Tag: physics

Posted in Science & Nature

Thuder And Lightning

Posted on by Jinavie

The best or worst part (depending on your preference) about a dark and stormy night are the majestic flashes of lightning and booming thunder. Most people confuse the two terms, typically using “thunder” to describe both, but technically thunder is the sound produced by lightning, which is the flash of light. Lightning occurs when dense clouds become electrically charged due to the collision of water molecules. As charge builds up, the cloud becomes negatively charged. The negative charge becomes so intense that it begins to push electrons towards the surface of the Earth, creating a positive charge. Electricity always flows from a negative charge to a positive charge through a medium. The intensity of charges causes the air to become ionized (plasma), making it suddenly conductive and allowing the electricity to flow from the cloud to the ground. This is seen as a flash of intense light. As the electricity travels through this channel of air, it superheats the air and causes a massive expansion of air, much like an explosion. This creates an intense shockwave burst, producing a sound that we call thunder.

Lightning is a deadly force of nature. It clocks a peak voltage of somewhere between 30 million to billions of volts – far exceeding the electricity that can be generated by humans. When a lightning bolt strikes a human, it has a mortality rate of between 10~30%. The two effects of lightning on the human body is electrical shock and heat. As lightning flashes over the skin to reach the ground, it leaves a striking pattern known as Lichtenberg figures (see below), showing the path of the electrical breakdown. The intense electrical burst can cause loss of consciousness, arrhythmia or sudden cardiac arrest. The heat generated by the electricity can cause severe burns both externally and internally. It can literally fry internal organs causing permanent damage to the heart, lungs and brain. Neurological symptoms such as amnesia, confusion, sleep disturbance and chronic pain have also been reported. Strangely, there are also reported cases of lightning curing ailments such as blindness, deafness and baldness.

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Because lightning is light and thunder is sound, one can calculate how far away lightning struck using the time between the lightning flash and the sound of thunder. Sound travels at 340m/s, so by multiplying the number of seconds between the lightning and thunder by 340, you can deduce the distance in metres. For example, if you see a lightning strike and then hear thunder after 7 seconds, the lightning must have struck 340m x 7s = 2380m = 2.38km away.

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Posted in Science & Nature

Brazil Nut Effect

Posted on by Jinavie

Have you ever bought a bag of mixed nuts and noticed that Brazil nuts tend to be on the top of the pile? If you put nuts of various sizes in a bag and shake it, you will see that the larger nuts (such as Brazil nuts) will rise to the top slowly. This is strange as common sense dictates that heavier objects sink to the bottom. The strangest thing? No one knows exactly why this happens.

However, there are some persuasive theories. It has been suggested that the so-called Brazil nut effect is due to a phenomenon called granular convection. Convection is usually used to describe the movement of gases and liquids, where heated particles are more active and lighter, thus rising to the top. As the particles rise, they cool down and fall back to the bottom, creating a current. It seems to be that the same can be applied to solid particles, such as nuts. When the jar or bag of nuts is shaken, a vibrational force is applied. Nuts in the middle are pushed upwards by the vibration, with smaller particles filling the gap below. Once the nuts reach the top surface, the vibration pushes the nuts towards the side, where they are then pushed back to the bottom. However, larger nuts like Brazil nuts are too big to fit in this downward current so they stay on the top. 

The Brazil nut effect is not exclusive to Brazil nuts. A similar phenomenon can be seen with any large particles surrounded by smaller particles, like pebbles in sand or coffee beans in ground coffee. The theory of granular convection has still not been fully understood, with various factors such as nut density and air pressure seeming to play a role.

Posted in Psychology & Medicine

Viscera: Lungs

Posted on by Jinavie

(Learn more about the organs of the human bodies in other posts in the Viscera series here: https://jineralknowledge.com/tag/viscera/?order=asc)

Everyone knows that we need oxygen to survive. The way we get oxygen from the atmosphere is through our lungs – the organ where gas exchange takes place. The pair of lungs take up a large proportion of the chest cavity and they link up with each other to form the trachea (windpipe). The left lung is slightly smaller to accommodate for the heart.

