Tag: cold

Screaming Coin and a Singing Spoon

By Anupum Pant

Dry ice, or Cardice – as British researchers call it, is a solid form of carbon dioxide. When carbon dioxide is cooled below temperatures of -78.5 degrees centigrade, the gas gets directly frozen into a solid form. -78.5 degrees centigrade is extremely cold, and handling dry ice without proper protection can be very dangerous – could cause frostbite / burns. The point being, it’s extremely cold.

Since it’s too cold compared to something at room temperature, even everyday objects at room temperature can make it vaporize. A simple metal coin at room temperature would feel like a hot pan to dry ice. So, when a coin is shoved into a piece of dry ice, it creates a funny sound, just like water would, on a very hot pan; or, you could say the sound be very much like a hot metal ball being dropped into a cold bath of water (the temperature difference being much less in this case, of course).

This is how it works: The metal piece at room temperature vaporizes some amount of carbon dioxide from the piece of dry ice when it comes in contact. There’s a pressure difference (Bernoulli’s principle) associated with this process and the gas tries to escape. This makes the metal vibrate very fast, creating that funny sound. This is how it sounds…

Metals work best because they have a good thermal conductivity. For the sake of trying it out yourself, if you have a piece of dry ice lying unused, you could dip a spoon in hot water and make it touch the piece of dry ice. A slightly warmer spoon will probably give you a better effect. And then the spoon will be singing…

Liquid Nitrogen Experiments

By Anupum Pant

Short of time and keeping up with a busy schedule, I looked around for something interesting to learn today and I found this cool video of very interesting experiments that were done with liquid Nitrogen on ScienceDump. There are 11 such experiments that are shown in the video…

The first one is a Liquid Nitrogen explosion, something like this professor did some time back. To demonstrate his students how Liquid Nitrogen expanded, he blew up a container of Liquid nitrogen to toss 1,500 ping-pong balls. [Video]

Is an Aeolipile, or a rocket styled jet engine made using liquid nitrogen A.K.A Hero engine. Liquid nitrogen heats up inside a container, expands and comes out of tiny orifices to create a jet that makes the container spin. A simpler version of it can be done using a ping pong ball (again). [Video]

The third one simply is a demonstration of what happens when you eat a biscuit dipped in Liquid Nitrogen.

Fourth one again is something you’ll have to see to get really impressed by what some solids at very low temperatures can do. A nice demonstration of something similar is done on this video. [Video]

Fifth one! Oh, the Leidenfrost effect. We’ve talked enough about it already. [Here]

Others are all pretty interesting too. The eight one probably takes the cake – brings back a dead creature to life, or does it…. But I won’t spoil them for you. Watch the video now…

The Coldest Place on Earth

By Anupum Pant

A couple of days back I wrote about the hottest place on earth. That made me think of how cold the coldest place would be. I was sure it’d be somewhere in one of the poles, but I wasn’t sure where exactly it was.

This is what Google said:

Aerial photograph of Vostok Station, the coldest directly observed location on Earth. The lowest natural temperature ever directly recorded at ground level on Earth is −89.2 °C (−128.6 °F; 184.0 K), at the Soviet Vostok Station in Antarctica, on July 21, 1983.

After a little more digging, I found that his was the old record. Turns out, the coldest place on earth now, not counting the laboratories, is still in the high ridges of the East Antarctic plateau close to Vostok station. It’s called the Dome B. And the coldest times happen when all the conditions are perfect.

When the conditions are right, the temperatures during winters can reach minus 92 degrees Celsius!

Hot Ice

By Anupum Pant

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For years we’ve been subconsciously conditioned to think of something cool when the word ‘ice’ is heard. But, does ice always has to be cool? How much more interesting, than water-ice, can ice be?

What is it?

The name: Hot ice isn’t solidified water, it isn’t anything even close to water. Neither is hot ice, hot. It is just a common name for Sodium Acetate Trihydrate. At room temperature, this substance looks like ice crystals and if heated, it starts turning into a transparent liquid. Since, the ice like crystals are formed at a relatively hotter temperature than water-ice, it is called hot ice.

Everything freezes. While metals ‘freeze’ at extremely high temperatures and carbon dioxide freezes at extremely low temperature, Sodium acetate freezes at 54 degrees centigrade. But, that is hardly anything interesting about it. There is more.

Touch water and turn it to ice

Think about water: Cooling water, beyond its freezing point without it getting solidified, can be done and it is called ‘super-cooling‘. This can be done by not letting water (distilled water) find any ‘nucleation points’ or simply by using an extremely clean tray to freeze it. Now, water remains in a liquid state despite being cooled under 0 degree centigrade. At such a state, if water is disturbed, say using your finger, a chain reaction starts and the water freezes almost instantly. But, doing it is tough.

Making hot ice at home – The same thing that happens with super-cooled water, can happen with sodium acetate. Touch the liquid sodium acetate and it magically turns to ice, it is indeed a fascinating process to watch (watch in the video below). And can be done fairly easily. Moreover, you are not at a danger of getting poisoned in any way. This is the reason it is used to make hot ice. It can be made at home using vinegar, baking soda and a steel vessel.

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.