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Thread: Question About Mass

  1. #1

    Question About Mass

    Q: Is it possible for something with no mass to move something that has mass?

  2. #2
    Dr. of Physics, Prof. of Love BenTheMan's Avatar
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    Yes.

  3. #3
    Quote Originally Posted by BenTheMan View Post
    Yes.
    Can you say more please? How? Can you give an example? Scientific reference? Link?

  4. #4
    Dr. of Physics, Prof. of Love BenTheMan's Avatar
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    Before you ask: conservation of momentum.

  5. #5
    Dr. of Physics, Prof. of Love BenTheMan's Avatar
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    Before you ask: yes, photons have momentum.

  6. #6
    Quote Originally Posted by BenTheMan View Post
    Before you ask: yes, photons have momentum.
    How is that possible?

    p=mv right?

    So momentum for a so-called "massless" photon would be p = 0 x c = 0.

  7. #7
    Dr. of Physics, Prof. of Love BenTheMan's Avatar
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    Before you ask: 1923 by Arthur Compton.

    http://www.aip.org/history/gap/Compton/01_Compton.html

  8. #8
    Dr. of Physics, Prof. of Love BenTheMan's Avatar
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    Quote Originally Posted by OilIsMastery View Post
    How is that possible?

    p=mv right?

    So momentum for a so-called "massless" photon would be p=0xc = 0.
    No. Learn physics.

    For a photon, p = h f / c, where h is plack's constant, f is the frequency of the wave, and c is the speed of light.

  9. #9
    Quote Originally Posted by BenTheMan View Post
    Before you ask: 1923 by Arthur Compton.

    http://www.aip.org/history/gap/Compton/01_Compton.html
    No mention of photons or massless particles.

  10. #10
    Quote Originally Posted by BenTheMan View Post
    No. Learn physics.

    For a photon, p = h f / c, where h is plack's constant, f is the frequency of the wave, and c is the speed of light.
    So physicists rewrote the momentum equation for the photon?
    Last edited by OilIsMastery; 11-30-08 at 02:31 PM.

  11. #11
    Dr. of Physics, Prof. of Love BenTheMan's Avatar
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    There is no conservation of mass.

  12. #12
    Quote Originally Posted by BenTheMan View Post
    There is no conservation of mass.
    http://en.wikipedia.org/wiki/Conservation_of_mass

  13. #13
    Dr. of Physics, Prof. of Love BenTheMan's Avatar
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    Do you read your own references?

    The law of "matter" conservation (in the sense of conservation of particles) may be considered as an approximate physical law that holds only in the classical sense before the advent of special relativity and quantum mechanics. Mass is also not generally conserved in open systems, when various forms of energy are allowed into, or out of, the system. However, the law of mass conservation for closed systems, as viewed from their center of momentum inertial frames, continues to hold in modern physics.

  14. #14
    Why did physicists rewrite the momentum equation for photons?
    Last edited by OilIsMastery; 11-30-08 at 02:31 PM.

  15. #15
    Dr. of Physics, Prof. of Love BenTheMan's Avatar
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    State the law of conservation of momentum, please.

  16. #16
    Quote Originally Posted by BenTheMan View Post
    State the law of conservation of momentum, please.
    p=mv?

  17. #17
    Dr. of Physics, Prof. of Love BenTheMan's Avatar
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    how does one see conservation of momentum from this statement?

  18. #18
    Quote Originally Posted by BenTheMan View Post
    how does one see conservation of momentum from this statement?
    I don't know. I'm supposed to be the ignorant one. I came here asking the questions. I didn't come here asking questions because I have answers.

    One of my questions is, why did physicists change and rewrite the momentum equation p=mv for photons?

  19. #19
    ALEA IACTA EST Trippy's Avatar
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    Quote Originally Posted by OilIsMastery View Post
    I don't know. I'm supposed to be the ignorant one. I came here asking the questions. I didn't come here asking questions because I have answers.

    One of my questions is, why did physicists change and rewrite the momentum equation p=mv for photons?
    Here's a clue (because this is painful, like watching a fish gasping and flopping in the bottom of a boat).

    p=mv doesn't state the conservation of momentum.
    It's the clasically derived equation for calculating the momentum of a massive body.
    It's a special case of a broader equation that is valid only in a small set of situations.

  20. #20
    Quote Originally Posted by Trippy View Post
    Here's a clue (because this is painful, like watching a fish gasping and flopping in the bottom of a boat).

    p=mv doesn't state the conservation of momentum.
    It's the clasically derived equation for calculating the momentum of a massive body.
    It's a special case of a broader equation that is valid only in a small set of situations.
    Great, that doesn't answer my questions so thanks for nothing.

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