't. Cliff Notes: They're not thrilled about orange. On the other hand, for us sensible people, orange is a great color to wear if one of your goals is to not get accidentally shot. Tradeoff: It's a terrible color to wear if someone is trying to shoot you on purpose.

    Anyway, my point is, you don't want to be killed by the organization that specializes in covering tracks. Your body will never be found.

    I only suggested a claw hammer, because the prior instruction was to drive tent stakes, and a claw hammer is a common tool for that task.
    False. If you're backcountry camping, it's highly unlikely you would carry a hammer. The weight-to-utility ratio is extra fucking bad. If you're frontcountry camping, then you're almost always at an established campsite. And if you're in an established campsite where you're legitimately concerned about water running into your tent, you should go to the manager and ask for your money back.

    Whatever the implement, it's a thin, shallow trench. If you're hacking away with the hammer, you're doing it wrong.
    Just quickly drag the corner of the claw end along the dirt.
    I'm not sure what you learned in boyscouts, but this definitely definitely definitely is a kick in the nuts to the principles of "leave no trace". The LNT organization would tell you that good campsites are found, not made.

    On the other hand, I think the LNT organization is fucking psycho, and have flouted many of their rules in the past myself. Who the fuck wastes time digging a hole before taking a dump in a forest?

    Quote Originally Posted by MadMojoMonkey View Post
    I've never used one. I think they look pretty fun... but I say the same about regular hammocks, so...
    I've never used one either, but just from what I know about tents and hammocks, I see no upside other than, they look pretty fun.

    They have advantages over regular tents in terms of your ability to find a campsite. You don't have to worry about level ground and all that. But that seems to be it as far as advantages go. Disadvantages I think are many. 1) I doubt those straps are very light 2) If you're sharing the tent with someone, there's really no way to get up to pee without disturbing the other person. 3) They're probably difficult places to change your clothes. 4) Sitting up seems iffy. 5) expensive
  47. #1697
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    Quote Originally Posted by banana
    Who the fuck wastes time digging a hole before taking a dump in a forest?
    Someone who intends to keep shitting in that same spot, I'm thinking.

    Quote Originally Posted by mojo
    Before you pitch the tent, picking the location is important.
    Yeah, usually when I go "camping" it's at a festival, and I have little choice where I set up camp. That said, I do try to avoid trees (because they become de facto toilets), and avoid the bottom of slopes (because English weather). Also, I avoid being too near toilet blocks (smelly, especially when it's hot), and main walkways because they're noisy and potentially muddy. However, even if you're well placed, you can expect a damp corner in the tent when it rains.

    Then again, I buy cheap tents to go to festivals with.

    The "leave no trace" thing is bollocks, by the way. When I go camping, I often leave scorched grass where I had a fire, and the grass under the tent will be flattened and deprived of light. I also dispose of waste food by slinging it. I'm not gonna have some jumped up little Hitler tell me to take my banana peel home. Fuck off, it's biodegradable and will decay into nutrients.
    Quote Originally Posted by wufwugy View Post
    ongies gonna ong
  48. #1698
    If I ever saw someone on a hiking trail pitch a banana peel into the woods, I would call that person a twat
  49. #1699
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    A banana peel won't last long in the woods, jeez. Some little critter will be thanking me.

    If someone called me a twat for slinging my banana peel into the woods, I'd laugh and offer them a blast on my spliff.

    This coming from a douche who doesn't bury his turds.
    Quote Originally Posted by wufwugy View Post
    ongies gonna ong
  50. #1700
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    You're not helping, ong.

    Cool it down, boys.

    This is the physics thread.
  51. #1701
    Ok - new physics question

    How come so many people suck at throwing frisbees
  52. #1702
    MadMojoMonkey's Avatar
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    IDK

    They never googled "how to throw a frisbee?"
    I found this.

