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What actually happens when two masses touch each other?

  1. Aug 14, 2007 #1
    When I clap my hands, the electrons or the nucleus on my hands are not touching each other, right? The protons on both the hands need to repel, and same thing with the electrons. If my hands (or anything in the universe, unless tremendous force is applied on them) are not touching each other, how am I getting the touch sense?

    Thanks,
    .joby
     
  2. jcsd
  3. Aug 14, 2007 #2

    G01

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    When you "feel" something, what you are actually sensing is the repulsive force between your fingers and whatever your touching. This is all the touch sense is. In fact, without this repulsive force, you wouldn't be able to feel anything since you'd pass right through what you were trying to feel!
     
    Last edited: Aug 14, 2007
  4. Aug 14, 2007 #3
    You have pressure sensitive neurons in your skin that relay an electrical signal to the brain. When you bring the electrons in your hand in close proximity to your skin, the electrons on the skin experience a pressure (the magnitude of which depends on how close the electrons are pushed together and over what area). The neurons react and can transmit this signal into an electrical impulse that is sent to the brain. People who have damaged their nerve cells in the skin cannot relay the signal to the brain, and hence the lose the sensation of "touch" in that part of their body. For example, I am sure you have seen somewhere someone hit a hammer against someone with a paralyzed leg and they have no reaction or feeling of the contact. The electrons in the hammer still push up against the electrons in the leg, but the sensation of "feeling" is not there in this case because the mechanism that creates that sensation has been damaged.
     
  5. Aug 14, 2007 #4
    When a lightning hits a lightning protector (that metal rod that we keep on top of the tall buildings to protect from the lightning; don't know the actual name), it conducts the electrons to the earth. But if I hit the lightning protector with a hammer, it just breaks. Why? Shouldn't it just conduct the electrons from the hammer to the earth?
     
  6. Aug 14, 2007 #5

    jtbell

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    A hammer is normally electrically neutral. If you try to remove more than a minuscule number of electrons from the hammer, the extra protons left behind immediately pull them back again.

    However, if you charge up the hammer beforehand with an excess of electrons, then when you touch it to a lightning rod those electrons will flow into the rod and down into the ground, leaving the hammer electrically neutral.
     
    Last edited: Aug 14, 2007
  7. Aug 14, 2007 #6

    Claude Bile

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    In a collision between two bodies, the repulsive force that is felt is far more dependent on the interatomic bonds between the atomic nucleii that constitute the solids rather than the electrons. That is why a gas does not repel the motion of your hand as effective as a table.

    Claude.
     
  8. Aug 14, 2007 #7
    I think the OP might be asking why do those gas atoms bounce away from your hand, rather than passing straight through?

    Isn't the answer all to do with tightly-bound electrons? If each atoms electrons are bound to remain in a cloud around the respective nucleus (at the very bottom of their energy well), then much more energy (i.e., work) will be needed to bring two nuclei anywhere close together (because proximity requires overlap between clouds of many mutually repulsive electrons, and possibly also redistributes electrons to be further from the nuclei). On the other hand, free electrons are the seldom few which already have so much energy as to be able to escape the potential well of their original atom (and be conducted elsewhere).
     
    Last edited: Aug 14, 2007
  9. Aug 15, 2007 #8

    DaveC426913

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    Are you forgetting that the hammer is made of atoms, not simply electrons?

    P.S. The metal rod lightning procector you speak of is refered to by the cryptic name "lightning rod".
     
  10. Aug 15, 2007 #9

    Danger

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    I'm getting confused my own self, Claude. Cesiumfrog's description is in line with my (albeit limited) education. Can you elaborate upon your response?
     
  11. Aug 15, 2007 #10
    Alright. Thinking further on these topics, the mechanical strength is mostly based on the interatomic strength. The electric conductance of a material is based on how loosely the electrons attached to the nucleus of an atom. That explains why plastic is an insulator, but it is not strong as iron. And iron is strong, but it conducts electricity.

    In my imagination, electricity conducts as follows:

    An electron mechanically moves in one direction. That causes the neighbouring electron to repel and the neighbouring electron also start moving in the same direction. Eventually it becomes a flow of electrons and we call it electric current.

