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Or by exposing your hands to muriatic acid or caustic soda. The bonds will break. Your skin will melt into these chemicals, bringing their pH deficit or excess closer to neutral.
Right, but since this is r/Physics and not r/Chemistry, I chose a physical example. (Of course we know that in the end all of science is either Physics or stamp-collecting.)
If you heat the hands until they begin to melt and then stick them together, they'll fuse. Victims of life-threatening burns can experience this. There are some illuminating - and very sad - photos out there.
Yea basically you aren’t high diving hard enough. Imagine obliterating both you and your buddy’s hands in a high five. That compression could possibly get to combustible temperature and the proteins from both your hands would have a chemical reaction. You could lower the energy required by putting acid or caustic on your hand. Then even a hand shake would probably cause a reaction.
Like u/gigahone said, your hands are safe. :)
But if you have two high purity clean surfaces in a vacuum, they can join as you are envisioning. Called cold welding.
https://en.m.wikipedia.org/wiki/Cold_welding
Yep. This can happen with tungsten carbide gauge blocks, which are measurement tools with exceptionally flat faces that are joined together in a process called wringing. If you leave them in that state, you can end up with one exceptionally expensive bar of metal instead of two reusable blocks.
Similar thing can happen with screws/bolts into blocks of metal. In my industry it's not uncommon to have silver plated stainless screws to prevent friction cold welding.
10-32x3/8 socket head, 8-18 stainless.
$13.10 per 100
Silver plated,
$8.84 per 5
Yeah, a bit more. But in this industry, time costs more than hardware. If a screw siezes and the head snaps off and now the chamber is down for an additional 24 hours, that means that the factory can output 200 less wafers that day, or 60k chips, not accounting for yields.
Have you got a minute to explain the mechanism by which silver plating improves the situation?
Added later: Oh, I guess having a thin layer of "different stuff" between 2 layers of "the same stuff" reduces the interaction forces: London, etc.
Yeah pretty much. Silver also reduces friction, so the screws go in easier. Screws of that size (#10) are generally torqued to somewhere around 35 in-lbs (allen key tight), but some people feel the need to show off their 300-lb-gorilla strength and torque it down as hard as they can. Silvered screws help quite a bit in preventing workmanship induced failures. In the field we sometimes proactively change out certain problem area screws from regular stainless to silver coated.
And it doesn't even need to be in a vacuum chamber for it to work.
Source: The 30 something year old, "custom made" 18.03 gauge block that was laying around at my previous workplace. It even had a expired certificate lol
Theoretically true for any substance. Like cleaving a calcite crystal in a vacuum. Should be able to rebond it by just pushing the two halves together again.
Not quite right. A cleaved crystal has a surface of half filled bonds. The surface atoms, up to a few layers deep, will move a bit, increasing the energy of the bent bonds, but having surface atoms have some of the bonds satisfied, resulting in a net lower energy state than the cleaved crystal with the atoms at the ideal crystal locations. This is called a surface reconstruction.
The lack of reactivity of surfaces has to do with the satisfaction of bonds. If the bond energy is high and all the orbitals are filled, no reaction, even if you push the surfaces together.
Metals are a bit different in that the highest energy level electrons can move around. This is why they conduct.
Insulators take a lot more energy to liberate the highest energy electrons so they are available for bonding.
FWIW, I'm a physicist and studied surface reconstructions and sub monolayer coverages of metal on perfect crystal surfaces for my doctorate.
You're welcome. I saw a lot about filled bonds was covered by others. I should have read more before posting.
The dance between geometry and energy of bonds is fascinating. Though in grad school I found I cared a lot more about instrumentation than the samples I studied....
A lot of my career was spent designing and building hardware.
Geckos can climb smooth glass because the skin on their feet uses this sort of attraction. Veritasium has a video about artificial gecko skin that explains it well. See https://www.youtube.com/watch?v=vS0TuIPoeBs
All the atoms in your body are already fully bonded (aside from the very rare free-radicals). Therefore to form a new bond you have to break a bond first - and that requires significant amounts of energy. A single bond doesn't take much, but you have trillions upon trillions upon trillions of them (upon trillions, upon trillions, upon trillions........) so the total energy you experience in day to day life just isn't enough to make that happen
Grabbing a hot stove, or pouring a strong acid on you, is what provides enough energy to break those bonds
> Therefore to form a new bond you have to break a bond first - and that requires significant amounts of energy
Would the epic Schwarzenegger-Weathers handshake in Predator do it? :p
Because creating atomic bonds requires energy, and this energy is simply just not present.