    I could understand everything on that page and still not be able to throw a frisbee accurately.
  53. #1703
    LOL, I like how they explain the hammer-throw by saying "pretend you're throwing an ax"

    Like that's something people actually do.
  54. #1704
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    Yeah, I noticed that, too.

    I doubt there's a physics answer to this question. It seems more like a physiology or perhaps psychology or sociology.

    If there's a physics answer, I assume it would be unsatisfying as an answer to your question.
    E.g. some people have difficulty applying the appropriate forces and torques required to throw a frisbee so that it has a stable glide.
  55. #1705
    Getting back to the hammock thing. Suppose I used an under-quilt. It's basically a down jacket for the hammock. It wraps around the outside so that the filling doesn't get compressed, and therefore loses insulating ability.

    Would that be cumulative with a sleeping pad inside the hammock? Or would that be redundant insulation?
  56. #1706
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    Quote Originally Posted by BananaStand View Post
    Getting back to the hammock thing. Suppose I used an under-quilt. It's basically a down jacket for the hammock. It wraps around the outside so that the filling doesn't get compressed, and therefore loses insulating ability.

    Would that be cumulative with a sleeping pad inside the hammock? Or would that be redundant insulation?
    Sounds like a good solution. It would definitely be cumulative.
    So long as there is heat loss from the under-layers, additional layers will increase insulation.

    The only way it could be redundant is if the layers beneath it formed a perfect insulator.
    Perfect insulators are hard to come by.

    I guess it would be redundant if it wasn't sealed well. Like, if the breeze is getting between it and the under-layers, then its utility will dramatically diminish.
  57. #1707
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    FYI: the direction "into the page" is the imaginary portions of the complex-valued wave function. The non-spiraling cases are where the wave function exists entirely on the real line.

  58. #1708
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    So basically if you know for certain the exact location of a particle, then it could be moving at any velocity between 0 and c? Likewise, if you know the exact velocity (sorry, momentum) of a particle, then it could be anywhere in the universe?

    I have a high degree of uncertainty about this.
    Quote Originally Posted by wufwugy View Post
    ongies gonna ong
  59. #1709
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    Quote Originally Posted by OngBonga View Post
    So basically if you know for certain the exact location of a particle, then it could be moving at any velocity between 0 and c? Likewise, if you know the exact velocity (sorry, momentum) of a particle, then it could be anywhere in the universe?

    I have a high degree of uncertainty about this.
    No. In either case, your uncertainty in one of the Fourier transform pairs is 0, and 0*{anything} = 0.
    There is no way to "know for certain the exact location of a particle."
    You can know this to arbitrarily minuscule uncertainty, but not 0 uncertainty.

    The wave function goes asymptotically to 0 as it approaches +/- infinity in its space (either position space or momentum space).
    There is always a non-0 probability that the velocity, when measured, could be arbitrarily close to c in any direction.
    There is always a non-0 probability that a particle in any state could be observed in any finite volume in the universe.

    It's just that the tails of the bell-curve envelope (as illustrated in the video) are asymptotically approaching 0 with exponential decay. So the probability of observing a particle "very far" from its expected location or velocity is essentially (though not technically) 0.
    Last edited by MadMojoMonkey; 06-29-2017 at 02:24 PM.
  60. #1710
    Not physics but at what point do you need to boil all objects for them to become safe to eat assuming they are at some point safe to eat. And how do you know (generally).
  61. #1711
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    For water, it's 1 - 5 minutes, depending on your altitude, using 1 minute for sea level, and 5 minutes for ~1 mile up - say in Denver, the so-called mile-high city.

    Using this as a rule of thumb... bringing it to 100C and holding it there for a minute or so should kill any parasites or bacteria present.

    You'll know in 30 minutes to an hour if you have food poisoning.

    Actually, I just learned that most bacteria associated with food rot will not cause food poisoning. So there's that.


    I can't find any general rule of thumb for identifying if food is safe. There's such a wide variety in what people consider food.
    I found plenty of helpful sites for telling me what parts of my refrigerator are for what foods and why, though, which were fascinating. There are other sites that told me how to identify and save (if possible) common food items like fruits, veg and meats.

