hot – Awesci – Science Everyday

Singing Sand Dunes

By Anupum Pant

I cannot say why you’d do it, but suppose you were on a hike to the top of a 120 feet sand dune in the centre of some desert, say near Al-Askharah, a coastal town in Oman. Unfortunately, it’s also the mid summer time, with 50 degree Celsius winds blowing at 50 miles an hour, and the dune you are climbing has a slope of 30 degrees. There’s nothing else (besides sand) to be seen or heard for miles around you.

The numbers are apparently perfect for a very eerie phenomenon to occur. And then the whole desert suddenly cries out a booming chorus of a very low hum (Like someone playing a very low note on the cello). What could have possibly caused that?

For ages such sounds in the midst of empty deserts have been bewildering people. Marco polo mentioned it. Charles Darwin also wrote about the “Bellower” in The Voyage of the Beagle. Moreover, until recently, even modern scientists weren’t sure what caused these sounds. It was only during the year 2009 that things started becoming clear when a group of researchers started experiments with sand on an incline in a laboratory environment.

The low droning hums, now as we know, come from within the sand dunes. The Sand particles are blown by the wind, causing an avalanche. As the sand falls across the 30 degree incline of the dune, they vibrate, synchronise and send the vibrations into the dune. The dunes pick up these tiny synchronised vibrations and amplify them, causing the low droning hum; coherent enough to resemble musical notes.

This only happens at few places around the world. In Morocco the dunes cry out an echoing hum of 105 hertz. Whereas in Oman the sands create a mixture of frequencies ranging from low 90 to slightly less low, 150 hertz. Something similar is also heard in the death valley. The video explains…

The Hottest Place on Earth – Not Death Valley!

By Anupum Pant

For years I’ve known that the death valley was the hottest place on earth. Of course, not counting the lava, laboratory furnaces, hot springs and other such smart-ass answers, the death valley has always been, in textbooks and beyond, the hottest place on our planet.

On July 10th 1913, the temperature there was measured to be around 56.7 degrees centigrade. Nowhere else has the mercury risen to such high levels since then. Or so we thought…

Until, like always, a science channel from YouTube – MinuteEarth – decided to dive in a little deeper.

This is what the weather statistics do when they measure the temperature – The temperature outdoors are measured in shade at about 1.5 meters above the ground. Of course they had a standard procedure set to do that, and there must be a solid reason for that.

But, practically, who are we kidding. Anyone who has been on a beach, barefoot on a sunny day knows how hot the surface of sand can get in the sun, right?

The data from NASA’s satellites equipped with spectroradiometers has a different story to tell. A place somewhere in the Lut desert in Iran is the winner. The temperature averaged in a 1 square kilometre by the satellite shows that temperatures here have reached a whooping 70.7 degree Celsius. The place is somewhere inside the blue circle I made on Google maps.

You could literally cook eggs in the open there. Anyway, that isn’t totally new. Mr. Sargunaraj claims to have cooked an egg on the streets of Tirunelveli District in Tamil Nadu, India too. And I’ve also seen a video of a restaurant serving eggs cooked in the open (without fuel).

Water vs. Red-Hot Nickel Ball

By Anupum Pant

Let me just not say anything before I make you watch this video today:

In the video, a Nickel ball is heated using a torch and is dropped into a bowl of water. As the hot ball touches water for the first time, it makes a certain “Ping” sound. It enters the water and gets covered in a bubble sort of thing. As it cools and the bubble is lost, that “ping” sound comes back again. The “Ping” repeats several times and is fun to hear a metal ball do that!

So much fun that the good guys on Reddit even made a couple of ringtones out of it. Download the longer one here. And the shorter one for notifications here.

Why does it form a Bubble cover?

This happens because the metal that is dropped into water is extremely hot and makes the water around it vaporize. The vapor formed around the ball acts as an insulator and doesn’t let the water touch the metal ball. This is the same effect that lets dip your hand in molten lead or Liquid Nitrogen without getting harmed by it. The same thing happens when you drop water on a hot pan – it dances.

This effect is called the Leidenfrost effect and I’ve covered it in an article before…

I’m not sure what exactly causes the “Ping” sound. If you know or have any theories, please tell me in the comments below.

CrashCourse in Quenching

Well, if I’d have wished to piss you off with jargon, I’d have said: “You just watched a hot Nickel ball being quenched in water”

Yes, quenching. Quenching is the name for making a hot metal cool very quickly. It is pretty interesting to know why some one would, with great effort, heat a metal, and then choose to drop it in water to cool off!
Cooling a hot piece of metal very quickly makes it extremely hard. So hard, that the same process is used to make the hard edges of swords that don’t get damaged even if they are used to cut metal!

There is so much more I wanted to write about the process, but I feel this isn’t the right place for it. Let me leave it for some other day.

Dancing Drops of Water and Dipping Hands in Molten Metal

By Anupum Pant

When you sprinkle water on a hot pan, you’ll find that the droplets start dancing on the surface, as if there was no friction at all. From far, this effect looks a lot like water droplets on a lotus leaf (a super-hydrophobic surface). But, the physics behind this phenomenon is completely different. Read on to find out what is the mystery behind these dancing drops of water.

The Leidenfrost Effect

Why does this happen?
Unlike the drops on a lotus leaf, this happens at a particular temperature for a specific liquid. Different kinds of liquids display this effect at different temperatures.
For water, at a temperature when a small amount of water in contact with the pan gets heated enough to form a thin-film of vapor below the drop, water is no longer stuck on the pan (water sticks to some surfaces due to low surface tension). The drop has a thin vapor film below it which enables the drop to move around on the film. The formation of this vapor film is a continuous process, till the whole drop turns into water, one film at a time. This is called the Leidenfrost Effect.

Some liquids like liquid Nitrogen are extremely cold. At normal room temperature, they start boiling. A normal room’s floor is like a hot pan for liquid Nitrogen. So, it forms these dancing drops on a floor which is just at room temperature. You can try this yourself – If you can find some liquid Nitrogen, you can simply drop it on the floor and watch droplets moving effortlessly. They won’t stop moving!

Dipping hands in Liquid Nitrogen

The temperature of liquid Nitrogen is around -195 degree centigrade. It is one of the coldest substances and is used with extreme caution in industries and laboratories. If it touches you, your skin can easily get burnt. Yes, burnt – at extremely low temperature. It could probably also make the dipped limb useless for life. So, you shouldn’t try stuff with liquid Nitrogen at home.

But, it turns out, you can safely dip your hand in it for a small amount of time and return unharmed. Thanks to the Leidenfrost effect. Our hot-pan like hand – for cold liquid Nitrogen – makes a thin film of vaporized Nitrogen around the whole hand. This film, protects our skin from the ill effects of extremely cold temperatures. Still, there is no reason for you to try this. It has been done already.

The crazy duo from Myth Busters tried this with molten lead. It worked! They, of course had to wet the finger with water – for the vapor film formation.

Water flowing uphill

Recently, an undergraduate research student group from the University of Bath found out a way to manipulate the movement of water on a specially designed surface, using this phenomenon. They found that machining ridges on the surface (and heating it) would make the thin vapor films under water droplets move in such a way, that they could use it to propel drops against gravity. They were able to demonstrate this by showing water moving uphill on a slope. It is enthralling to see it for yourself. I’ve attached their video below.