[ARCHIVED THREAD] - how much does light weigh? (Page 1 of 3)
Posted: 12/29/2009 2:32:58 PM EDT
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ok, so a photon of light travels 299,792,458 meters per second. so if they can measure how fast a photon travels... so it has mass, right? so how much does a photon weigh? how about a cubic meter or light? cubic kilometer? this is the kind of stuff that keeps me up at night. |
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Huh... funny. I always figured that the photon was the object with the least mass possible, thus its ability to obtain (and set) relativistic speeds. That our understanding of it having no mass is more a function of our inability to thus far calculate said mass, rather than it having none. |
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The mass of a photon is relativistic. It has no mass when not moving because it is pure energy, according to Einstein's famous e=mC^2 Get a radiometer and then draw the free body diagram of the torque, noting the reflective and absorptive vanes, using conservation of momentum. |
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Quoted: Huh... funny. I always figured that the photon was the object with the least mass possible, thus its ability to obtain (and set) relativistic speeds. That our understanding of it having no mass is more a function of our inability to thus far calculate said mass, rather than it having none. got it. thanks. |
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Huh... funny. I always figured that the photon was the object with the least mass possible, thus its ability to obtain (and set) relativistic speeds. That our understanding of it having no mass is more a function of our inability to thus far calculate said mass, rather than it having none. "inability to thus far calculate said mass"... Yup, photons have/are energy, so they must have mass. 
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How do those things work, with the diamond shaped paddles, black on one side, white on the other that start spinning when you put them in sunlight? What 'pushes' the paddles? The expansion of air as it is heated by the black side (which absorbs more radiant energy). |
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How do those things work, with the diamond shaped paddles, black on one side, white on the other that start spinning when you put them in sunlight? What 'pushes' the paddles? The expansion of air as it is heated by the black side (which absorbs more radiant energy). No, light exerts pressure on an object. across a 1sq mile flat, reflective surface it exerts the same pressure as if a marble was sitting on that same surface at sea level on the Earth. Solar sails, BTW, are the reason I know this. |
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How do those things work, with the diamond shaped paddles, black on one side, white on the other that start spinning when you put them in sunlight? What 'pushes' the paddles? The expansion of air as it is heated by the black side (which absorbs more radiant energy). No, light exerts pressure on an object. across a 1sq mile flat, reflective surface it exerts the same pressure as if a marble was sitting on that same surface at sea level on the Earth. Solar sails, BTW, are the reason I know this. Then why is more pressure exerted on one side of the paddle than the other? |
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How do those things work, with the diamond shaped paddles, black on one side, white on the other that start spinning when you put them in sunlight? What 'pushes' the paddles? The expansion of air as it is heated by the black side (which absorbs more radiant energy). No, light exerts pressure on an object. across a 1sq mile flat, reflective surface it exerts the same pressure as if a marble was sitting on that same surface at sea level on the Earth. Solar sails, BTW, are the reason I know this. Then why is more pressure exerted on one side of the paddle than the other? Because the white side of the paddle is obviously racist, duh. 
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so if photons are going away from you at the speed of light, aren't you going away from the photons at the speed of light from their perspective? If so, how come I can go the speed of light and not have to use infinite energy? If someone drives a car at 70 mph away from you, are you travelling 70 mph away from them? Or are you standing still? |