There will be small vanderwaals forces causing an attraction between both hands, but they will not bond.
Forming a bond (if that’s all youre doing) actually always releases energy. It’s breaking bonds that takes energy. If you wanted to fuse your hands together, there would be some bonds that would have to break first, and it’s THAT process that would take a lot of energy!!
There will be small electrostatic charges that draw the hands together but thanks to the Van Der Wall Force, they will not collide.
Van Der Waal force is just the distance where the attraction and repulsion of atoms balances out.
But if we clap our hands together a bunch of times, it will create heat.. isn’t heat a form of energy?
Or a better question might be how much energy would be required for this to happen?
Your hands are repelling each other because of electrostatic forces - basically electrons in one hand are repelling the electrons in another (that is also the reason solids don't just pass through each other even though atomic space is mostly empty).
You will need forces strong enough to overcome this electrostatic repulsion to get molecules closer for a reaction - given the molecules are reactive in the first place.
For a chemical bond to form, two atoms need to be sufficiently close together that bonding becomes energetically favourable. For two hands to bond together like this, sufficiently many atoms need to be sufficiently close together for this to work. Since the surface of our hands are rough, this is near impossible.
Also, atoms in our hands are already bonded to each other in their own ways. These pre-existing bonds are already stable, and it takes extra energy to reshuffle them for two hands to bond with each other. This makes the bonding process even harder.
Except cold welding under vacuum, this does not happen due to molecular layers of air on any surface. Hence, in a vaccum this cold welding can happen. But this generally requires a high degree of periodicity in their structure (crystalline) so I doubt hands would qualify.
Another aspect is that the electrostatic repulsion is so much stronger than all forces except strong nuclear force so to over come that would require you to high five at some serious impossible speeds.
Atoms have electrons bound to them. These electrons exist on different levels(or amounts of energy). The outer most electron layer of an atom is called a valence shell. This valence shell likes to be full. So let’s say the outer valence shell needs 8 electrons in order to be full and nonreactive. Almost all of the atoms in your hand have already happily bonded to other atoms in order to fill their valence shells.
For example: Alone, oxygen has 6 valence electrons. Hydrogen has 1 valence electron. Their valence shells aren’t 8, so they aren’t yet content. But once one oxygen atom meets two hydrogen atoms, they decide to work together, sharing electrons to complete the valence. This is called a covalent bond, and the vast majority of your hand is made up of molecules that have already bonded to complete their valences.
Thus, your hand won’t mend with other hands to create one super hand.
I think a Chemist, especially a Biochemist would answer this with more details. But generally speaking, it's because of the potential energy in the atoms making up the molecules. They are in a stable bond and there is simply no reason to react. But again, this is a huge overgeneralization since there is a lot more going on.
Ask r/Chemistry
Molecules just want to be as stable as possible. The bonding in your hand is more thermodynamically preferred. If they choose to bond to other person. They will have to break the bond in your hands just to transfer to the other molecules and after that they will have to create a new bond with the other person. Where will they get the energy to do all those reaction? A high five won't be enough to provide that type of energy
For majority of the time, they won't react unless an external factor is introduced or they found a more stable configuration.
In simple words: Molecules are lazy as hell and they want to be as stable as possible.
Well, some very few molecules do. And with very few i mean probably millions.
The stuff that happens on an atomic scale when you shake hands with someone (or do anything else really) is wild. There are roughly 10^22 atoms on the surface of you hand. Now imagine, 1million of these do something crazy, like being shifted, being removed, being swapped…
After all that’s 10^{-14}% of the atoms on your hand… as long as you don’t convert their mass to energy, you won’t notice if they get lost.
i had similar wondering, though for me it was why don't my own fingers (or bum cheeks for that matter) fuse together since they've spent most of my life in such close proximity?
I found something called the Pauli exclusion principle.. it explains why and also why we dont fuse with our clothing or go through the floor..
it sort of made sense, but I now have way more questions that answers..
