Difference between revisions of "Friction"

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(→‎Related: added link to yet unwritten page: * Evaluating the Friction of Rotary Joints in Molecular Machines (paper))
 
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{{Stub}}
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This page is meant to be a brief overview covering friction in …
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* gemstone based nanotech (dedicated page: [[Friction in gem-gum technology]])
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* existing nanotech (2023)
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* macrsoscale tech
  
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The essence: [[Higher throughput of smaller machinery]] is the main compensating factor <br>
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__TOC__
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and overcompensating factor for rise in friction from [[higher bearing surface area of smaller machinery]]. <br>
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Plus there are some more (over)compensating factors.
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== Qualitatively ==
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== Nanoscale friction ==
  
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'''[[Macroscale style machinery at the nanoscale]]''' has in the past received some seriously bad reputation
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== In gemstone metamaterial technology ==
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because it comes with a bunch of [[common misconceptions|mental trapdoors]] that led a a number of very smart reputational and vocal people to bad conclusions.
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One of these bad conclusions is that macroscale style machinery at the nanoscale would lead to exorbitant amounts of friction. A very wrong conclusion, as I will try to show below.
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<small>(There are other misled criticisms to the idea beside the false conclusion of exorbitant friction. For a discussion of those you may want to check out the main page about [[macroscale style machinery at the nanoscale]].)</small>
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* It is true that physics changes when the size-scale changes. But who says it changes for the worse?
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Despite [[higher bearing surface area of smaller machinery]] <br>
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* It is true that [[rising surface area|surface area grows with shrinking structure sizes]], But there are other effects that overcompensate growing surface area and these are very often overlooked.
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the [[friction in gem-gum technology]] stays manageable. <br>
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* It is true that unlike diffusion transport there is friction all the time along the whole way, but it's often overlooked that diffusion must devaluate chunks of energy at its "pit-stops" to prevent transport from running backwards and that the "change money" energy that gets left over at these "pit-stops" cannot be kept and used reused. Whereas [[machine phase systems]] allow keeping and reuse of the change.
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* It is true that there is no natural example of macro style machinery at the nanoscale (similar to the one proposed). But concluding from that that it's not possible or a worse solution is a very big fallacy. There are plenty of human invented things that exceed capabilities of nature by orders of magnitude. To give just a few examples: Bicycles, combustion engines (spaceships), copper wires (superconductors), wheels and streets, ... 
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* It is true that MEMS (microelectromechanical systems) have high friction (and very bad wear), but in case of MEMS this is due to MEMS not having atomically precise [[superlubricity|suberbublicating]] bearings but instead have a really bad signal to noise ratio in their geometry due to them being manufactured top-down.
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'''Concretely (and qualitatively) the effects that overcompensate the growing area friction increasing effect are:'''
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'''Friction not being a show-stopper is due to:''' <br>
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* rising throughput at same operating speed <br> halve size double throughput
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* (1) The throughput density of nanomachinery. – See: [[Higher throughput of smaller machinery]]
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* presence of [[superlubricity]] <br> friction proportional to speed squared
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* (2) The fact that dynamic friction of [[atomically precise slide bearing|nanoscale bearing]] drops quadratically with slowdown. – See: [[Superlubricity]]
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* minimization of travel-distance needed per chemical synthesis operation <br> dissipation falls linearly with the path travelled
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There are dissipation mechanisms that scale linear with speed but these are specific to reciprocative motions only.
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* [[Infinitesimal bearings|distribution of speed differences over multiple coplanar surfaces]] <br> speed falls linearly with number of bearing layers
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[[productivity explosion|Rising productivity with scaling down machinery]] is an especially important factor. It allows for ...
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=== (1) How nanomachineries innate high throughput density reduces friction ===
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* reducing the speed of the machinery => quadratic drop in friction power losses (due to dynamic superlubricicating friction scaling that way)
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* reducing the number of machinery => linear drop in friction power losses
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* [[Infinitesimal bearings]] can  be used to reduce friction at the intermediary scales (maybe to to extraordinary low levels)
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Minimization of travel-distance leads towards the nanofactory design and away from the molecular assembler design. <br>
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[[Higher throughput of smaller machinery]] leads to very little amount of nanomachinery needed <br>
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{{wikitodo|elaborate on that}}
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and thus to reasonably low bearing surface area within that.
  
