fredreload Posted January 10, 2018 Share Posted January 10, 2018 As title suggested, is it possible? Link to comment Share on other sites More sharing options...
StringJunky Posted January 10, 2018 Share Posted January 10, 2018 Yes. Yarkovsky Effect. Quote The Yarkovsky effect is a force acting on a rotating body in space caused by the anisotropic emission of thermal photons, which carry momentum. It is usually considered in relation to meteoroids or small asteroids (about 10 cm to 10 km in diameter), as its influence is most significant for these bodies. Read more: https://en.wikipedia.org/wiki/Yarkovsky_effect 1 Link to comment Share on other sites More sharing options...
fredreload Posted January 10, 2018 Author Share Posted January 10, 2018 1 minute ago, StringJunky said: Yes. Yarkovsky Effect. Awesome Link to comment Share on other sites More sharing options...
StringJunky Posted January 10, 2018 Share Posted January 10, 2018 (edited) 17 minutes ago, fredreload said: Awesome Yes, it is interesting. I didn't know it as that, I had to look it up but I knew photon pressure was a real phenomenon. It's also the cause of the Pioneers anomaly that slowed them down as they left the solar system. Their net thermal emissions were in the direction of travel. Edited January 10, 2018 by StringJunky Link to comment Share on other sites More sharing options...
swansont Posted January 10, 2018 Share Posted January 10, 2018 People who take care of GPS satellites have to take this into account, since it will tend to push them off of their orbits. Any positioning error in the satellite correlates to positioning error on the earth. And radiation pressure is how solar sails work, as well as laser cooling of atoms and molecules. Link to comment Share on other sites More sharing options...
Strange Posted January 10, 2018 Share Posted January 10, 2018 51 minutes ago, swansont said: And radiation pressure is how solar sails work, as well as laser cooling of atoms and molecules. Maybe worth noting that it is not how a Crooke's Radiometer works, despite the fact that they are often described that way. (And, having just checked, another common explanation [that there is pressure from gas warmed by the dark side] is also incorrect!) Link to comment Share on other sites More sharing options...
StringJunky Posted January 10, 2018 Share Posted January 10, 2018 1 minute ago, Strange said: Maybe worth noting that it is not how a Crooke's Radiometer works, despite the fact that they are often described that way. (And, having just checked, another common explanation [that there is pressure from gas warmed by the dark side] is also incorrect!) I think that fails to work if there is a complete vacuum inside. Link to comment Share on other sites More sharing options...
DrP Posted January 10, 2018 Share Posted January 10, 2018 5 minutes ago, Strange said: Maybe worth noting that it is not how a Crooke's Radiometer works, despite the fact that they are often described that way. (And, having just checked, another common explanation [that there is pressure from gas warmed by the dark side] is also incorrect!) It's still a better explanation than 'Look! I am moving the vanes with the power of my mind!!" I have heard so many explanations for it that I am confused now. I think the vacuum is important to determine the direction of travel - Physics link suggests so anyway. It says that the light effects only work in a vacuum.... in a poor vacuum they are over ridden by a more dominant thermal effect which cause the opposite to happen of what you'd expect to happen in the vacuum. What the exact mechanism is I do not know - I thought it was transference of momentum from the photons absorbed into the black being different to the ones being reflected by the white... causing a net difference in momentum gain by each side of the vain which causes rotation. Now I am even more confused.... one thing I am confident about is that it isn't mind power doing it. lol. Actually I used to think it was just a thermal effect - but have been sold on the momentum gain from photons idea. Link to comment Share on other sites More sharing options...
swansont Posted January 10, 2018 Share Posted January 10, 2018 4 minutes ago, DrP said: It's still a better explanation than 'Look! I am moving the vanes with the power of my mind!!" I have heard so many explanations for it that I am confused now. I think the vacuum is important to determine the direction of travel - Physics link suggests so anyway. It says that the light effects only work in a vacuum.... in a poor vacuum they are over ridden by a more dominant thermal effect which cause the opposite to happen of what you'd expect to happen in the vacuum. What the exact mechanism is I do not know - I thought it was transference of momentum from the photons absorbed into the black being different to the ones being reflected by the white... causing a net difference in momentum gain by each side of the vain which causes rotation. Now I am even more confused.... one thing I am confident about is that it isn't mind power doing it. lol. Actually I used to think it was just a thermal effect - but have been sold on the momentum gain from photons idea. A Crookes radiometer spins the wrong way for it to be photon pressure. Absorption gives a momentum "kick" of p, but reflection gives a "kick" of 2p. The radiometer should spin in the direction of the black vanes, since the white vanes get pushed harder. But it spins the other way. You could also estimate the force on the vanes and probably see that the radiation pressure is too small to account for the spinning. 1 Link to comment Share on other sites More sharing options...
Strange Posted January 10, 2018 Share Posted January 10, 2018 9 minutes ago, DrP said: It's still a better explanation than 'Look! I am moving the vanes with the power of my mind!!" I have heard so many explanations for it that I am confused now. I think the vacuum is important to determine the direction of travel - Physics link suggests so anyway. It says that the light effects only work in a vacuum.... in a poor vacuum they are over ridden by a more dominant thermal effect which cause the opposite to happen of what you'd expect to happen in the vacuum. What the exact mechanism is I do not know - I thought it was transference of momentum from the photons absorbed into the black being different to the ones being reflected by the white... causing a net difference in momentum gain by each side of the vain which causes rotation. Now I am even more confused.... one thing I am confident about is that it isn't mind power doing it. lol. Actually I used to think it was just a thermal effect - but have been sold on the momentum gain from photons idea. Didn't really want to take this thread off topic (too late!) but if you want a good, detailed analysis of the explanations that do and don't work: http://math.ucr.edu/home/baez/physics/General/LightMill/light-mill.html 1 Link to comment Share on other sites More sharing options...
John Cuthber Posted January 10, 2018 Share Posted January 10, 2018 1 hour ago, Strange said: ...[that there is pressure from gas warmed by the dark side] is also incorrect!) Is it just me? 1 Link to comment Share on other sites More sharing options...
Strange Posted January 10, 2018 Share Posted January 10, 2018 (edited) 6 minutes ago, John Cuthber said: Is it just me? No! Even as I typed it ... Edited January 10, 2018 by Strange Link to comment Share on other sites More sharing options...
DrP Posted January 10, 2018 Share Posted January 10, 2018 2 hours ago, Strange said: Didn't really want to take this thread off topic (too late!) but if you want a good, detailed analysis of the explanations that do and don't work: http://math.ucr.edu/home/baez/physics/General/LightMill/light-mill.html 2 hours ago, swansont said: A Crookes radiometer spins the wrong way for it to be photon pressure. Absorption gives a momentum "kick" of p, but reflection gives a "kick" of 2p. The radiometer should spin in the direction of the black vanes, since the white vanes get pushed harder. But it spins the other way. You could also estimate the force on the vanes and probably see that the radiation pressure is too small to account for the spinning. ah good - photon momentum - that's what I thought. Thanks. Link to comment Share on other sites More sharing options...
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