4 ms·

Crazy Material That You Can Make at Home That Bends Light

peter_d_sherman 6y ago
The "material" is a fluid made by mixing sugar and water, and letting it sit for a few days. The net effect is that a density gradient in the fluid occurs, that is, there's a higher water-to-sugar ratio on the top, and a higher sugar-to-water ratio on the bottom. The near bottom of such a pool will bend the (otherwise perfectly straight) beam of light emitted by a laser pointer... A highly interesting effect, to be sure...
- gus_massa 6y ago
  It's a nice experiment, but but the impatient poephttp://www.youtube.com/watch?v=968gVUAY9Mg&t=7m40s http://www.youtube.com/watch?v=968gVUAY9Mg&t=7m40s The first part is a discussion about refractive index, the details of the experiment are discussed in the second part. Some detail of the explanation are slightly wrong. If you start with a setup like in this experiment with water over a layer of sugar, after some time you will get the gradient to make the experiment. But if you wait too much the diffusion will mix everything evenly, and the light will not blend. It's not caused by the difference of density, but the difference of density will help to maintain the gradient for some time anyway.
  - peter_d_sherman 6y ago
    >"Some detail of the explanation are slightly wrong. If you start with a setup like in this experiment with water over a layer of sugar, after some time you will get the gradient to make the experiment. But if you wait too much the diffusion will mix everything evenly, and the light will not blend. It's not caused by the difference of density, but the difference of density will help to maintain the gradient for some time anyway." Agreed completely -- there is an effect not related to density going on. But, I at this point in time -- can't wrap my mind around it, nor speculate as to exactly what that effect might be and how it might work and why it might work... It needs (at least to me, in the future) -- more study. That's why I post a lot of the videos I do; I don't have a lab; I don't have any esoteric equipment or materials to experiment with (in the above case, while I have the sugar and water(!) (who doesn't? <g>), I lack the prerequisite laser pointer, how lame is that? <g> (I chose intentional poverty so I can have TIME to work on the things I want to work on, mostly related to writing and programming at this point in time...)), and so I post a majority of the videos I post on HN as "Future To-Do List Items", that is, "These would be interesting areas to revisit -- when more resources are present..." But, agreed -- The effect is not caused by the difference of density...
    - gus_massa 6y ago
      There are three interesting properties: * Sugar concentration * Density * Refractive index They are related, but it's not an easy linear relation. It's important that the sugar initially is at the bottom and the water with a high concentration of sugar has higher density. So the water does not move too much, and the sugar moves slowly by diffusion. If you try the same experiment hanging a sugar cube or a candy at the top, the water with a high concentration of sugar will go down and make produce something like convection. (Is the official name for this convection too?) Someone made and posted an experiment with hot and cold water. The colorant is not important, but makes everything easier to see. https://news.ycombinator.com/item?id=23375765 https://news.ycombinator.com/item?id=23375765 -- You can try to reproduce the experiment in the current video without a laser. A strong flashlight with some cover with a small hole should be enough. (A laser is better because it's usually stronger.) You can try adding a drop of milk to make the light easier to see. It's nice a transparent liquid, but a few drops of milk may make everything easier. Remember to stir the water after you put the milk, and wait until all the movement disappears. And no NOT stir after you put the sugar. Don't move the glass. Keep it as quiet as possible. Another trick that may help is to change the background (a darker background is usually better) and reduce the global illumination. I'm not sure if he explain the amount of sugar you should put, but you may need to try a few times to get the correct amount of sugar and the time to wait. If you ever do the experiment, remember to post a few photos here.

The "material" is a fluid made by mixing sugar and water, and letting it sit for a few days. The net effect is that a density gradient in the fluid occurs, that is, there's a higher water-to-sugar ratio on the top, and a higher sugar-to-water ratio on the bottom. The near bottom of such a pool will bend the (otherwise perfectly straight) beam of light emitted by a laser pointer... A highly interesting effect, to be sure...

gus_massa 6y ago
It's a nice experiment, but but the impatient poephttp://www.youtube.com/watch?v=968gVUAY9Mg&t=7m40s http://www.youtube.com/watch?v=968gVUAY9Mg&t=7m40s The first part is a discussion about refractive index, the details of the experiment are discussed in the second part. Some detail of the explanation are slightly wrong. If you start with a setup like in this experiment with water over a layer of sugar, after some time you will get the gradient to make the experiment. But if you wait too much the diffusion will mix everything evenly, and the light will not blend. It's not caused by the difference of density, but the difference of density will help to maintain the gradient for some time anyway.
- peter_d_sherman 6y ago
  >"Some detail of the explanation are slightly wrong. If you start with a setup like in this experiment with water over a layer of sugar, after some time you will get the gradient to make the experiment. But if you wait too much the diffusion will mix everything evenly, and the light will not blend. It's not caused by the difference of density, but the difference of density will help to maintain the gradient for some time anyway." Agreed completely -- there is an effect not related to density going on. But, I at this point in time -- can't wrap my mind around it, nor speculate as to exactly what that effect might be and how it might work and why it might work... It needs (at least to me, in the future) -- more study. That's why I post a lot of the videos I do; I don't have a lab; I don't have any esoteric equipment or materials to experiment with (in the above case, while I have the sugar and water(!) (who doesn't? <g>), I lack the prerequisite laser pointer, how lame is that? <g> (I chose intentional poverty so I can have TIME to work on the things I want to work on, mostly related to writing and programming at this point in time...)), and so I post a majority of the videos I post on HN as "Future To-Do List Items", that is, "These would be interesting areas to revisit -- when more resources are present..." But, agreed -- The effect is not caused by the difference of density...
  - gus_massa 6y ago
    There are three interesting properties: * Sugar concentration * Density * Refractive index They are related, but it's not an easy linear relation. It's important that the sugar initially is at the bottom and the water with a high concentration of sugar has higher density. So the water does not move too much, and the sugar moves slowly by diffusion. If you try the same experiment hanging a sugar cube or a candy at the top, the water with a high concentration of sugar will go down and make produce something like convection. (Is the official name for this convection too?) Someone made and posted an experiment with hot and cold water. The colorant is not important, but makes everything easier to see. https://news.ycombinator.com/item?id=23375765 https://news.ycombinator.com/item?id=23375765 -- You can try to reproduce the experiment in the current video without a laser. A strong flashlight with some cover with a small hole should be enough. (A laser is better because it's usually stronger.) You can try adding a drop of milk to make the light easier to see. It's nice a transparent liquid, but a few drops of milk may make everything easier. Remember to stir the water after you put the milk, and wait until all the movement disappears. And no NOT stir after you put the sugar. Don't move the glass. Keep it as quiet as possible. Another trick that may help is to change the background (a darker background is usually better) and reduce the global illumination. I'm not sure if he explain the amount of sugar you should put, but you may need to try a few times to get the correct amount of sugar and the time to wait. If you ever do the experiment, remember to post a few photos here.