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If you apply the same force as you would to a cup handle it order to pick up the cup, to a single atom of the surface of the cup, couldn't that remove the atom?

by drdeca 11y ago

If you apply the same force as you would to a cup handle it order to pick up the cup, to a single atom of the surface of the cup, couldn't that remove the atom? "Can be removed using a specific level of force" is then not sufficient for determining whether a collection of particles form an object. Perhaps if one instead uses some amount of force applied on the collection of particles which depends on the mass of the collection? That seems like it could be tricky, because I don't think I would generally consider fluids to be objects (in the sense we are speaking of), but I would not be too surprised if some fluid could be removed from a glass with a given level of force depending on the mass of a portion of the liquid, applied evenly over the portion, while keeping the portion of the liquid contiguous. Which would seem to indicate that and portion of the liquid is an object. However, maybe that is actually a solution, by adding the additional restriction that no part of an object is an object? (In a particular sense of object). Or alternatively, the intersection of any two objects is empty? So, the section of the liquid is not an object, because a smaller part would then also be an object, and therefore, the individual molecules would be the objects. That seems plausible to me...

pdonis 11y ago
> If you apply the same force as you would to a cup handle it order to pick up the cup, to a single atom of the surface of the cup, couldn't that remove the atom? No, because the forces holding the atoms of the cup together are much stronger than the forces holding the cup to the floor. That's the underlying physical reason why it makes sense to consider the cup as an "object".
- jacobolus 11y ago
  More to the point, if someone decides to reject that the chair is an object, that’s entirely fine, it’s just a semantic dispute, not a dispute about the underlying reality. The individual atoms (or really, electrons and quarks) which make up the chair and the floor and the air around it don’t behave differently based on what object boundaries some person attaches in their mind. Some of the atoms which the human considers to be “part of” the chair get left behind on the floor, while the bottoms of the chair legs pick some atoms up from the floor. Water molecules are constantly being traded between the chair surface and the air. And so on. The object boundary is in some sense arbitrary and porous. The way we define it is based on our own practical use and experience, and the aggregated/emergent properties which are relevant to us, since we don’t have the means to simultaneously apprehend every individual particle in our surroundings.
  - orasis 11y ago
    "The object boundary is in some sense arbitrary and porous." Yes. All objects are mind created, so indeed their boundaries are arbitrary.
- drdeca 11y ago
  Really? Not just per mass? Huh. I am somewhat surprised. Hmm, but one can scratch a cup fairly easily, can one not? (depending on the type of cup). This is removing some part of the cup. Hmm, I guess that still might take more force than picking it up? But what if one has like, a really big thing of uh, I want to say talc but I don't know how much of that one could hold up without part of it breaking off... uh, google tells me gypsum can be scratched with a fingernail, and when I try to look up its tensile strength (which I assume would be the relative measure when considering hanging a thing of it from one end of it), I get the answer of between 1 and 2 MPa at ambient temperature. Also it says gypsum board, which I assume is just a board made of gypsum? Also, I am assuming that expressing the tensile strength in MPa is force per cross section. No other interpretation comes to my mind, but I could be interpreting this number wrong. I'll call the tensile strength P. I find for the density of gypsum 803 kg/m^3 . Then, for a block of gypsum hanging from the top end, with cross section area A, with g=9.8 m/s^2 , the longest height h it could be before breaking would be found by : hAdensityg=AP hdensityg=P h=P/(densityg) h=2 MPa / ((803 kg/m^3)(9.8 m/s^2)) h=2 MPa / (8039.8 N/m^3) h=2 MPa / 8039.8 Pa/m) h=254.1 meters. So, if one had a column of gypsum 254.1 meters tall, and picked an atom at the top of it to pull up with force more than that of the whole weight of the pillar, certainly the whole pillar would not rise into the air, because its weight would be too much for the tensile strength. So, certainly it would break somewhere. If I was standing next to it near the top of it, I could scratch it with my fingernail, and so remove a part of it. But if it had much cross sectional area, the force I would need to do this would certainly be less than the force I would need to lift it. If the cross sectional area was one square meter, its weight, and so the force needed to hold it up, would be 2 million newtons (wolfram alpha tells me this is about 1/6 of the thrust of a space shuttle rocket booster at liftoff). So, I would be able to remove a small part of it, but would be clearly unable to lift it. If the force that would be needed to lift it were all applied to some atom at the top of it, it would remove some smaller part of it. I expect if enough force to lift it were to be applied to a single atom at the top, that, while it perhaps would not remove only a single atom, the part which it would remove would be quite small (perhaps only a few molecules?). Yet it certainly seems like this would be termed an object. (I guess if it was that thin it would fall over, but it can easily be imagined to be much wider, which I think would allow it to sit on the ground properly.) So then, it seems like the force needed to pull it apart is significantly less than the force needed to hold it up, yet it still seems to be an object.
kleer001 11y ago
I think by "force" I'm imagining a physics type theoretical uniform force with god-like imaginary hands as opposed to a engineering type force in real life with hands and levers.

