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Whats the point particle energy due to its referance frame ?

  1. Jul 11, 2015 #1
    Lets suppose we have infinitly small particle.And we want to measure the kinetic and potantial energy of particle.Can we use the particle itself a referance frame to calculate this energy ? To clarify my question lets suppose the point position shown by P point and its P(x,y,z) then we want to measure kinetic energy due to the referance frame which the referance frame point F is;F(x,y,z)

    Is this possible ?
    If its possible do we get zero ?
    Or we get ##mc^2##
  2. jcsd
  3. Jul 11, 2015 #2
    With regards to kinetic energy, it is not dependent upon size only mass:


    The potential energy however would be dependent upon what model you place it in. Potential for what? Now if we are talking gravity, then it would depend on if the pariticle had mass. If it does have mass and it is infinitely small, then we get into the same problems everyone has with black holes. Depending on your theoretical view of the Plank Constant, you either have an infinite potential energy, or we state that the particle is of finite size due to the lower limits of size within the space time manifold of our universe.
  4. Jul 11, 2015 #3
    What do you mean ?, in it's own reference frame the particle is at rest !, When you are in a car, you never see it moving, because you are moving with it and it velocity will become 0 (in your frame) so you should expect no kinetic energy but you'll be able to measure it's potential energy (because fields transform when you move from a frame to the other), but even though an infinitesimally small particle would rather obey a quantum mechanical law (quantum in action), and the particle's "frame" isn't well defined, you don't even sure about were it it, but even if you weren't at that frame, the particle's energy E will appear in discrete quantities every time and you can't really decide what's the particle energy and there is also uncertainty that depend on the time you measure it's energy, so talking the particle's frame will make things impossibly complicated !
  5. Jul 11, 2015 #4
    In your statement you said there was a particle infinitely small and no reference to any other object. With your example of a car, you are giving reference to the it moving presumably against the ground. So you have the mass of the car verse the mass of the planet to which you have potential energy of the gravity between the two. So a particle at rest with no other object in reference to react with has zero potential energy. It can only have energy in relation to another object, not space itself.
  6. Jul 11, 2015 #5
    This is my idea theres no other object to effect this particle.

    Now you claimed that potantial energy is zero.

    For about mass think electron.Its Infinitly small but it has mass.

    What will happen kinetic energy ?
  7. Jul 11, 2015 #6
  8. Jul 11, 2015 #7
    What that suppose to mean I well defined it with position.Is there anything to add ?
    And I dont think this question needs QM.Well you cant detect particles position exactly in realty but for simplicity lets assume this not true.Or lets assume you are in room (you are in or outside the room its not matter)Now think this room is in exist infinte universe.So at some point we can think this room is infinitly small.Think this way.
  9. Jul 11, 2015 #8
    Are you trying to say when we change the size of electron we are changing our answer?
  10. Jul 11, 2015 #9


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    Science Advisor

    No, no one has claimed that the potential energy is zero. What you have been told several times here is that the potential energy of an object depends upon the frame of reference. Given any particle in the universe, there exist a frame of reference in which its potential energy is 0 and another in which it is what ever value you wish.

    But the size of an object, as opposed to its mass, has nothing to do with either potential or kinetic energy.

    "What will happen to kinetic energy" when what happens?
  11. Jul 11, 2015 #10
    Here my idea kinetic energy is zero Why cause kinetic energy is ##W=∫Fdx## here theres no change in position so its zero.For potantial energy same thing ##W=-∫Fdx## so theres no change in potantial energy so again zero.
    Whats wrong with this ?

    Here the main problem is referance frame and particle is same place.Is something like this possible in physics ? Thats my question from the begining.You answered yes I guess but I am not sure.If you answered yes then I need to move my next question.
  12. Jul 11, 2015 #11
    One thing for sure is that kinetic energy is zero, and there maybe be a potential of any kind, a good example would be an electron in a conducting wire, or an electron in the earth's gravitational field, if you try to do the expirement, you'll not be able to do it, because you simply can't find an electron and be in it's reference frame, this is purely theoretical and thus many answers should arise, but you'll never know for sure !!
  13. Jul 11, 2015 #12
    For your first question answe look #4 post.And I have already give the referance frame.

    You second statment.I know size does not affect anything but here you guys didnt undstand the conceot of inifintly small I guess.So I am trying to explain here my ideas.

    Third statement ask when.Here theres no importance of time.Its not relevant with my question.

    Please post If you know something about this issue.
  14. Jul 11, 2015 #13
    I understand.Hmm You said you will never know.Is that a problem for physics rules ? Is that violates anything ? Or Is this is a not preferred referance frame ? Isnt it
  15. Jul 11, 2015 #14
    The problem is the object is real small, quantum mechanics is in action and you won't know anything for sure, that is the REAL world and what's REALLY happening, and doing that expirement is almost impossible, and before doing and expirement you can't know, the most difficult part is taking the particle's frame of reference, and that's impossible to do without messing the particle state (also changing her energy),
  16. Jul 11, 2015 #15
    Here the thing.I give electron example to visualise the idea.Let suppose you are looking 13 billion away galaxy.You will see it so so small even like a electron.Size is relative thing.Electron is so small for US.But not for an another electron.Here the important thing.If you look further and observe a so small object and size is like electron size.
    This time can you say this galaxy obeys QM.
    If your answer is yes no problem.But your answer is no.Then you should consider your answer again cause I am not talking about electron.I am talking about huge objects.What will happen when I see a galaxy (its so far which its radius or size is like an electron due to us)What will happen the referance frame and kinetic energy ? Theres again a problem ?

    And I need a really answer to this question : Is this is a not preferred referance frame ?
  17. Jul 11, 2015 #16
    What you are saying are thought expirements, can you do the expirement? ,well a straight forward answer will be No kinetic energy but potential energy may arise, but you can't do the expirement(extremely hard), and if you look at a galaxy and see something happen, it has happend millions of years ago, It's already been decided so you can't really know if they do obey quantum mechanics from your reference (of course, this is purely theoretical), come up with an expirement and blow my mind !!!,
    Last edited: Jul 11, 2015
  18. Jul 11, 2015 #17
    I am University first grade.Maybe later of my academic career
  19. Jul 11, 2015 #18


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    Science Advisor

    No. Using the particle's reference frame means we define our coordinate system so that the electron is not moving within that coordinate system. Since the particle isn't moving, it's velocity is zero and so is its kinetic energy.

    To define potential energy, you need two points. One for the particle's position, and one for the position you are defining the potential energy against. Since the change in potential energy ΔU is given by the equation ΔU = -W, where W is the work performed on the particle to move it between the two points, setting both of your points the same means no work is done to the particle and the potential energy is zero. In other words, the particle has no potential energy relative to its own frame of reference because no work can be done on the particle without moving it away from that point.
  20. Jul 11, 2015 #19
    I am human and when I jump, I feel that I have potential energy, That potential came from the work I've done to go few centimeters high and the only frame I have is myself, tell me if I'm wrong !,
  21. Jul 11, 2015 #20
    Your first "No" answer of this question isnt it "Can we use the particle itself a referance frame to calculate this energy ?"

    Then my #10 post is correct I made right assumption.
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