    If the above logic is true, let me rephrase my original lightning rod question. When I hit the lightning rod with an iron hammer with tremendous force, the electrons in the surface of the hammer are coming closer to the lightning rod electrons. This should cause the electrons in the lightning rod to repel and an electric current should be generated. Right?
     
  12. Aug 15, 2007 #11

    Danger

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    No. You're correct that the electrons in the rod repel the electrons in the hammer (although Claude's post sort of modifies that). The point, though, is that there's no transfer of electrons, unless there's some minor static charge on one or the other, which is insignificant.
    One thing that you might note from whapping a rod with a hammer, though, is that the rod might become magnetized if it's made of ferrous material.
     
  13. Aug 15, 2007 #12

    Claude Bile

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    My post was made with macroscopic objects in mind. While electronic repulsion prevents things from passing through one another, the macroscopic force (or impact if you like) that we might associate with something like clapping, or hitting a lightning rod with a hammer is dependent on the interatomic forces within the colliding bodies.

    Claude.
     
  14. Aug 15, 2007 #13

    Danger

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    Oh... I was unaware of that, but it makes sense now that it's been pointed out. Thanks.
     
  15. Aug 15, 2007 #14

    jtbell

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    So are the (positively charged) nuclei at the surface of the hammer.

    The nuclei at the surface of the hammer also attract the electrons in the lightning rod with an equal but opposite force, so there is no net force on the electrons in the rod.
     
  16. Oct 1, 2008 #15
    Maybe I can clear some things up.

    I believe electric current flows like this
    You have a Positive potential and a Negative potential. Atoms seek to have a neutral charge.....So when you take a valence electron from an atom....it becomes positively ionized.....So the charge of the atom is positive, making it ready for another electron. With enough voltage(potential energy).... you'll have another electron enter that "exciton" left by the previous electron that was in the cloud around the nuclei. And so and so goes for each atom in the traveling medium. That's why copper conducts so well.....it has one valence electron so it has plenty of room for sharing in a bonded material and doesn't take much energy for its electron to reach the conduction band.
     
  17. Oct 1, 2008 #16
    sure if your hammer is a strong negative potential. Like lightening is.

    Remember

    Negative to Positive is the flow of electrons.
     
  18. Oct 1, 2008 #17
    No, the electrons will transfer if they're attracted by a positive potential.
    Therefore if the atom is neutrally charged..... then the electrons would just repel any other contact with electrons...not be knocked out of the electron cloud into another atoms electron cloud. Although that does happen on some occasions. Whenever you have enough VOLTAGE a electron can and will knock some other electrons out.... This happens in semiconductors with a pn junction. It's called the "Avalanche Effect/Breakdown" Whenever you reverse bias a semiconductor.
     
  19. Oct 31, 2008 #18
    Newbie question...

    Is there ANY space at the point of singularity? Any space between any of the known type of particles, or is everything (energy, matter, photons, quark, muon, boson, etc... anything and everything in existance) squashed into a single point less any open space?
    Is this the picture of pre big bang? If so there would be no speed of light, correct? Speed of light would not exist until space was introduced into the equation. Is that correct? I believe relativity states gravity is the warping of time and space. Could it be argued that gravity is the lack of space and time? Any and all feedback is appreciated.
    Thanks
     
  20. Oct 31, 2008 #19
    In metals is a quite different situation.
    There are some "collective" or free electrons that do not belong to any atom in particular. As you said, the atomic cores will be ionized (positive) and the free electrons will move almost freely through the lattice of positive ions. They don't hop from atom to a atom (they may do this in some semiconductors).
    When an external electric field is applied, these free electrons will have some general trend to move from negative to positive (they also have the random thermal motion)

    Note: The electrons in metal are (almost) free to move in the metal but they are nor free to leave the metal. It takes considerable energy to extract electrons from the metal (of the order of few electronVolts per electron).

    Regarding the main topic:

    When you hit two metals it's not impossible to transfer few electrons. But why do you think they will go from the hammer to the lighting rod and not the other way around? Or both ways? And you don't actually have to hit. When you put two metals in contact there is a transfer of electrons (for a very short time) until an equilibrium is reached.
     
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