Bricks Which Are Lighter Than Air

by Anupum Pant

What would smoke look and feel like, if you could solidify it?

Aerogels

Although, first made in 1931, Aerogels are relatively newer materials and a tremendous amount of research is being done on them everyday. Lightest solids ever, Aerogels weighing about seven times lesser than air have been made. Their extreme properties have given a fascinating field of interest to students and scientists. [Read the last paragraph]

How are they made?
Aerogels, also known as solid smoke or frozen smoke are extremely light materials. They are made by a process called sol-gel process which involves removing all the moisture from a specially made gel (Hypercritical Drying). Although the procedure may sound simple, there is a lot of technology involved in making them. Moreover, practically usable Aerogels which can endure moist conditions and high stress conditions are much more challenging to make. Also, it is very expensive to make them. [They can be made at home – with costly equipment of course]

Why is it so light? 
The whole lot of porosity left inside due to drying of the gel is what makes it so light. You can think of them as a sponge which is hard like pumice. But, when you think of a sponge, remember that mostly Aerogels aren’t very resilient. That means, unlike sponge they won’t get back into the previous shape after they’ve been pressed a lot. They are much sturdier/tighter than sponges. A small (not very small; due to very low density they occupy large space) piece of Aerogel weighing just 2 grams has been shown to hold a 2.5 kg brick without deforming. Poorly made Aerogels, on the other hand can also not be very sturdy. They would deform with a hard press of a finger and stay deformed.

How light are they?
Agreed, they can be lighter than air, but the practical mass varies greatly. And they don’t float in air because, with air present inside them, they are slightly heavier than air (weight of air inside + solid material), but can be made to float in air by replacing the air inside it with Hydrogen or Helium. Their lightness and density is completely dependent on the amount of porosity included during the fabrication – which can be controlled. Also, the kind of gel used to make it, affects the weight of the final block. So a block with 3 feet in length, breath and height can weigh anything from 1 kg to just 160 gm.

Aerographite, a carbon Aerogel made by German material scientists from Kiel University and the Hamburg University of Technology, was said to have weighed only 0.2 mg per cubic centimeter. It was 5000 times less dense than water and 6 times lighter than air (counting only the solid material’s weight of course). [Published Paper]

Graphene Aerogel: As if that wasn’t enough, recently, Chinese material scientists developed a lighter material than Aerographite. It was based on Graphene. A Graphene Aerogel; seven times lighter than air. This one, unlike other silica Aerogels, can recover like a sponge after getting deformed. [Published Paper]

Other Properties

Aerogels exhibit various other desirable properties which make them useful for a myriad of applications [See the Wikipedia Article]. For instance, they are very good insulators of heat. A nicely made Aerogel block which is just under a centimeter thick can protect things from a direct flame. Other desirable properties are high surface area, high thermal and acoustic resistivity, low dielectric constant, and low refractive index.

Aerogels absorb water or moisture from the air and even from human skin easily. Handling them with bare hands can cause blisters. But, the ones which repel water have been made successfully by altering fabrication parameters. Also, if particles of it are inhaled, it can cause problems. Hence, hand gloves and respiratory masks are used to handle them.

I want to study interesting materials like these

If you think Aerogels and Wolverine’s claws are interesting things. You can make a career in researching materials like these by making a foray into Materials Science and Engineering. Most good universities offer a course in it. It is a budding field, growing at a rapid pace with loads of opportunities waiting for you.

How Loud Can it Get?

by Anupum Pant

Wives and moms can scream really well. But is it loud enough to inflict physical pain? Can sounds get louder than a nuclear bomb? How much damage can a loud sound cause? How about mass extinction? Read on to find out the answers.

What is sound?

Sound, as most of us know is a longitudinal, mechanical wave. That means, it is just a series of pressure changes [compressions and rarefactions] in a particular medium. So, the property of sound is as good as the medium it uses to travel. For instance, sound cannot travel in a vacuum due to the absence of any medium, but it can travel much faster in solids than in air. That is the reason you can’t hear someone talking in space (yes, movies that show loud explosions in space, lie). Also, the faster speed of sound in steel rails is exactly the reason why, you can tell a train is approaching, if you stick your ears to the rails (do not try this on electric rails).

Two of the fundamental parameters that describe a sound wave in numbers are pitch and amplitude. Pitch is measured in hertz – we’ll talk about it some other day. But, the amplitude of a sound wave determines how powerful it is; greater the amplitude, louder the sound. The loudness of sound is measured in Decibels (abbreviated dB).

More about decibel scale

Like most other linear scales, Decibel isn’t as easy to understand. A 10 point rise in the dB scale can be visualized as a 10 times increase in the loudness. Adding dB levels of different sound sources also doesn’t really work, the calculation is much more complicated; the resultant loudness depends on the coherency of the source [See this decibel addition applet]. Also, the perceived loudness is obviously lesser as you go away from the sound. Normally, a decibel scale ranging from 0 dB to 130 dB is enough for measuring the loudness of most things. But, things can get louder…much louder.

To get an idea of the decibel scale: 10 dB is 10 times more powerful than 0 dB, not 10 points greater. Similarly, 20 dB is 100 times more powerful and 140 dB is 100,000,000,000,000 times more powerful than a o dB sound.