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== Qnatitatively: Numbers ==
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=== (2) How the dynamic character of nanobearing friction can be exploited to reduce friction ===
  
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=== Highly conservative form Nanosystems ===
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Given quadratic gains in efficiency one wants to do a [[deliberate slowdown at the lower assembly levels]]
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where this type of friction is present. <br>
 +
Keeping throughput constant this means one needs to compensate for the loss of throughput with more nanomachinery. <br>
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More nanomachinery means a linear increase in losses. Quadratic gains times linear losses equals linear gains. <br>
 +
Overall linear gains in efficiency are still good and worth pursue. <br>
 +
See: [[Increasing bearing area to decrease friction]]
  
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'''Assumed:'''
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* '''Q:''' But is there enough space for accomodating more nanomachinery?
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* A [[crystolecule]] bearing with 2nm radius and 2nm length
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* '''A:''' Yes, very much so. It's "[[Higher throughput of smaller machinery]]" again.
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* Bearing stiffness k = 1000N/m
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* Bearing bumpiness [[superlubricity|incommensurability]]: R = abs(m/(m-n)) = 10
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* Bearing operating temperature: Roomtemperature 300K
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The dominant power loss contributions (Nanosystems 10.4.6.f.) give: <br>
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=== Recycle to reduce friction (not applicable to first time production) ===
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* P = 2.7*10⁻14 W / (m/s)^2 -- (for Δk{sub}a{\sub}/k{sub}a{\sub} = 0.4) or
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* P = 5.8*10⁻16 W / (m/s)^2 -- (for Δk{sub}a{\sub}/k{sub}a{\sub} = 0.003)
+
  
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So how much waste heat would one get for a reasonable desktop nanofactory?
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Also a good design averts the need to disassemble things down to nanoscopic parts if <br>
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The book Nanosystems does not even give an answer on that since energy recuperation
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only larger scale reconfigurations are needed. – See: [[Convergent assembly]] <br>
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inefficiencies in force applying mechanosynthesis and "covalent welding" block assembly likely dominate.
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This kind of aversion of frictive losses only applies to recycling though. <br>
 +
Making recycling all the more desirable end economically viable. Nice!
  
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But let's confirm that:<br>
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=== Further reading ===
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The proposed [[nanofactory]] convergent assembly system architecture (Nanosystems Table 14.1.)
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lists (as reasonable) a few times 10^17 units at the lowest [[assembly levels]].
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Nanosystems provides no info about how many bearings per unit to assume.
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But Let's assume 100 bearings per unit. This kinda seems like a reasonable
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(that is pessimistic and on the safe side) assumption. (applied [[Exploratory engineering]])
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This gives:
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* P = TODO
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* P = TODO
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Note that this is (on purpose) a rather pessimistic ("conservative") estimation.
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'''See main page: [[Friction in gem-gum technology]]''' <smalL>This contains quantitaive estimations.</small>
  
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Also the assumed 10<sup>19</sup> bearings give ''a total internal bearing sliding surface area of about: <br>
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A bit more detailed but still brief exlanations to these effects/factors <br>
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S = 200m^2''' -- Which intuitively feels like quite a lot but not overly excessive.
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can be found on the page [[How friction diminishes at the nanoscale]].
  
