Tag: demonstration

Chladni Figures

By Anupum Pant

If you take a surface, membrane with a layer of loose particles or certain liquids on it, you’ll see that these particles get arranged in beautiful patterns if the membrane is made to vibrate with varying frequencies.

This phenomenon has been known for a long time now, probably since the time when early human tribes used to put grains of sand on drums made of taut animal skin. Since then Leonardo Da Vinci and Galileo Galilei have been known to have observed this phenomenon by hitting or scraping a surface covered with visible particles and .

Later, with information gleaned from Galileo’s and Leonardo’s notes, in the year 1680, Robert Hooke, English scientist from the Oxford University, devised a simple equipment which demonstrated this effect much clearly. He made a glass plate covered with flour to vibrate with the help of a violin bow. And observed beautiful patterns.

Much later, Ernst Chladni explained these figures using mathematics, spread it all across Europe and made a lasting impression on The French Academy of Sciences. These patterns thus came to be known as Chladni figures.

Brusspup, a YouTube channel known for it’s amazing videos demonstrates these Chladni figures on video.

Today, this study, which makes sound and vibration visible to the naked eye, is called Cymatics.

Video: Change Blindness

By Anupum Pant

There’s so much happening around you that if your brain doesn’t have this ability to see and skip processing most of the useless information the eyes send it, you’d probably go mad in a day. That is change blindness. In that way, It is good for you. But you must not have realized how narrow your attention of focus can be. This video demonstrates it better than anything else.

By the way, when you watch the first clip where the camera pans with the Pacman, try focussing on the Pacman only. Or you won’t be able to appreciate the effect as much.

Prince Rupert’s Drop – Exploding Glass

By Anupum Pant

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What is it?

At first, a Prince Rupert’s Drop is an interesting yet harmless looking drop of glass with a long tail. It looks like a tadpole: [image]

It is no different from an annoyed person who refuses to let out his resentment – A slightest something might make him explode suddenly, but it isn’t easy to make him let it out. Confused? Read on…

Now, think of a glass drop that has immense amounts of potential energy stored inside it – It explodes (actually implodes) when the tail is disturbed, but it is impossible to hit it hard with a hammer and break it.

How?

A Prince Rupert’s Drop is formed when a drop of molten glass is suddenly dropped into a water bath. This quick cooling, solidifies the surface fast, while the inner part remains molten. Now, glass formed on the surface, being a poor conductor of heat doesn’t allow the inner part to cool quickly. When the inner part starts cooling, it tries to shrink and pulls the surface towards it. As a result, great amount of potential energy gets stored inside, in the form of stresses (stresses are seen using a polarized filter). This stored energy gets released when the tail is disturbed – It explodes into very tiny pieces of glass.

Toughened glass – a stronger variety of glass used in several places – also uses a similar technique to make strengthened glass.

On Wikipedia, a user asked about the possibility of utilizing the energy released from this explosion, being used to fire a bullet from a barrel. An interesting possibility, I must say.

The Name

Prince Rupert of Rhine did not discover the drops, but played a role in bringing them to Britain. He gave them to King Charles II, who in turn delivered them to the Royal Society for scientific study. Prince Rupert’s Drop was a widely known phenomenon among the educated during the 17th century – far more than now.

Watch it being explained better

Probably the best demonstration of this glass drop exploding is right here on the internet. Couple of months back, a YouTuber, Destin (Channel: SmarterEveryDay) posted a video demonstrating the physics behind it. He recorded  the progression of the explosive fracture using a hi-speed camera (at more than 100,000 frames per second) and calculated the speed of the fracture travelling through its tail (~ 1.5 miles per second). I’ve attached it below for you to watch.

Super-hydrophobic Surfaces are Unbelievable

by Anupum Pant

It is almost impossible to get a lotus leaf wet. If you try pouring water on it, you’ll see that it will form little beads of water and quickly roll out of the leaf. This happens because a lotus leaf is super-hydrophobic. Although, even your raincoat doesn’t get wet, it isn’t super-hydrophobic. Water sticks to on the surface of a raincoat. Super-hydrophobic surfaces don’t let water stick on it. But how do they manage to do that?

The science – Contact angle

Every time a liquid sits on the surface of a solid, the liquid drop forms an angle of contact as shown below. Things that don’t get wet have a contact angle greater than 90 degrees and the ones that get wet form an angle lesser than 90 degrees. The greatest angle is always less than 180 degrees. Theoretically, a perfect bead will form at that angle.

Super-hydrophobic surfaces are able to push this angle to as high as 175 degrees to form almost a perfectly spherical water droplet on the surface (due to very high surface energy). This ensures that as soon as water falls on it, it rolls away. The surface never gets wet.

Advantages

Imagine things never getting wet. How about a completely water resistant phone, a shoe that never gets dirty, shirts that repel ice-cream and wind-screens rolling away rain droplets like magic? All these things are possible, if they can be converted into super-hydrophobic surfaces. [They can be. Watch the video below]

Besides repelling water, these surfaces can also prevent formation of ice, resist corrosion and prevent bacteria from sticking to it. The possibilities are endless.

How to do it artificially?

Today, we have managed to develop several artificial methods to make almost any surface super-hydrophobic. Commercial services like NeverWet, HydroBead and Lotus leaf coatings are making a roar in the market by offering amazing promises. Normally, they use simplified spray coatings to convert normal surfaces to super-hydrophobic surfaces, so any one can use them, anywhere.