# Question About Mass

Discussion in 'Physics & Math' started by OilIsMastery, Nov 30, 2008.

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1. ### OilIsMasteryBannedBanned

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

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3. ### BenTheManDr. of Physics, Prof. of LoveValued Senior Member

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Yes.

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5. ### OilIsMasteryBannedBanned

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Can you say more please? How? Can you give an example? Scientific reference? Link?

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7. ### BenTheManDr. of Physics, Prof. of LoveValued Senior Member

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Before you ask: conservation of momentum.

8. ### BenTheManDr. of Physics, Prof. of LoveValued Senior Member

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Before you ask: yes, photons have momentum.

9. ### OilIsMasteryBannedBanned

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How is that possible?

p=mv right?

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

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11. ### BenTheManDr. of Physics, Prof. of LoveValued Senior Member

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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.

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13. ### OilIsMasteryBannedBanned

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So physicists rewrote the momentum equation for the photon?

Last edited: Nov 30, 2008
14. ### BenTheManDr. of Physics, Prof. of LoveValued Senior Member

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There is no conservation of mass.

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17. ### OilIsMasteryBannedBanned

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Why did physicists rewrite the momentum equation for photons?

Last edited: Nov 30, 2008
18. ### BenTheManDr. of Physics, Prof. of LoveValued Senior Member

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State the law of conservation of momentum, please.

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p=mv?

20. ### BenTheManDr. of Physics, Prof. of LoveValued Senior Member

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how does one see conservation of momentum from this statement?

21. ### OilIsMasteryBannedBanned

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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?

22. ### TrippyALEA IACTA ESTStaff Member

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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.

23. ### OilIsMasteryBannedBanned

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Great, that doesn't answer my questions so thanks for nothing.