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== In existing nanotechnologies ==
  
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==== Side-notes regarding the Numbers given above ====
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=== Stiff ===
  
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In [[Nanosystems]] 10.4.6. some examples are calculated for 1m/s sliding speed (it gives about 80MHz for the r=2nm l=2nm bearing).  
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* Pretty much the only case where the above can already be experimentally tested (as of 2021) is in nested nanotubes and sliding graphene sheets.
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It's worth to note that a sliding speed of 1m/s is already quite fast.
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* At the microscale with [[MEMS]] there is the issue with [[stiction]]. Which may paint a misleading picture of how friction and wear scales when going down even further the sizescales.
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The actually proposed speeds are more on the order of about 1mm/s (1000 times slower).
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This makes power losses no less than one million times lower (since the two dominant drag mechanisms scales quadratically with speed).
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According to [[Nanosystems]] 10.4.6.f. the two dominating effects of for friction in [[crystolecule]] bearings (at speeds of interest ) are:
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=== Soft ===
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* band-stiffness scallering and
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* shear-reflection drag
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Other drag mechanisms (acoustic radiation, band-flutter scattering, thermoelastic damping)
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all give negligible contributions (at least for the speeds of interest).
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== Numbers from papers -- less safe (since more optimistic) ==
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It's hard to talk about friction is systems that are akin to biological cells. <br>
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It's obviously not that there are no energy dissipation losses. <br>
 +
There necessarily are other energy devaluating mechanisms that are not "friction". <br>
 +
While in thermally driven diffusion transport there is no "friction" the energy needs to be "expended" at the "pitstops" instead. <br>
 +
This is necessary in order to prevent reactions and diffusion transports to run backwards. <br>
 +
Related: [[Arrow of time]].
  
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For much more optimistic but less absolutely certainly on the safe side numbers there is work on coaxial carbon nanotubes:
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Stiff artificial nanosystems could be superior to soft nanosystems (natural and artificial) <br>
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Also in contrast to crystolecule bearings nanotube bearings are already somewhat accessible to experiments.
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because they may allow for more complete [[energy recuperation]] <br>
 +
using [[dissipation sharing]]. That is the "energetic change money" is not lost. <br>
  
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The following is from the paper: <br>
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Side-note: This only regards comparison of energy efficiency <br>
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"Evaluating the Friction of Rotary Joints in Molecular Machines"
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not comparison of maximal performances and operational ranges which both <br>
 +
are clearly vastly superior in stiff nanosystems.
  
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'''Assumed:'''
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== Macroscale friction ==
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* A nanotube bearing with 0.6nm radius and 5nm length
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* Bearing operating temperature: Roomtemperature 300K
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* Simulation was done at the rather high speed of 30m/s ~ 8GHz
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* P = 2.9(+-1.5)*10^-33 W/(rad/s)^2
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=== Classical friction ===
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Or converted into the same units as used in Nanosystems :
+
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* P = 7.25*10^-12 W/(m/s)^2
+
  
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For the above assumed 10^19 bearings this gives:
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There is classical friction with the friction coefficient µ. <br>
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* P = TODO
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Present e.g. in dry sliding sleeve bearings.
 +
* This type of friction is in first approximation independent of sliding (or rolling) speed
 +
* This type of friction is in first approximation independent of contact area
 +
* This type of friction is in dependent on normal force (load)
  
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= '''TODO''' update chapters below =
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=== Dynamic drag ===
  
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== The issue ==
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There is dynamic drag in liquids and gasses. <br>
 +
Present e.g. in hydrostatic and hydrodynamic bearings.
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* This type of friction is dependent on speed
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* This type of friction is dependent on contact area
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* there is dependence on normal force (load) but it requires an extended model.
  
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With shrinking size of machinery the surface area of this machinery rises.
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=== Macroscale bearings made form gemstone based nanomachinery ===
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Doubling the surface area doubles the friction (a [[scaling law]]).
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Extrapolating from speeds and friction levels of macroscale machinery leads to impractically high levels of waste heat generation.
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This is about the [[gemstone based metamaterial]] that is [[infinitesimal bearing]]s. <br>
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Distributing the speed difference over many layers can give low friction per bearing area even for higher speeds. <br>
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The rising total bearing interface are is overcompensated by the drop in friction from dropping speed. <br>
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Overall '''doubling the thickness of the stack of bearing layers halves the friction'''. <br>
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A inverse proportional linear relationship.
  