    Google, "how to tell if food is safe to eat"
  62. #1712
    Quote Originally Posted by MadMojoMonkey View Post
    For water, it's 1 - 5 minutes, depending on your altitude, using 1 minute for sea level, and 5 minutes for ~1 mile up - say in Denver, the so-called mile-high city.

    Using this as a rule of thumb... bringing it to 100C and holding it there for a minute or so should kill any parasites or bacteria present.

    You'll know in 30 minutes to an hour if you have food poisoning.

    Actually, I just learned that most bacteria associated with food rot will not cause food poisoning. So there's that.


    I can't find any general rule of thumb for identifying if food is safe. There's such a wide variety in what people consider food.
    I found plenty of helpful sites for telling me what parts of my refrigerator are for what foods and why, though, which were fascinating. There are other sites that told me how to identify and save (if possible) common food items like fruits, veg and meats.

    Google, "how to tell if food is safe to eat"
    The thing is I know you know better than me and will 100% google to prove me wrong. It's kind of why I ask. Basically I assume fruits are nonsense (as they are as a concept), veg lasts a week or so and meat does the same if not frozen.

    Since otherwise I've eaten a lot of broccoli, spinach. peppers, onion and green beens.
  63. #1713
    So I was clearly drunk when I posted (both of) that but basically it came down to a GMM thing where they "boil for satefy" which I think is quite an interesting question. What I was getting at with my line "Since otherwise I've eaten a lot of broccoli, spinach. peppers, onion and green beens " I don't know bar I've eaten more of those things recently than usual but it doesn't really relate to the point.

    Anyway here is my next non-physics question I expect you to google better than I do.

    Why are some animals so at home with living with humans whilst others are not? I can get why some wild animals are going to think you're a threat no matter what but when animals are brought up from birth to have humans why is this? Do they just develop a I'm going to ignore you/eat your face mechanic?
  64. #1714
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    Not sure what exactly you're asking but I think it boils down to nature vs nurture. Pretty much any animal exposed to humans from birth will be domesticated. There are pet snakes, reptiles, bears, tigers, scorpions and whatnot. At times they eat their owners, but I guess not always. The properly domesticated animals became that way over generations and generations of exposure.
    Our brains have just one scale, and we resize our experiences to fit.

    You wake me up early in the morning to tell me that I'm right? Please wait until I'm wrong.

  65. #1715
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    @CoccoBill: A tame(d) animal is not the same as a domesticated species.

    Quote Originally Posted by Savy View Post
    Why are some animals so at home with living with humans whilst others are not? I can get why some wild animals are going to think you're a threat no matter what but when animals are brought up from birth to have humans why is this? Do they just develop a I'm going to ignore you/eat your face mechanic?
    The domestication of a species happens over many generations, guided by human intervention and selective breeding.

    Different animals were "first" to be domesticated by various cultures with various indigenous fauna. Livestock could be herded and penned, but those big impaling horns are dangerous. So breed the individuals with smallest horns until there are no more horns (modern cattle). You got them in pens, but they are terrified of humans and hard to manage... except for a couple of them, which are a tad more docile. So breed the more docile ones until the herd is no longer terrified of humans... or at least isn't behaving like they are. Etc.

    Pets are in the fossil record as far back as any domesticated herd animals, if I remember my college anthropology right. Something about the oldest-known bone piles, where the bones are all from 1 species of herd animal, and were in use for generations, have humans and dog skeletons buried together near there. So it seems that some people had pet dogs in the earliest known herding communities.
  66. #1716
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    Quote Originally Posted by CoccoBill View Post
    At times they eat their owners, but I guess not always.
  67. #1717
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    Soo...these guys at the Aalto university in Finland came up with this shit. Apparently if theory holds, the universe isn't expanding. Thoughts?