The lung is extremely soft and light, so much that it floats on water. It is essentially made up of an intricate tree-like system of airways, which become narrower and narrower as it divides out from the trachea. Since every airway divides up, the number of airways increases exponentially. Every bronchiole (small airways) ends in a bubble-like sac called an alveolus. Because of the sheer number of alveoli, the lungs actually have a total surface area the size of a tennis court. To picture this, scrunch up a piece of newspaper into a ball to pack a large surface area into a small space. The massive surface area allows for enough gas exchange to occur to give us the oxygen we need and excrete all the carbon dioxide we produce.

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When we take a breath in, the chest cavity expands and stretches the lungs in all directions because of the negative pressure (like a vacuum). Air fills the airways all the way to the alveoli. The alveoli are extremely thin; so thin that the oxygen in the air effortlessly seeps through into the blood vessels that surround the alveoli. On the other hand, carbon dioxide seeps out of the blood into the alveoli, which is then breathed out as the muscles of your ribcage contract to force the air out. This process is called gas exchange and is driven by diffusion – the movement of particles from an area of high concentration to an area of low concentration (like how dye spreads throughout water).

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It is well-known that smoking is bad for your lungs. This is because of two major reasons: COPD and lung cancer. COPD (chronic obstructive pulmonary disorder) is when your lungs become so damaged by smoking that they cannot function, leading to hypoxia (lack of oxygen) and hypercapnia (excess of carbon dioxide). Smoking causes inflammation in the lungs, which causes airways to shut down from swelling and mucus, while destroying the fine walls of the alveoli. This causes the alveoli to thicken from scarring and less elastic due to the destruction of elastic tissue. Ultimately, the lungs become hyperinflated as the patient cannot breathe out air properly and the lungs are not elastic enough to return to their original shape and size. Ergo, the patient becomes progressively breathless, gasping for breath as they suffer a sensation of impending death as the carbon dioxide level builds and the oxygen level falls.

Posted in Science & Nature

Natural Design

Posted on by Jinavie

We look around the world we live in and marvel in all its complexity and grandeur. But Mother Nature focusses on one thing when it comes to design: efficiency. That is to say, that nature strives to design things that will do the job best. For example, stars and planets are always round because a sphere is the most effective way to get all the mass as close to the planet’s centre of gravity as possible (a process known as isostatic adjustment). The wings of a bird have evolved to maximise the thrust generated at the least energy cost, while the sleek, teardrop body shape of fish allow for them to slip through water with minimal resistance. One of the best examples of nature coming up with the best design solution is beehives.

If you look closely at a beehive, you will find that it is made up of tiny hexagons. Each hexagon is a room that a bee can fit in and the walls are made from wax. The interesting thing about hexagons is that it has many properties that make it the ideal shape in construction.

Firstly, hexagons can fit together perfectly to tile a plane, meaning that bees can tile thousands of columns without wasting any space. The little columns even end in a unique pyramidal shape that allows them to tile up nicely with each other at the centre.

Secondly, a hexagon has 6 rotational symmetries and 6 reflection symmetries, making it very easy to tile as every bee will know what orientation to build their cell in using the side of any cell as a reference.

Lastly, in a hexagonal grid each line is as short as it can possibly be when tiling an area with the smallest number of hexagons. Therefore, bees can use much less wax when constructing hives, while achieving remarkable strength as hexagons gain lots of strength under compression. This design also allows for the maximum amount of honey stored in each cell.

Bees have mastered this architectural feat not through physics and mathematics, but through evolution – the driving force of nature. Over millions and millions of years, various types of bees will have experimented with square-celled hives or triangular-celled hives, but they could not survive as long as the hexagonal-celled bees because their hives were less efficient. This is exactly why nature is so good at coming up with the best solution to a problem. Because in nature, the best solution to the problem an environment offers is rewarded with survival.