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This is one of the elephants in the room when introducing an audience to advanced APM.
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Practical bearings can have quite thin stacks of bearing layers. <br>
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Thin from the human scale perspective.
  
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Such an extrapolation is the first thing that any person knowledgeable in other micro- and nanotechnologies is likely do.
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'''Also related here is [[mesoscale friction]] and [[atomically precise roller gearbearing]]s.''' <br>
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Since this is not the only point where a first "quick" glance reveals a strongly discouraging result and experts usually are busy and have little time at hand to dig deeper, the situation sometimes leads these people to quickly deem all nanomachinery impossible, that looks superficially similar to macro scale cog-and-gear-machinery.
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Not roller bearings as friction may be too low for that. That is: Superlubricating rollers may slide rather than roll. <br>
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Going to [[atomically precise roller gearbearing]]s should lower friction quite a bit further judging from the per area friction loss levels of macroscale bearings. <br>
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Especially using micro-machionery (tech term: MEMS micro-electro-mechanical systems) as scaling trend leads to hugely misleading results.
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But it also introduces voids and larger runway surface area per bearing eventually reintroducing gradual wear e.g. by radiation hits. <br>
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Atomically tight seals still can prevent any and all gunk from getting in from the outside. So only internal seed-damage can self-amplify. <br>
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== What makes it work despite the issue ==
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Atomically tight seals need contact all around and thus remain a big contributor of friction. <br>
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Still they can be small in surface area compared to the gearbearings runway. <br>
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There are several effect working against this explosion of friction which are repeatedly overlooked.
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Runway only contributes to friction at and near the roller contacts. <br>
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'''Identifying a sweet spot for atomically precise gear-bearing size remains an open question.''' <br>
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=== Flawless surfaces drop friction significantly ===
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In contrast to etched micro-systems where the relative manufacturing error gets bigger with shrinking size.
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Atomically precise machinery has no error
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allow [[superlubrication]] which drops friction at least three orders of magnitude
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=== One needs to slow down anyway to prevent an explosion of productivity ===
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Rising productivity allows to slow down motion speeds (e.g. to just few mm per second) while keeping throughput constant.
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Slowing down to halve the speed drops drops the fiction to a fourth (a quadratic [[scaling law]] – tech term: dynamic drag).
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Main article: "[[Higher productivity of smaller machinery]]".
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=== Dropping speeds further by smart arrangements ===
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By dividing relative speeds up in several layers each taking a proportional part of the speed
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area goes up, yes, but the drop in speed has a bigger effect.
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See main article: "[[Infinitesimal bearing]]s"
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== Evolved molecular biology is not a proof that diffusion transport is the ideal solution with minimal losses ==
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With those aforementioned effects cog-and-gear nanomachinery could potential feature smaller losses than diffusion driven natural systems (more on that comparison further down). To quantify that more in depth investigations are needed.
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=== The issue ===
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Nature is often (probably mostly out of psychological reasons) seen as unsurpassable.
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But actually it is completely unknowable whether nature as a whole will be "surpassed" by artificial technology in the far future ([[nature vs technology|get side-tracked]]).  
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Regardless of that, specific aspects of nature definitively can (and have been) surpassed by artificial technologies
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(there are [[technology exceeding nature in performance|countless examples]]).
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Evolution ended up with diffusion transport and not cog-and-gear-machinery.
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Taken the former in to consideration that does by no means imply that this is the best or only solution.
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Actually evolution is facing severe [[Evolution#Limits_of_natural_evolution|limitations]] (lock-in-effect, incrementalism, ...).
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(This is only one of the many cases where [[misconceptions|bio-analogies]] can have a problematic effect on perception.)
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=== Why cog-and-gear transport may be more efficient ===
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While diffusion transport features no friction during the transport process itself
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diffusion transport is not at all lossless.
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At intermediate passing stations some energy always needs to be converted to heat (tech term: dissipated).
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Otherwise the chemical reactions would not have a preferred direction to go and all the molecular "machinery" would cease to do anything.
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Of course cog-and gear nanomachinery has exactly the same requirement.
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The big difference is that in biological systems energy often comes in discrete disconnected chunks.
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If ther's more than needed the excess is dissipated without being used for some desired effect.
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In a crude analogy it's like being unable to accept the change money.
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In cog-and-gear nanomachinery everything is linked together in one big [[machine phase]]
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There energy can be drawn in a continuous rather than discrete fashion.
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The dissipation necessary for forward moving operation (arrow of time) can be
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balanced and minimized further down to the absolutely unconditionally required minimum.  
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See main article: "[[Low speed efficiency limit]]"
+
  