    More here: https://journals.aps.org/pra/abstrac...RevA.95.063850
    Our brains have just one scale, and we resize our experiences to fit.

    You wake me up early in the morning to tell me that I'm right? Please wait until I'm wrong.

  68. #1718
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    Fine, this has noticeable effects in a crystal, but what about deep vacuum?

    "The optical force of the light pulse"
    Has what counterpart which satisfies the conservation of energy?
    I.e. it has an equal and opposite effect on what? The wavelength of the photon?
    So their argument is that photons from distant events are red-shifted not by universal expansion, but by "bleeding" energy into the intergalactic medium.
    Wouldn't this serve to heat the atoms which absorb the energy? This heat would result in blackbody emission as the atoms cool to equilibrium temperature with the microwave background, resulting in a glowing light (of lower energy photons) emitted.
    This glow is not observed, to my knowledge.

    The deep vacuum of intergalactic space is about as far from a crystal as you can get.
    The structure of a crystal is well-defined by the "neighbor interactions" of the individual atoms in the crystal.
    The interstellar (inside a galaxy, but outside a solar system) medium has approximate density of 1 atom per cubic centimeter.
    That actually seems like a lot to me, which goes to show just how many atoms per cc we are breathing on a regular basis (~2.5*10^19 molecules per cc in air, making a heap of assumptions about temperature, pressure and specific molecular composition of the air. Multiply by 2, since 99% of the air molecules are either diatomic Nitrogen or diatomic Oxygen. All told, ~5(10)^19 atoms per cc). You can see why scientists took a while to figure out that air isn't a continuum, but made of inconceivable numbers of tiny particles.

    The moral of the story is that 1 atom per cc is considered the vacuum of space, and it is characterized by the fact that atoms in the medium "rarely" interact with any other atoms. I've never heard anyone assert any correlations to crystalline behavior of a bulk solid exist in this rarefied state.

    If you divide the density of air by a billion, you get a value which is in the ballpark of the best vacuum chambers humans can produce.
    If you divide that by a billion again, you get a density ~ 50 times greater than that of the interstellar medium.
    If you divide that by 1,000 again, you get the density (approximate) of the universe as a whole. This figure (1 atoms per cubic meter) is often quoted as the density of intergalactic space (I think even by me in this thread), but that isn't where that number comes from. It's from a calculation of the total density of the universe, and not the density of the deep voids between galactic clusters. That density is therefore lower, since the density inside galaxies is higher than the universal average, then it must be lower than the average somewhere outside the galaxies.

    The intergalactic medium hasn't been directly measured, for the obvious reasons that there is no know means of sending any vessel from Earth out of this galaxy, let alone into the voids between galactic clusters.
  69. #1719
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    So their argument is that photons from distant events are red-shifted not by universal expansion, but by "bleeding" energy into the intergalactic medium.
    Can redshift not also occur as a consequence of moving out of a gravity field?
    Quote Originally Posted by wufwugy View Post
    ongies gonna ong
  70. #1720
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    Quote Originally Posted by OngBonga View Post
    Can redshift not also occur as a consequence of moving out of a gravity field?
    Yes.
    Hubble accounted for this when analyzing the spectra of distant galaxies.
    The word "distant" is poorly defined, but relevant, here. It's not that all galaxies are distant, and he's studying galaxies.

    The Hubble constant (actually Hubble was first to confirm it; it was hypothesized by Lemaitre) increases with distance. At "close" distances (lol), the local motions within a galaxy are like a mask of white noise through which it is hard to pinpoint an exact "general motion" of the galaxy. I mean... there are wide error bars on that value, because the internal motions of the galaxy are on the same order of magnitude as the recession velocity. When you look at "distant" galaxies, the local motions are about the same as the close galaxies, but their recession velocity is now much greater than their internal velocities. This allows a sharper resolution (finer error bars) on the measurement.

    The mass of the galaxy is taken into account, but with galaxies of relatively equal mass, this is a wash.
  71. #1721
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    That mostly went over my head.