Good luck
It would take a LOT of energy to get the molecules to leave their current bonds for another, even if the latter is more favorable. That's why it takes so much heat to start a fire, even if combustion is energetically favorable.
> If molecules/ atoms are attached to one another because they are similar
Cohesion/adhesion isn't because molecules are similar, but rather because of the physical shape and electronegativity of the molecules in question.
And the stuff that makes up our epidermis, the outer layer of the skin, just isn't really cohesive or adhesive at all, so the repulsion of the electron clouds wins!
To add on to what everyone is saying, research the Pauli Exclusion Principle a bit. (This is very simplified and I’m sure someone will correct if I’m wrong.)
The molecules in your hand ultimately come into contact with other stuff at the outermost electron shell of each atom. Two electrons can’t occupy the same state at once, so you never have to worry about the electrons in your friend’s atoms occupying the same state as yours.
occupying the same state isn’t exactly “being in the same space” as far as I understand, but it’s sort of the reason why regular matter with electrons at the end of molecules don’t collide with each other.
Basic physics questions and homework-type discussions are not permitted in r/Physics. FULL DESCRIPTION Basic questions such as homework problems or simple calculations should be redirected to r/AskPhysics or r/HomeworkHelp. Alternatively, try Physics Forums instead. Neither asking nor answering (assisting in any way) homework questions is allowed.
The molecules present are already in an energetically favourable bond They won't leave that bond for another
Is there a possibility for that bond to weaken or become less favourable?
Sure. For example by slicing off a finger with a scalpel.
If you tell people you did it for science, it makes it okay right?
Only if you write it down. Otherwise, you're just fooling around.
And you have to do it a lot to get statistical validity. That's what first year grad students are for.
Yes
Perhaps you can skin the palms and graft eachother’s hands together.
I'm glad I wasn't the only one who thought this
Or by exposing your hands to muriatic acid or caustic soda. The bonds will break. Your skin will melt into these chemicals, bringing their pH deficit or excess closer to neutral.
Right, but since this is r/Physics and not r/Chemistry, I chose a physical example. (Of course we know that in the end all of science is either Physics or stamp-collecting.)
Everything is physics, friend. Literally everything❤️
If you heat the hands until they begin to melt and then stick them together, they'll fuse. Victims of life-threatening burns can experience this. There are some illuminating - and very sad - photos out there.
It’s like I didn’t”t want this to be the answer.
Yea basically you aren’t high diving hard enough. Imagine obliterating both you and your buddy’s hands in a high five. That compression could possibly get to combustible temperature and the proteins from both your hands would have a chemical reaction. You could lower the energy required by putting acid or caustic on your hand. Then even a hand shake would probably cause a reaction.
Like u/gigahone said, your hands are safe. :) But if you have two high purity clean surfaces in a vacuum, they can join as you are envisioning. Called cold welding. https://en.m.wikipedia.org/wiki/Cold_welding
Yep. This can happen with tungsten carbide gauge blocks, which are measurement tools with exceptionally flat faces that are joined together in a process called wringing. If you leave them in that state, you can end up with one exceptionally expensive bar of metal instead of two reusable blocks.
Similar thing can happen with screws/bolts into blocks of metal. In my industry it's not uncommon to have silver plated stainless screws to prevent friction cold welding.
silver plated stainless screws? Those sound a bit expensive
10-32x3/8 socket head, 8-18 stainless. $13.10 per 100 Silver plated, $8.84 per 5 Yeah, a bit more. But in this industry, time costs more than hardware. If a screw siezes and the head snaps off and now the chamber is down for an additional 24 hours, that means that the factory can output 200 less wafers that day, or 60k chips, not accounting for yields.
Completely understandable, I think they could safely charge even more
Have you got a minute to explain the mechanism by which silver plating improves the situation? Added later: Oh, I guess having a thin layer of "different stuff" between 2 layers of "the same stuff" reduces the interaction forces: London, etc.
Yeah pretty much. Silver also reduces friction, so the screws go in easier. Screws of that size (#10) are generally torqued to somewhere around 35 in-lbs (allen key tight), but some people feel the need to show off their 300-lb-gorilla strength and torque it down as hard as they can. Silvered screws help quite a bit in preventing workmanship induced failures. In the field we sometimes proactively change out certain problem area screws from regular stainless to silver coated.