 
== Related ==
 
== Related ==
  
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* [[Friction in gem-gum technology]]
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* '''[[Friction in gem-gum technology]]'''
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* [[Reciprocative friction in gem-gum technology]]
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* [[Friction in diffusion transport]]
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* '''[[Superlubricity]] reducing friction'''
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* [[How friction diminishes at the nanoscale]]
 
* [[Friction mechanisms]]
 
* [[Friction mechanisms]]
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* [[Superlubrication]] reducing friction
 
 
* [[Rising surface area]] causing more friction
 
* [[Rising surface area]] causing more friction
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* [[Macroscale style machinery at the nanoscale]]
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* [[Macroscale style machinery at the nanoscale]] – [[Common misconceptions about atomically precise manufacturing]]
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* [[Common misconceptions about atomically precise manufacturing]]
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* [[Feynman path]] – A naive form of scaling down saw blades and drills to the nanoscale (infeasible)
 
* [[Feynman path]] – A naive form of scaling down saw blades and drills to the nanoscale (infeasible)
 
* [[Pages with math]]
 
* [[Pages with math]]
 
* [[Evaluating the Friction of Rotary Joints in Molecular Machines (paper)]]
 
* [[Evaluating the Friction of Rotary Joints in Molecular Machines (paper)]]
 +
* '''[[Mesoscale friction]]'''
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----
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* [[Losses from mechanochemical reactions]]
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* '''[[Wear]]'''
  
 
[[Category:Pages with math]]
 
[[Category:Pages with math]]
Line 192: Line 136:
 
* Evidence of misconception: See section: "Fundamental Concepts" [https://en.wikipedia.org/w/index.php?title=Nanoelectronics&diff=775073056&oldid=770052236 Wikipedia: Nanoelectronics (2017-04-12)] (common false negatives).
 
* Evidence of misconception: See section: "Fundamental Concepts" [https://en.wikipedia.org/w/index.php?title=Nanoelectronics&diff=775073056&oldid=770052236 Wikipedia: Nanoelectronics (2017-04-12)] (common false negatives).
 
* [https://web.archive.org/web/20160322114752/http://metamodern.com/2009/02/10/nanomachines-how-the-videos-lie-to-scientists/ Nanomachines: How the Videos Lie to Scientists] ([[metamodern blog archive|Eric Drexlers metamodern blog]] (archive) 2009-02-10)
 
* [https://web.archive.org/web/20160322114752/http://metamodern.com/2009/02/10/nanomachines-how-the-videos-lie-to-scientists/ Nanomachines: How the Videos Lie to Scientists] ([[metamodern blog archive|Eric Drexlers metamodern blog]] (archive) 2009-02-10)
 +
 +
== Table of Contents ==
 +
 +
__TOC__

Latest revision as of 13:27, 1 April 2024

This page is meant to be a brief overview covering friction in …

Nanoscale friction

In gemstone metamaterial technology

Despite higher bearing surface area of smaller machinery
the friction in gem-gum technology stays manageable.

Friction not being a show-stopper is due to:

There are dissipation mechanisms that scale linear with speed but these are specific to reciprocative motions only.