pdonis 11y ago
> Really? Not just per mass? Yes. Think of it this way: if the force you used to pick up the cup could remove atoms from the cup, then you wouldn't be able to pick it up; when you tried, you would just come away with some atoms, instead of the whole cup. > if one had a column of gypsum 254.1 meters tall, and picked an atom at the top of it to pull up with force more than that of the whole weight of the pillar, certainly the whole pillar would not rise into the air, because its weight would be too much for the tensile strength Yes. With typical materials that cups are made of, you could probably make the column somewhat taller; but in any case, 254.1 meters is way larger than a cup, and weighs a lot more, which is why you don't have trouble picking up a cup, even though you would if you had a tall enough column of the same material. > Yet it certainly seems like this would be termed an object. If you choose to, sure. The term "object" is not given by physical law; it's a human convention. Obviously there are going to be edge cases where the term's application becomes somewhat strained.
- drdeca 11y ago
  But I can't apply force to individual atoms of the cup. I can only apply force on a large number of the atoms of the cup at once. So, it seems to be that even if, were I to apply the entire force to a single atom of the cup, the atom would be removed, that would not impact my ability to pick up a cup, because I cannot apply the entire force to a single atom of the cup, instead, each atom of the cup which I apply force to has a much smaller force that I put on it. ___ What I am talking about is if I were to apply the total force I apply on the cup to a single atom of the cup. If I took a thin thread strong enough to support the weight of the cup, and threaded it through the handle of the cup, I would be applying the same total force to the cup, and I would be applying it to a much smaller number of atoms, but I think the number of atoms the force would be applied across would still be very large. Perhaps a needle would be a better example (it would be hard to balance, but that is only a practical matter) But then it seems to me that if I were to apply the force needed to lift the cup, on an area the same as that at the end of a needle, it seems quite likely that the needle would scratch the cup (and, in doing so, displace some of the atoms of the cup). Therefore, it seems that the amount of force needed to remove an atom from a cup, may be less than that needed to lift the cup (at least for relatively heavy, and not all too hard, cups). And, as far as a radius of an atom is a meaningful concept (which is, mostly, I think), it seems the radius is generally at most around 260 pm, so, a square bound around it (which should be in a sense an overestimate) should have an area of .2704 square nanometers. When I look up the surface area of a needle, I find that its about 12.6 mm^2 (on the lower end of the estimates). So then, the head of a pin would then be around the surface area of 4*10^13 atoms, and then, because of the space between the atoms in the cup which I might have neglected to consider, maybe drop off a few orders of magnitude (lets say, 4 orders of magnitude. I think that seems safe.) So then, if you took all the force that is being applied to the cup by the needle, and instead applied it to a single atom, the amount of pressure being applied somewhere on the cup would then be around 10^9 times as much. Generally I don't think it seems all that hard to scratch a cup with a needle, but perhaps applying force to a single atom would not be as effective as applying half the force each to two atoms, at removing them from the cup. So, another few orders of magnitude at most I'd guess. So then, scratching the cup with a needle is not all that much harder than lifting it, If the total force from the pin when scratching the cup were all on a single atom, the pressure would probably be at least 10^9 as much (to the degree that pressure makes sense in this context) removing a single atom probably does not require 10^3 times the force to remove due to the fact that the other atoms nearby do not have a similar force applied to them, I don't think (? but maybe it does?). So, with the pressure from putting the force on a single atom instead of using a pin being 10^9 times more, I think then the force on that single atom would be 10^9 times more than the average force on a given atom when it is spread over the pinhead surface, and because I think it probably doesn't need 10^3 times as much more force to remove an atom when the surrounding atoms are not experiencing similar forces, or, at least doesn't need 10^9 times as much, I think the force used to scratch a cup with a needle, if applied to a single atom on the surface of the cup, would probably remove that atom from the cup. And because the force needed to scratch the cup does not seem much more than that needed to lift a heavy cup, I think using the force that would be needed to life a heavy cup, would, if applied to a single atom on the surface of the cup, be enough to remove the atom from the cup. _________________ I think a more relevant measure for whether something is an object might be whether it takes more than a given amount of pressure to remove parts of it, instead of taking a given amount of force. (or force per mass, or force per mol. . But it seems like pressure might work well?) __________________ uh, I've been assuming that you are, like me, just trying to reason this out, as opposed to actually, unlike me, really knowing the physics behind how materials stay together. If that is not the case, oops, I have made an error. _________________ regarding "object" being a human convention: Sure, but seeing as the gypsum pillar seems to be something that people would classify as an object, it seems like it would make sense to revise whatever definition we choose for "object" to include such a pillar. Although, when I think about it more, maybe such a pillar might be best not considered an object, so much as something that, each of a certain type of parts of it would be an object if the rest of it were not there? I guess it is useful to be able to talk about whether something is an object even in microgravity, so I guess maybe it makes sense to choose some amount of pressure\whatever needed to pull something apart, rather than whether it can be picked up without falling apart. hmmm... ok I'm thinking pressure might not be quite right either? I'm kind of confused because http://sites.bio.indiana.edu/~hangarterlab/courses/b373/lecturenotes/water/waterintro.html http://sites.bio.indiana.edu/~hangarterlab/courses/b373/lect... seems to say that water has a higher tensile strength than gypsum, which doesn't seem to make sense to me. I'm guessing maybe that is only in a particular situation? hmm...
  - pdonis 11y ago
    > I can't apply force to individual atoms of the cup. I can only apply force on a large number of the atoms of the cup at once. But that number is still much smaller than the total number of atoms in the cup. So you're depending on a relatively small number of atoms to transmit the force you exert to a much larger number of atoms. > If I took a thin thread strong enough to support the weight of the cup, and threaded it through the handle of the cup, I would be applying the same total force to the cup, and I would be applying it to a much smaller number of atoms, but I think the number of atoms the force would be applied across would still be very large. You're right. The number of atoms would still be way too large to introduce any issues with removing atoms from the cup instead of lifting the cup, at least for any material that's reasonably solid. (If you want to test that statement, try lifting an ordinary cup with a very thin thread. You might break a styrofoam or paper cup, but you won't break a ceramic coffee mug.) To really apply a force to a single atom, you would have to use special equipment (which I'm not even sure exists at our current level of technology). If you could, in fact, apply the same force you apply to lift the cup to a single atom, it might indeed be sufficient to remove that single atom from the cup (I haven't looked up specific numbers) instead of lifting the entire cup. (In fact, it might depend on what the cup was made of: a styrofoam cup would certainly lose an atom, even a ceramic cup might, but a cup made of diamond or carbon nanotubes might not. Material strengths vary over many orders of magnitude.) > removing a single atom probably does not require 10^3 times the force to remove due to the fact that the other atoms nearby do not have a similar force applied to them, I don't think (? but maybe it does?) As I just noted, material strengths (which are a measure of the forces between atoms) vary over many orders of magnitude. Certainly more than 3; possibly as many as 9. So, as I said above, it might well depend on the material. > I've been assuming that you are, like me, just trying to reason this out, as opposed to actually, unlike me, really knowing the physics behind how materials stay together. If that is not the case, oops, I have made an error. I'm basing my statements on the actual physics involved. > the gypsum pillar seems to be something that people would classify as an object, it seems like it would make sense to revise whatever definition we choose for "object" to include such a pillar. That's up to whoever is using the term. Different people use the term "object" for different purposes. In any case, this is really a question about language, not physics. > seems to say that water has a higher tensile strength than gypsum Note that this is for a particular case, very thin columns of water in capillary tubes, where the water can actually act somewhat like a solid, at least in resisting tensile forces (i.e., being pulled apart). A liquid in bulk doesn't really have a meaningful tensile strength.