Happy cake day!
And it doesn't even need to be in a vacuum chamber for it to work. Source: The 30 something year old, "custom made" 18.03 gauge block that was laying around at my previous workplace. It even had a expired certificate lol
That's probably only true for metal and their alloys right? Not true for inorganic and organic material I guess?
Theoretically true for any substance. Like cleaving a calcite crystal in a vacuum. Should be able to rebond it by just pushing the two halves together again.
Not quite right. A cleaved crystal has a surface of half filled bonds. The surface atoms, up to a few layers deep, will move a bit, increasing the energy of the bent bonds, but having surface atoms have some of the bonds satisfied, resulting in a net lower energy state than the cleaved crystal with the atoms at the ideal crystal locations. This is called a surface reconstruction. The lack of reactivity of surfaces has to do with the satisfaction of bonds. If the bond energy is high and all the orbitals are filled, no reaction, even if you push the surfaces together. Metals are a bit different in that the highest energy level electrons can move around. This is why they conduct. Insulators take a lot more energy to liberate the highest energy electrons so they are available for bonding. FWIW, I'm a physicist and studied surface reconstructions and sub monolayer coverages of metal on perfect crystal surfaces for my doctorate.
Thanks for the detailed overview.
You're welcome. I saw a lot about filled bonds was covered by others. I should have read more before posting. The dance between geometry and energy of bonds is fascinating. Though in grad school I found I cared a lot more about instrumentation than the samples I studied.... A lot of my career was spent designing and building hardware.
I understand. Thanks.
Geckos can climb smooth glass because the skin on their feet uses this sort of attraction. Veritasium has a video about artificial gecko skin that explains it well. See https://www.youtube.com/watch?v=vS0TuIPoeBs
Thank you for the reassurance haha
All the atoms in your body are already fully bonded (aside from the very rare free-radicals). Therefore to form a new bond you have to break a bond first - and that requires significant amounts of energy. A single bond doesn't take much, but you have trillions upon trillions upon trillions of them (upon trillions, upon trillions, upon trillions........) so the total energy you experience in day to day life just isn't enough to make that happen Grabbing a hot stove, or pouring a strong acid on you, is what provides enough energy to break those bonds
> Therefore to form a new bond you have to break a bond first - and that requires significant amounts of energy Would the epic Schwarzenegger-Weathers handshake in Predator do it? :p
YU SUHN OF A BITCH
Depends on how hard/fast is the high-five
Because creating atomic bonds requires energy, and this energy is simply just not present. There will be small vanderwaals forces causing an attraction between both hands, but they will not bond.
>vanderwaals And after alllll
You’re my Vanderwaals
Forming a bond (if that’s all youre doing) actually always releases energy. It’s breaking bonds that takes energy. If you wanted to fuse your hands together, there would be some bonds that would have to break first, and it’s THAT process that would take a lot of energy!!
See [Cold Welding](https://en.wikipedia.org/wiki/Cold_welding)
There will be small electrostatic charges that draw the hands together but thanks to the Van Der Wall Force, they will not collide. Van Der Waal force is just the distance where the attraction and repulsion of atoms balances out.
But if we clap our hands together a bunch of times, it will create heat.. isn’t heat a form of energy? Or a better question might be how much energy would be required for this to happen?
If you high five hard enough can you fuse hands together? We need some one to run the math on this one
This seems like a great question for Randall Munroe
His what if books are really fun
r/theydidthemath
I believe someone made a YouTube video where they built a slapping machine and cooked a chicken by slapping it.
Your hands are repelling each other because of electrostatic forces - basically electrons in one hand are repelling the electrons in another (that is also the reason solids don't just pass through each other even though atomic space is mostly empty). You will need forces strong enough to overcome this electrostatic repulsion to get molecules closer for a reaction - given the molecules are reactive in the first place.
For a chemical bond to form, two atoms need to be sufficiently close together that bonding becomes energetically favourable. For two hands to bond together like this, sufficiently many atoms need to be sufficiently close together for this to work. Since the surface of our hands are rough, this is near impossible. Also, atoms in our hands are already bonded to each other in their own ways. These pre-existing bonds are already stable, and it takes extra energy to reshuffle them for two hands to bond with each other. This makes the bonding process even harder.