(1) How nanomachineries innate high throughput density reduces friction

Higher throughput of smaller machinery leads to very little amount of nanomachinery needed
and thus to reasonably low bearing surface area within that.

(2) How the dynamic character of nanobearing friction can be exploited to reduce friction

Given quadratic gains in efficiency one wants to do a deliberate slowdown at the lower assembly levels where this type of friction is present.
Keeping throughput constant this means one needs to compensate for the loss of throughput with more nanomachinery.
More nanomachinery means a linear increase in losses. Quadratic gains times linear losses equals linear gains.
Overall linear gains in efficiency are still good and worth pursue.
See: Increasing bearing area to decrease friction

Recycle to reduce friction (not applicable to first time production)

Also a good design averts the need to disassemble things down to nanoscopic parts if
only larger scale reconfigurations are needed. – See: Convergent assembly
This kind of aversion of frictive losses only applies to recycling though.
Making recycling all the more desirable end economically viable. Nice!

Further reading

See main page: Friction in gem-gum technology This contains quantitaive estimations.

A bit more detailed but still brief exlanations to these effects/factors
can be found on the page How friction diminishes at the nanoscale.

In existing nanotechnologies

Stiff

  • Pretty much the only case where the above can already be experimentally tested (as of 2021) is in nested nanotubes and sliding graphene sheets.
  • At the microscale with MEMS there is the issue with stiction. Which may paint a misleading picture of how friction and wear scales when going down even further the sizescales.

Soft

It's hard to talk about friction is systems that are akin to biological cells.
It's obviously not that there are no energy dissipation losses.
There necessarily are other energy devaluating mechanisms that are not "friction".
While in thermally driven diffusion transport there is no "friction" the energy needs to be "expended" at the "pitstops" instead.
This is necessary in order to prevent reactions and diffusion transports to run backwards.
Related: Arrow of time.

Stiff artificial nanosystems could be superior to soft nanosystems (natural and artificial)
because they may allow for more complete energy recuperation
using dissipation sharing. That is the "energetic change money" is not lost.

Side-note: This only regards comparison of energy efficiency
not comparison of maximal performances and operational ranges which both
are clearly vastly superior in stiff nanosystems.

Macroscale friction

Classical friction

There is classical friction with the friction coefficient µ.
Present e.g. in dry sliding sleeve bearings.

  • This type of friction is in first approximation independent of sliding (or rolling) speed
  • This type of friction is in first approximation independent of contact area
  • This type of friction is in dependent on normal force (load)

Dynamic drag

There is dynamic drag in liquids and gasses.
Present e.g. in hydrostatic and hydrodynamic bearings.

  • This type of friction is dependent on speed
  • This type of friction is dependent on contact area
  • there is dependence on normal force (load) but it requires an extended model.

Macroscale bearings made form gemstone based nanomachinery

This is about the gemstone based metamaterial that is infinitesimal bearings.
Distributing the speed difference over many layers can give low friction per bearing area even for higher speeds.
The rising total bearing interface are is overcompensated by the drop in friction from dropping speed.
Overall doubling the thickness of the stack of bearing layers halves the friction.
A inverse proportional linear relationship.

Practical bearings can have quite thin stacks of bearing layers.
Thin from the human scale perspective.

Also related here is mesoscale friction and atomically precise roller gearbearings.
Not roller bearings as friction may be too low for that. That is: Superlubricating rollers may slide rather than roll.
Going to atomically precise roller gearbearings should lower friction quite a bit further judging from the per area friction loss levels of macroscale bearings.
But it also introduces voids and larger runway surface area per bearing eventually reintroducing gradual wear e.g. by radiation hits.
Atomically tight seals still can prevent any and all gunk from getting in from the outside. So only internal seed-damage can self-amplify.
Atomically tight seals need contact all around and thus remain a big contributor of friction.
Still they can be small in surface area compared to the gearbearings runway.
Runway only contributes to friction at and near the roller contacts.
Identifying a sweet spot for atomically precise gear-bearing size remains an open question.

Related

External links

Table of Contents

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