Tag: heat

Seeing Sound

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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.

Mpemba Effect – Hot Water Freezes Faster Than Cold Water

By Anupum Pant

In the past, we have seen that when it comes to estimating temperature, we are not so smart. Once again seeing the Mpemba Effect defying all known logic, reminds me to be careful about applying logic to most of the natural phenomena which are seemingly simple but in reality are extremely complicated.

By applying simple logic, a 7-year-old could tell you that cold water should turn into ice quicker than hot water would. It should, because a hot liquid contains a lot more heat as compared to a colder liquid, which [the heat]  has to be removed in order to freeze it. Yes, it is what anyone who is unaware of the Mpemba Effect would think. But, that isn’t the case with water. It turns out that a very common substance – water – is not as simple as it looks.

Mpemba Effect

Since the time of Aristotle and Descartes, scientists have noted that hot water can freeze faster than cold water (and yet the effect is not popularly known among us today). Although the effect was noted back then, the actual mechanism which caused it remained a mystery all along…until the year 2013.

All this time this effect must have been known by some other term because, it was not until the 1960s it was named “Mpemba effect”. It was named that after a Tanzanian cookery student Erasto Mpemba when he observed that hot ice cream mix froze faster than the cold mix.

Several theories have tried to explain the mechanisms that cause the Mpemba Effect. Not even one of them was convincing enough. Probably this is what propelled the geniuses from Singapore who could finally solve this mystery during the month of October this year.

What causes it?

In simple words, Hydrogen bonds cause this effect – faster freezing hot water. Normally, individual water molecules are connected by this bond called the Hydrogen bond. Think of the water molecule as a string with two bullies – hydrogen bonds – one on either side. These Hydrogen bonds pull this string from both sides. As a result, the string stretches. We’ve all fought with rubber bands and know that a stretched string has a butt load of energy stored inside it. The same thing happens with water. Energy is stored in stretched water molecules at normal temperature. This extra energy has to be removed to cool water.

At a higher temperature, the heat kind of weakens these bullies. So, the weak bullies aren’t able to pull the string as much. Now, individual molecules sit apart. They are no longer stretched. Thus, not much energy is stored in these strings anymore. They have given up energy. There is no longer any extra energy that needs to be removed. Hence, cooling is faster.

Sorry: Today I don’t have my buddy – the internet – with me. So, you won’t see any outgoing reference links today. I have a just a bit of internet (a slower 2G connection) which I’m using up to publish this.

A Flashlight That Uses Body Heat Instead of Batteries

By Anupum Pant

I talked about a light that utilizes the power of gravity to light up a few days back. This flashlight is a bit similar in a way that, it also doesn’t need any batteries. But the underlying mechanism it uses, is completely different.

The winner of this year’s Google Science Fair, in the age group of 15-16, was a 15-year-old girl from Canada, Ann Makosinski. In her project she created a flashlight that, instead of batteries, uses our body heat to light up. She calls it “Hollow Flashlight”

The flashlight uses 4 Peltier tiles to convert the temperature difference (between body and room temperatures) into energy. One side of the tiles is heated by our body heat and the other side is at room temperature. This temperature difference creates electricity using the Thermoelectric effect. The tiles used for this light need a minimum of 5 degree difference of temperature to work.

Peltier Tiles

Peltier tiles utilize thermoelectric effect to convert temperature difference into electricity. When there is a enough temperature difference, charge carriers move from hot area to the colder area. This separation of charges builds up a potential difference across the height of the tile. This potential difference can be used up for various things. In this case, it was used to light up LEDs.

Advantages: The amount of potential difference produced depends on the material. Peltier tiles are great because they are compact and they do not use any moving parts. Elimination of any moving parts eliminates wear and tear. They last long and do not need a lot of maintainance. However, their efficiency is not so great. So, they are used only where long life is essential.
The Voyager space probe and other deep space probes, where long life is of prime importance, use Thermoelectric generators (another image). The heat there is produced by a radioactive isotope. Implanted pacemakers which require long life also use it as a source of energy. All of them work utilizing the same effect – thermoelectric effect. The eco-fan, a wood stove fan, also uses the same effect in a very creative way.

Thermoelectric Generators have a very interesting history.

Why is a Metal Plate “Colder” Than a Plastic Plate?

by Anupum Pant

No, it isn’t!

What is Cold?

According to the dictionary, a body at a relatively lower temperature, especially when it is compared to the temperature of a human body is described as a colder one. So, any object below the normal human body temperature – about 37 degrees Celsius – is a cold thing. But wait a minute!

When you touch an object, what does it tell you about the temperature of the object? Can you really judge if it is a cold one or a hot one? Unfortunately, our bodies aren’t thermometers, we are not so smart when it comes to judging the temperature. Consider the following case.

A book and a steel plate kept in the same environment for a long time attain the same temperature eventually (it is called thermal equilibrium). This can be checked by using a thermometer on both the objects. But, when people are asked to touch a metal plate and a book, they find the former to be much cooler. You can try this out yourself by touching different materials around you. You’ll see how some things ‘feel colder’ while the others feel warmer. A YouTube channel Vertasium conducted a social experiment to record this on camera. See the video below:

There is no cold – only heat

So, in the video, ice melts faster, if kept on steel plate than on a plastic plate, even when the steel plate ‘feels colder’. Common sense dictates that the colder thing is supposed to sustain the ice block for a longer time, just like your refrigerator does. So why does the opposite happen?

A better way to understand this ‘contradiction’ (not really a contradiction) can be this:

According to thermodynamics, simply put, everything has heat in it. So, even a cold ice block has some amount of heat stored in it (say, around 273.15 Kelvin or 0 degree Celsius). When one object comes in contact with other object, it loses or gains heat till their temperatures get equal or till they attain ‘thermal equilibrium’. Which object loses heat and which one gains it, is decided by their relative temperatures. In case of ice and steel, ice has a lower temperature than steel (assuming it isn’t already freezing out there). Therefore, here, ice gains heat from steel till they attain the same temperature and ice melts.

Side note: The ice is also in contact with a relatively ‘hotter’ atmosphere. Hence, it gains heat from there also. In this case, we are only concerned about the steel and ice interaction.

Why does it melt faster on steel?

There is a particular property which depends on the kind of material and is called thermal conductivity. This is the parameter which decides which objects lose heat quicker and which ones do it slower.

Here, for instance, steel has a higher thermal conductivity than plastic. Hence, the steel plate gives away heat to the ice block faster than a plastic block does. As a result, ice melts faster on a steel plate than on a plastic one.

Incidentally, this effect can also be used to explain why one plate feels colder than the other, in our hands. Think of it like this, the ice is replaced by our hand. So, a steel plate, due to its better thermal conductivity, draws heat faster from our hand than a plastic plate. This makes us feel that the steel plate is colder than the plastic one.

As checked by a thermometer, both the plates have the same temperature, our bodies are only fooled into believing that the thing we feel is temperature; it isn’t. None of the plates is actually colder than the other (according to the dictionary – see first paragraph). We don’t feel the temperature. What we feel is actually the rate of heat being drawn away from our hand. Faster an object draws heat, the colder it feels.