[Video] What Travels Faster Than Light

By Anupum Pant

Like always, another one of those awesome Vsauce videos where Michael explains how darkness and scissor intersections can travel faster than light and still not go against any physics laws. So much to learn! Let me just say nothing today.

P.S there’s a mention of the Dunning Kruger effect and the story of Mr. Mc Arthur Wheeler I covered some time back on the blog.

Seeing Sound

You can skip everything under this subheading

Note: In the past, I’ve been requested by my readers to keep the articles on AweSci short. It made sense. Since I write one article everyday, for readers, it definitely is easier to read and digest a smaller article, day in and day out. Thanks to the rate at which short attention span is being nurtured by the internet, not all have the appetite to take in bigger pieces everyday.

I see it this way – doing a very little thing everyday religiously, compounds. It makes a huge difference in your life. Even devoting 2 minutes a day for a single thing makes big changes over time. Here, I’m doing more than an hour everyday! If you read these daily, you are devoting around 10 minutes a day to learn something. You’ll do great in life!

At the same time, smaller articles of about 300-500 words are good for me too. By sticking to smaller ones, I can accomplish my own goal of learning and writing about one new thing everyday, by doing less. Also, composing smaller articles doesn’t take a lot of time which allows me to take care of the primary daily activities.

However, today, a reader asked me about the decreasing length of my articles. It’s so good to know that readers actually care about these things. Nevertheless, as explained above, there’s nothing wrong in it, but it did make me think about what was causing it? Well, I’ve been busy with so much stuff for the past few days, I don’t have partners for the blog and it’s tough doing it alone. Still, with all the travelling and full day outings in a 40 degree sun for the past few days, I managed at least one article a day. Pat on the back to me for being able to do that.

Anyway, the point is that articles don’t have to be long. For the question my faithful reader asked me, I needed to write this to explain it to him. He deserves a good explanation for being faithful reader to my little blog. If I learn something and sleep a little bit smarter than the last day, I’ve accomplished my goal for the day. That way, the purpose of you reading this is served. That way, the purpose of the blog is served.

What do you say, long or short? Or, you are always welcome if you want to contribute on this blog. We have hundreds of people who’d come by daily to read your article!

Background

In the past, we’ve seen how geniuses at MIT have figured out a way to capture the beam of light on video, and have replayed it moving in slow motion. In simple words, moving light was captured on camera. Something which the human eye had never seen before was shown moving with the help of technique. But, then there are other invisible things too. Like sound!

Watching sound

Watching the iTunes visualization go, isn’t equivalent to watching sound. Visualizations and waveforms are merely a digital depictions of sound.

While listening to sounds can be too easy, seeing it with your eyes isn’t natural. For that, there is camera trick that can be used to see the actual sound waves travelling in the air. In fact, with this technique, any disturbance in the air can be seen which otherwise, would be totally invisible to the naked eye. It let’s you see sound!

The camera technique has a fairly confusing name. It’s called Schlieren flow visualization. But that shouldn’t confuse you because in simple words, with this technique it is possible to capture on film, the disturbances that are caused by things moving in the air. For example, the invisible disturbances that are caused in the air (a transparent medium) when someone claps can be made visible by using the technique – Schlieren flow visualization.

Here is how it works

Photograph of a wind tunnel model using a schlieren system along  with a schematic explaining the operation of the system

If I write it in words, I’ll only confuse you more. So, here is an NPR video that explains the mechanism very accurately. Otherwise, there’s always this NASA page for it.

Amazingly, like the video shows, it can be used to see the heat coming off the human body. Now, I can definitely think of some creative applications for that.

Yes, Light Can Push Physical Objects

By Anupum Pant

Tim is a 71-year-old eccentric who has been collecting interesting toys for 50 years now. Today he has a collection of around 250,000 absurd toys in suitcases, labeled and stacked in a room from the floor to the ceiling. He shows them off in a Youtube channel regularly. I almost never miss any of his toys. Usually most the toys he displays amaze you, but do not blow off your mind. The last one did.

Before this, I had not known that light can push or move a physical object. So, I decided to investigate a bit.

The Extraordinary Toy

In his last video, he showed off a beautiful glass bulb mounted on a wooden stand, that he says has been made by some German company. The bulb has a very good vacuüm (not complete vacuüm, just enough to not create unnecessary drag for the vanes) and encloses a fan-like structure that starts rotating when a bright light is switched on near it. Some people call it the light mill – like the wind mill moves with the wind, this one moves when photons hit it. If give enough time, the mill can accelerate to really good speeds (at thousands of rounds per minute). Watch the video below. [Video]

Theories on how a radiometer really works

The device, a special kind of radiometer, was invented around 140 years back in the year 1873, by Victorian experimenter Sir William Crookes to measure the radiant energy of heat or light. It has four vanes mounted at the edge of four stiff wires to make a fan, each of which has a black side and a silvered side. All of this is enclosed in a bulb which is evacuated enough to not cause drag due to air. In complete vacuüm the vanes move in an opposite direction, but that experiment is really difficult to recreate!

  1. When light is turned on, the fan moves in a way that makes it look as if light is pushing away the black colored side. The theory of photons pushing the black side was accepted initially. But soon a problem was seen with the theory. If light is absorbed at the blackened side and reflected at the silvered side, the fan should be moving in the opposite direction.
  2. Then came in the other explanation which explained that the heated black side due to absorbed radiation rarefied the air near the black side and hence caused the gas to rush in and push that side. The greater the heat, the more this back side would get pushed and it would spin faster. Later even this theory was proved to be wrong. But, Britannica, till date decides to go with this explanation – to some extent this theory goes in the right direction, you will see why…
  3. One more theory claimed that the heat evaporated the impurities on the black side, whose force made it spin.

How the radiometer really works?

The correct explanation was given by a  prominent Anglo-Irish innovator, Osbourne Reynolds. He explained it by mentioning a porous plate, where the air inside the holes would flow from the colder sides to the warmer side (obviously) and make the vanes spin in the opposite direction. He called it “Thermal Transpiration” – makes sense and is easy to understand. But the vanes here are not porous. So…

He said that “Thermal Transpiration” in the vanes takes place at the edge of the vanes and not the faces. Think of edges as small pores, he said.

Due to a temperature gradient formed, the air starts moving along the surface from colder to the warmer side through the edges. The net pressure difference around the vane is created which pushes it in a direction that is away from warmer air and towards the colder air – makes sense for the apparatus.

This is the reason, if it is cooled, it moves in the opposite direction.

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