drdeca 11y ago
Thank you for your response. >If you could, in fact, apply the same force you apply to lift the cup to a single atom, it might indeed be sufficient to remove that single atom from the cup (I haven't looked up specific numbers) instead of lifting the entire cup. (In fact, it might depend on what the cup was made of: a styrofoam cup would certainly lose an atom, even a ceramic cup might, but a cup made of diamond or carbon nanotubes might not. Material strengths vary over many orders of magnitude.) I think a less careful form of this (e.g. not including stuff about different materials) was most of what I was trying to say. I thought "force required to remove a part" was insufficient, because it doesn't include anything about how the force is applied, or how small the part removed can be, etc. > Certainly more than 3; possibly as many as 9. Ok, thanks. My physical intuition doesn't tend to be all that great. Thanks for correcting me on this point. > I'm basing my statements on the actual physics involved. I am trying to do that, looking up information about different materials, but I don't have any actual experience with like, materials science or whatever (not sure what the right term is), and I suddenly was wondering if you did have experience with that, and that from that perspective I might be obviously wrong. > Different people use the term "object" for different purposes. Yeah, I didn't mean to suggest that people ought to use a single meaning for the term. I was just trying to think about what precise definition would be most(?) useful for general use, when some other one hasn't been chosen for whatever reason. So like, what somewhat precise definition fits best with the most people's intuitions/usage of the term. >Note that this is for a particular case, very thin columns of water in capillary tubes, where the water can actually act somewhat like a solid, at least in resisting tensile forces (i.e., being pulled apart). A liquid in bulk doesn't really have a meaningful tensile strength. Ok, that makes sense. (I'm a little surprised about that last part, as I was imagining like, a blob of water in microgravity (with air pressure), and pulling it apart (somehow), but I guess applying force to it would cause it to deform before splitting in two, so maybe the cross sectional area wouldn't be well defined (but isn't that kind of like other materials also? oh well.)? Or I guess the force needed could depend on the amount of water or something in a complicated way which doesn't correspond nicely with tensile strength? (I had been considering if the "tensile strength" of free floating water was really small but nonzero, then there might be some value that all "objects" have a tensile strength above, but that probably doesn't make much sense.)) Again, thank you for your response, and for correcting me on some things I was wrong about.