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Need Ratiocination

  1. Oct 23, 2003 #1
    Hi Guyz, As we know the gravitation constant newton discovered is 6.67*10^-11 Unit : (Newoton * Meter Square / KiloGram Square) and we use it in the formula

    F = K m1 m2 r^-2

    F : Gravitation Force We Get.
    K : Newtons Constant.
    m1: First Body Mass.
    m2: Second Body Mass.
    r : Distance Between The Two Bodies.

    And Coloumbs Constant for Electrical Charges Is 9*10^9 Unit : (Newton Meter Square / Coloumb Square) Which Equals 1/(4πε), ε = 8.85*10^-12 And we use it in the formula :

    F = K q1 q2 r^-2

    F : Gravitation Or Inconsistency We Get.
    K : Coloumbs Constant.
    q1: First Charge.
    q2: Second One.
    r : Distance Between.

    I want to know how did newton and coloumb get these constant.

    I don't think it's an easy question :P lol !!

    See ya guyz, Mail me if it's a file, destroyer@samer.ws
  2. jcsd
  3. Oct 23, 2003 #2


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    The value of the constants is simply a result of our choice of fundamental units, like the meter, kilogram, etc. You can adopt a different set of fundamental units in which G is 1, for example. Many working physicists do this to simplify their calculations.

    - Warren
  4. Oct 23, 2003 #3


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    Essentially you get G by measurement. You measure how much force exists between two known masses and calculate G from it.

    Newton estimated it by guessing the Earth's mass and then calculating it from the measured value of acceleration from gravity.

    The first actual measurement was doen by Henry Cavendish.
  5. Oct 23, 2003 #4

    No Guyz, This can't be, Those constants are not random, or by measuring, for example, when blank found his constant for the electro-photonic cells, he used the formula :

    qe Vs = 1/2 m V^2 = h(f-f0)

    Vs = hf/qe - hf0/qe

    While ..

    Vs : Cutting Voltage.
    qe : The Charge Of The Electron ( It equals 1.6 * 10^-19)
    f : Frequency of the photonic light. f0 Is the Minimum Frequency Required to Release the Electron From the AlKali Without giving him any Kenitec Energy.
    h : Blanks Constant, After Drawing The Line Of that equation, We will calculate the derivative of the tangent which will equal 6.6256*10^-34

    Constants are being calculated this way,

    I want to know what are the equations they used, And how,

    Any one professional to answer?
  6. Oct 23, 2003 #5


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    No one said that constants are "random". One person did note that constants of nature depend upon the units you use: obviously if you measured force in pounds and distance in feet, you would get quite a different value for G than when force is in Newtons and distance in meters. It is possible to choose your units so that G is 1.

    Once a specific choice of units is made, the direct way to determine such constants IS through experimentation and measurement.
    If one used a formula as you suggest, that would be an indirect way based on other constants that were calculated by measurement.

    Janus and chroot were completely correct.
  7. Oct 24, 2003 #6


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    Not random, just arbitrary. And they must be found by a combination of measurement and calculation (thats the only way we can find mathematical relationships). But don't fall into the trap of thinking that something that is somewhat arbitrary has a diminished significance. Whether the speed of light is 300,000 km/sec or 186,000 miles/sec or just plain "C," (1C) the speed of light is the same.
  8. Oct 24, 2003 #7
    I don't think so ...

    It's impossible to measure such a thing, especially because the number he gave is very small !! (6.67*10^-11) ... There must be some equations, something they made, i'm studying pure physics 4 years ago, and now i'm in the faculty of physics, all scientists ways i saw was the same, my school or university didn't gave them to us maybe because they are maybe complicated or somthing, Nothing in physics can be done without equations, that's what i learned 4 years ago, so ... i'm sure those things can be found on the internet, but i'm not able to make any search, because i studied physics symbols in the English language, but explanation wasn't english, that's why i'm not able to make any seach ...

    Any one can find them for me?
  9. Oct 24, 2003 #8


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    Re: I don't think so ...

    The equation for finding G is

    G = Fd2/Mm

    If you have two masses M and m, separate them center to center by a distance of d, and then measure the force between them you can calculate G.

    Cavendish did this by putting masses on the end of a long rod, suspending this rod at its center by a piano wire, placing two more large masses near the first two in such a way that the gravity betwen them put a torque on the piano wire which he was able to measure to get F.

    This is the only way you can come up with a value for G. (Newton got his by making an astute guess at the Earth's mass, and then using the experimentally measured value for g(9.8m/sec/sec) to determine F)
  10. Oct 24, 2003 #9


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    Re: I don't think so ...

    Uh, no. It's not impossible.
    That's terrifying. Please don't come near my children (when I have them).

    - Warren
  11. Oct 24, 2003 #10
    MAN !! Can you do this thing your self? can you put 2 cars for example beside each other and then measure up the force between them?

    Guyz, my question is what's the way they used exactly, not an example for the way !!!

    And also i need the constant of coloumb ....

    I'm sorry for repeating the question, but no body is giving me the answer ....
  12. Oct 24, 2003 #11


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    I am amazed that you have studied 4 years of physics and do not already know the answer to these questions. Re read the post by Janus. He described exactly the experiment done by Cavendish to directly measure G.
    Do a web search on Cavendish, you should get lots of hits.

    since you posted Coulombs constant I would guess that you want the method. Simply replace the massive balls of Cavedish with charged spheres, measure the force between them at various distances.

    Google is your friend.
  13. Oct 24, 2003 #12

    Chi Meson

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    A later experiment by a guy named Von Joli (can't remember the first name) got a more accurate value for G. His method used a balance beam that had a very long arm on one side and a short one on the other. He had it balanced precisely, then rolled a huge lead sphere under the pan on the long arm side, and it dipped slightly. He rebalanced the beam, and determined the additional force due to the lead sphere.
  14. Oct 25, 2003 #13

    Our physics books writers wanted us to know physics as they want, That's why they wrote the things they see important than others,
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