0 dB is the loudness of near silence (a mosquito 10 feet away), while 120 dB is the loudness of a loud car horn heard from 1 meter away. Humans can hear sounds starting from 0 dB. But it can be quieter than 0 dB [the world’s quietest room]. It measures record setting -9 dB and can literally drive you crazy. In fact, the longest someone stayed in that room was for 45 minutes.
On the upper side of dB spectrum, a whisper is around 15 dB, conversations range from 40 – 60 dB and a jet engine measures 130 dB on the decibel scale. Like I said before, the perceived loudness depends on your ear’s distance from the source, so the loudness of a lawnmower can range anything from 90 dB to as much as 110 dB if you stand 3 feet away from it. [see the Decibel chart]

90 Decibels or a sound as loud as only a raised voice can cause gradual hearing loss (Refer to the hearing safety chart here). While 140 dB can cause physical pain. After 150 dB (firecracker) sounds can be felt in the form of shock waves. The pressure difference they cause in the medium can actually be felt by your body.

Beyond Decibels

Since the loudness depends on the medium, the maximum loudness a medium can propagate is dependent on its density. Our atmosphere can do nothing more than 190 dB, that, by the way, is enough to make you deaf or cause death. Sounds in water can get louder. A pistol shrimp is able to create a 200+ dB sound at 97 km/h to stun or kill its prey by snapping claws really fast. This is a very short lived pulse which doesn’t carry enough energy to do us any harm.

For events like the Saturn V launch, volcanic explosion, nuclear bomb explosion, earthquakes, star-quakes the concept of sound doesn’t really apply anymore. They are measured in terms of the shock wave they produce using the Richter scale. On this scale, 9 means total destruction (8.2 was measured during the explosion of the largest bomb ever, Tsar Bomba). An earthquake or earthly event measuring 10 has never been observed.

However, in the universe beyond earth, the starquake on the magnetar SGR 1806-20 registered 22.8 to 32 on the Richter scale. The magnetar released more energy in one-tenth of a second than our sun has released in 100,000 years. An event which thankfully took place 50,000 light-years away from earth. Had it been even 10 light-years away, the energy released would have wiped off life on earth. [read this BBC article for more information on this event]

 

The Purpose of Sleep – Theories

by Anupum Pant

Did you know?

  • You can live longer without food than you can live without sleep.
  • On an average, a person sleeps for 1/3rd of his life. That means if you are 30 years old, you’ve slept for 10 years already.
  • The world record for the longest span remaining awake is 11 days. The record was set by 17-year-old Randy Gardner in 1964 when he was awake for 264 hours and 12 minutes. (Don’t try this)
  • If it takes you less than five minutes to fall asleep then very likely you are sleep deprived. It should take about 10 minutes normally.
  • You can lose up to 2 grams every minute while sleeping. That comes to about a lost Kilogram at night.

What is Sleep?

Everybody sleeps. On an average, everyday, a bat sleeps for 15 hours while just 3 hours are enough for a Horse to feel rested [How much do animals sleep – chart]. Dolphins can sleep with half of their brains active and even the smallest of worms need sleep. But, till date, scientists haven’t been able to reach a consensus on why we actually do it?

Sleep can be understood as a life sustaining activity. It can be compared to another of our important activity – eating. These strongest of the human urges – eating and sleeping – serve a nearly common purpose – quell the urges; just as eating relieves hunger, sleeping relives sleepiness.

While it is true that we may have not been able to spot the primary purpose of sleep, years of research hasn’t gone wasted. With time, we have learnt a lot more about sleep than we used to know 50 years back. There have been hundreds of practical and impractical theories on why we sleep. I’ve mentioned a few of the realistic ones here.

Purpose of Sleep – Theories

Inactivity Theory:

According to this old theory, sleep evolved out of the need to be safe. It suggests that inactivity at night is an adaptation that serves as a survival mechanism. It functions as an activity which would keep an animal safe during the time it is most vulnerable e.g. Humans are vulnerable at night because they don’t see well in dark.

This theory is easily countered using the argument: Being conscious and still, is much better way to stay safe than lying unconscious and still.

Energy Conversation Theory:

It suggests, the main function of sleep is to reduce the demand and consumption rate of energy at times when searching for food isn’t an efficient option. Some believe, that this theory is a part of the inactivity theory. But, unlike the inactivity theory, this theory has been bolstered by various experiments which prove that the consumption of energy is reduced when an organism sleeps.

Restorative theory:

It explains sleep as an opportunity for a body to rejuvenate in terms of muscles, tissues, proteins, cells and growth hormones. Also, during sleep, the body clears an accumulated molecule called adenosine from the system, and makes us feel alert when we wake.

recent study also seems to support the restorative theory in a fresh manner. It says, brain accumulates toxins [like beta amyloid] while it is awake. The concentration of such toxins keeps increasing during waking state. The study observed an increased activity of spinal fluid being pumped into the brain in rodents (hasn’t been studied on humans yet). This spinal fluid functions as a medium to pump out toxins from the brain. This theory could be a breakthrough in the study of causes and prevention of Alzheimer’s as it is known that toxins like beta amyloid cause the disease in humans [How beta amyloid causes Alzheimer’s].

Brain Plasticity Theory:

According to this, sleep plays a critical role in brain development. Infants (age when the brain develops the most), for example, sleep for about 13 – 14 hours every day. On the other hand, the poor ability to learn and perform tasks due to the lack of sleep explains the role of sleep in adults. Since, It has been proven that brain is highly active during sleep, this theory remains the most plausible one in being able to state one of the functions of sleep.