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Name: Glenn
Status: student
Grade: 9-12
Country: United Kingdom
Date: N/A 


Question:
Why does wind not bend light? I was watching a film this evening. A couple of fellows where walking through a sandstorm. They carried torches and the beams of light the torches produced where straight. Why are the photons not affected by wind? Photons are affected by their environment ... a prism is evidence of that. Is it not?



Replies:
Hi Glenn,

Light *is* bent by wind, but at short distances, it does not bend enough for us to see (with unaided eyes). As light moves between materials of different density, the light beam bends (the prism has much higher density than air, so you can see it bend). Unlike glass, the density differences in the air caused by wind are much, much lower, so the bending caused by wind is just not enough to see with the unaided eye at short distances.

A longer-distance example you may have heard of is a mirage. A mirage is created by density differences in air caused by temperature, not wind, but a mirage is definitely visible to the human eye. The mirage example involves a longer distances than your example with torches (flashlights) -- once you get close to where the mirage appeared to be, you find it's no longer there (because as you get closer, the light bends less, causing the mirage image to no longer be visible).

Hope this helps,
Burr Zimmerman


There may be more complicated explanations, but a short explanation is that the speed of the photon is so much greater than the speed of a wind, that the two are essentially uncoupled. Now if the light and wind are "coupled" because the speed of the flame is about that of the wind, there will be a distortion of the flame, but this is an interaction of the flame and the wind. The photons just track the path of the wind that drives the flame.

Vince Calder


Glenn

Air density, which is effected by wind, effects light paths. The effect is known as scintillation. Common examples are the mirage of water on the surface of asphalt on hot days and twinkling stars. That is the bending of light waves such that the distant highway is obscured by the color of the sky.

Go to http://www.www.google.com and search for "Scintillation" to find a whole host of articles on the phenomenon.

Sincere regards,
Mike Stewart


Glenn,

A prism bends light because it delays light. The glass atoms absorb individual photons for a very short time, and then they release them back to the environment. This is a property of dense transparent materials, usually liquid or solid. A sandstorm is mostly air, which has little effect. Sand can absorb photons, but it will not release them so quickly. Most of the absorbed photons will heat up the sand. Some will be reflected back just like the wall reflects light. Grains of sand are not transparent.

Ken Mellendorf



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