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How can a photon have kinetic energy if it has zero rest mass?
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Because it has a non-zero apparent mass due to traveling at the speed of light.
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I didn't think photons had kinnetic energy. The have momentum and energy. But kinetic energy sounds like a misnomer to me.
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I didn't think photons had kinnetic energy. The have momentum and energy. But kinetic energy sounds like a misnomer to me.
You are probably right about this. Electromagnetic waves certainly have energy and momentum, but does that mean thier energy is kinetic?
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It is written in physics books that photons have kinetic energy.
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I belong to the Kinesiology Department at my university. It used to be called the Physical Education Department--could it be you're just having an argument about terminology?
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Electromagnetic waves have electromagnetic energy. EM energy can be absorbed and turned into kinetic energy. They do so by exerting a force on the object they hit (usually a magnetic force on spinning electrons in an atom's orbit). Since by applying a force they are imparting a momentum onto the object they hit, one could say by analogy that the EM wave had momentum that it transfered to the object. But we're talking about electromagnetic momentum, not p=mv.
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If the photon carries momentum, and kinetic energy it must therefore have mass even at rest! This is a new law of physics!
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But we're talking about electromagnetic momentum, not p=mv.
Please errorlist, at least read the posts of people who are trying to help you.
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Actually, I think that p=mv applies when m is the "relativistic mass" of the photon. However, the photon still has 0 rest mass, if it did not the relativistic mass would be infinite.
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Mark Friedenbach ,
Yes, I have read the replies, and have made my own conclusions. It just does not make sense. Momentum, and kenetic energy in a particle that have zero rest mass does not exist.However, the mass of that particle is still there.Zero rest mass implies there is a particle.If you start out with nothing (zero speed, and zero mass) you don't gain mass from zero just because there is movement. ZERO=ZERO even if zero is moving at the speed of light.
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Simply because it doesn't make sense to you doesn't mean it isn't right Errorist... in fact I would be tempted to use it as a litmus test for clarity and accuracy...
You are still thinking in terms of Newtonian physics with a little Einstein sprinkled in on top. To make a long story short, you aren't coming from the correct physics background... Newton was wrong.
It IS possible for particles to have no mass, and it is possible for them to behave as if they had mass if they are moving. If you want to know why, then you are on the precipice of Quantum Mechanics realm, where matter/mass/etc aren't applicable concepts.
[i]"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw[/i]
[i]The glass is at 50% of capacity[/i]
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