    Are you saying they are certain that gravtational redshift is not the cause of the observed redshift of distant light?
    Quote Originally Posted by wufwugy View Post
    ongies gonna ong
  72. #1722
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    Quote Originally Posted by OngBonga View Post
    That mostly went over my head.
    Stuff moves around the galaxy in orbits. There is some average velocity of stuff moving in their orbits, but some of it is moving toward us, and some is moving away from us and some to the left, some to the right.

    Let's say the average speed is 100 [units].

    OK, so if I want to measure the recession velocity and the actual value I wish to measure is ~10 [units], then my result will be 10 +/- 100 [units]. That's not a very helpful result.
    However, if the actual value I wish to measure is 1,000,000 [units], then my result will be 1,000,000 +/- 100, which is a much more helpful result.

    Quote Originally Posted by OngBonga View Post
    Are you saying they are certain that gravtational redshift is not the cause of the observed redshift of distant light?
    Yes.

    These are different effects, and the universal redshift is still present after the gravitational redshift is accounted for.
  73. #1723
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    Stuff moves around the galaxy in orbits. There is some average velocity of stuff moving in their orbits, but some of it is moving toward us, and some is moving away from us and some to the left, some to the right.
    Ok I mean I get this, galaxies are basically acting like a fluid, with different densities and currents. For example, probably every river in the world will have water travelling against the flow because of eddies. The river is moving downhill at an average speed of x, but particular regions move fatser (where it's narrower) and slower (where it's wider), while a small percentage of the river is actually flowing upstream.

    Yes.

    These are different effects, and the universal redshift is still present after the gravitational redshift is accounted for.
    How are they accounting for the gravitational redshift? Wouldn't they need to know the total mass of the universe, and also the density of the centre compared to outer regions? Considering we can't be certain of its geometry, I fail to see how we can determine this with certainty.
    Quote Originally Posted by wufwugy View Post
    ongies gonna ong
  74. #1724
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    Quote Originally Posted by OngBonga View Post
    Ok I mean I get this, galaxies are basically acting like a fluid, with different densities and currents. For example, probably every river in the world will have water travelling against the flow because of eddies. The river is moving downhill at an average speed of x, but particular regions move fatser (where it's narrower) and slower (where it's wider), while a small percentage of the river is actually flowing upstream.
    Yeah.
    If you're only looking where the eddies are prevalent, it's hard to get a good measure of the overall flow.

    Quote Originally Posted by OngBonga View Post
    How are they accounting for the gravitational redshift? Wouldn't they need to know the total mass of the universe, and also the density of the centre compared to outer regions? Considering we can't be certain of its geometry, I fail to see how we can determine this with certainty.
    Hmm. Good question.

    I'm not well-versed in GR calculations, and this would be well-served by someone with a stronger background there.

    I think it's a matter of the magnitude of the gravitational potential at the source and the magnitude of the gravitational potential at the destination.

    Consider a basic conservation of energy problem, like a pendulum of mass m. It starts at rest, at some height, h2. It swings down from h2 to a new height h1, without noticeable losses to friction. We know its initial energy (mgh2) and its final energy (mgh1), so we know it's change in energy: mg(h2-h1). With a non-photon, this is usually associated with a change in speed. For a photon, this would be a change in its wavelength, i.e. a red shift or a blue shift.

    The topology in-between doesn't matter, only the end-points.
    (I think. It's GR, so maybe more convoluted that this.)
    Last edited by MadMojoMonkey; 07-07-2017 at 10:29 AM.
  75. #1725
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    I think it's a matter of the magnitude of the gravitational potential at the source and the magnitude of the gravitational potential at the destination.
    Hmm yeah ok. So do we know for certain how much dark energy or dark matter is between the start and end points? Or, at least, how much mass there is, even if we don't know what type of mass?
    Quote Originally Posted by wufwugy View Post
    ongies gonna ong

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