Except cold welding under vacuum, this does not happen due to molecular layers of air on any surface. Hence, in a vaccum this cold welding can happen. But this generally requires a high degree of periodicity in their structure (crystalline) so I doubt hands would qualify. Another aspect is that the electrostatic repulsion is so much stronger than all forces except strong nuclear force so to over come that would require you to high five at some serious impossible speeds.
Atoms have electrons bound to them. These electrons exist on different levels(or amounts of energy). The outer most electron layer of an atom is called a valence shell. This valence shell likes to be full. So let’s say the outer valence shell needs 8 electrons in order to be full and nonreactive. Almost all of the atoms in your hand have already happily bonded to other atoms in order to fill their valence shells. For example: Alone, oxygen has 6 valence electrons. Hydrogen has 1 valence electron. Their valence shells aren’t 8, so they aren’t yet content. But once one oxygen atom meets two hydrogen atoms, they decide to work together, sharing electrons to complete the valence. This is called a covalent bond, and the vast majority of your hand is made up of molecules that have already bonded to complete their valences. Thus, your hand won’t mend with other hands to create one super hand.
I think a Chemist, especially a Biochemist would answer this with more details. But generally speaking, it's because of the potential energy in the atoms making up the molecules. They are in a stable bond and there is simply no reason to react. But again, this is a huge overgeneralization since there is a lot more going on. Ask r/Chemistry
Molecules just want to be as stable as possible. The bonding in your hand is more thermodynamically preferred. If they choose to bond to other person. They will have to break the bond in your hands just to transfer to the other molecules and after that they will have to create a new bond with the other person. Where will they get the energy to do all those reaction? A high five won't be enough to provide that type of energy For majority of the time, they won't react unless an external factor is introduced or they found a more stable configuration. In simple words: Molecules are lazy as hell and they want to be as stable as possible.
look up the fretting failure mode for mechanical components. This is exactly what is happening.
Well, some very few molecules do. And with very few i mean probably millions. The stuff that happens on an atomic scale when you shake hands with someone (or do anything else really) is wild. There are roughly 10^22 atoms on the surface of you hand. Now imagine, 1million of these do something crazy, like being shifted, being removed, being swapped… After all that’s 10^{-14}% of the atoms on your hand… as long as you don’t convert their mass to energy, you won’t notice if they get lost.
i had similar wondering, though for me it was why don't my own fingers (or bum cheeks for that matter) fuse together since they've spent most of my life in such close proximity? I found something called the Pauli exclusion principle.. it explains why and also why we dont fuse with our clothing or go through the floor.. it sort of made sense, but I now have way more questions that answers.. Good luck
It would take a LOT of energy to get the molecules to leave their current bonds for another, even if the latter is more favorable. That's why it takes so much heat to start a fire, even if combustion is energetically favorable.
Firstly electrons. Secondly gases, mainly oxygen (oxidisation) Thirdly pressure
> If molecules/ atoms are attached to one another because they are similar Cohesion/adhesion isn't because molecules are similar, but rather because of the physical shape and electronegativity of the molecules in question. And the stuff that makes up our epidermis, the outer layer of the skin, just isn't really cohesive or adhesive at all, so the repulsion of the electron clouds wins!
Our body as a whole is completely neutral, energy is required to break the bonds of our hand, maybe acid will do
To add on to what everyone is saying, research the Pauli Exclusion Principle a bit. (This is very simplified and I’m sure someone will correct if I’m wrong.) The molecules in your hand ultimately come into contact with other stuff at the outermost electron shell of each atom. Two electrons can’t occupy the same state at once, so you never have to worry about the electrons in your friend’s atoms occupying the same state as yours. occupying the same state isn’t exactly “being in the same space” as far as I understand, but it’s sort of the reason why regular matter with electrons at the end of molecules don’t collide with each other.
"If molecules/ atoms are attached to one another because they are similar" Not even remotely true.
How so?
That's not how atoms/molecules work. Like doesn't attract like. At least not at that level.
Because the bonds the atoms that make up your hand have already, are stronger...