Posted in Science & Nature

Cow Modelling

Posted on by Jinavie

There is a farmer who is unhappy with the milk production from his dairy farm. To rectify this, he writes to the local university asking for advice. A theoretical physicist responds to the request and visits the farm. He then takes many measurements such as the size of the cow and proceeds to do some calculations. After finishing all of this, he tells the farmer: “I have a solution, but it only works for spherical cows in a vacuum.”

The point of the joke is that in science, models are frequently used to simplify reality. Because there are infinite amounts of variables, it is impossible to predict anything unless the scenario is simplified through certain assumptions and removal of factors. For example, many physics principles make assumptions such as not accounting for air resistance. Occam’s razor states that if you shave away all the complex details, the simplest answer remains. But perhaps we oversimplify some things?

Posted in Science & Nature

Doppler Effect

Posted on by Jinavie

Have you ever noticed that when a car or train speed past you, the sound it makes changes in pitch depending on where it is? For example, imagine a train loaded with a marching band. You watch the train come closer and closer to the station where you wait, while the band plays a single note. As the train approaches, the pitch of the note gets higher and higher. The train does not see you and races past the station. As it gets further from you, the note played by the band becomes lower and lower in pitch again. If you cannot imagine this, the next time you see a police car or ambulance racing past you, carefully listen to the sound of the siren.

This change in pitch is called the Doppler effect. The Doppler effect is defined as the change in frequency of a wave (such as sound) for an observer moving relative to the source. It occurs because of the nature of waves. When the source of the sound is still, sound waves ripple out in all directions at a uniform speed. But when the source begins to move, the waves in front of the source begins to bunch up as the source moves with the wave, shortening the distance between each successive wave. As the waves bunch up, the frequency of the sound wave increases, causing a stationary observer to hear it as a higher pitch. This is essentially the same as the waves in the front of a moving boat being bunched up.

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The Doppler effect is very useful as it lets the observer measure the speed of the moving object from the amount of “shift” that occurred in the measured wave. This is how speed guns work. Astronomists can use the shift in colour of a star to measure the speed at which it is moving away from or towards us (known as a blue or red shift respectively). In medicine, the Doppler effect is used to visualise the flow of blood in the heart or through vessels on an ultrasound.

In modern society, life gets extremely busy and we have to move quite fast to catch up with it. But like with the Doppler effect, sometimes moving too fast can distort things. You might lose track of what your hopes, dreams and priorities are. People might see a distorted version of who you really are and say that you have “changed”. So no matter how busy you are and how fast the world spins on, remember that it is okay to slow down every now and then just to get a clear picture of where you are, who you are or what you are doing. For in the wise words of Ferris Bueller: “Life moves pretty fast. If you don’t stop and look around once in a while, you could miss it”.

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Posted in Science & Nature

Hammer And Feather

Posted on by Jinavie

What would happen if you dropped a 1kg ball and a 10kg ball at the same time from a high building? Most people would think that the 10kg ball would obviously fall faster and thus hit the ground faster, but the truth is they would fall at exactly the same time. The reason for this is that the force that accelerates a falling object is gravity, which on Earth is constant at 9.81ms-2. This means that no matter how heavy the object is, they will always accelerate by 9.81 metres per second per second. This was hypothesised by Galileo Galilei, who came up with the thought experiment of dropping two balls of different mass from the Leaning Tower of Pisa (there is debate as to whether he actually performed the experiment). The theory was later solidified by a certain Isaac Newton, who devised the laws of universal gravitation and the three laws of motion.

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However, if the two balls were dropped from an extremely high place, they may land at different times as mass affects the terminal velocity – when the force of gravity equals the force of drag caused by air resistance, leading to a constant velocity. A heavier object will keep accelerating to a greater velocity than a lighter object, which would have reached terminal velocity before the heavier object.

One place where this will not happen is in a vacuum where there is no drag force. To prove that the hypothesis that two objects of different masses will fall at the same time in the absence of air resistance, Commander David Scott of the Apollo 15 moon mission took a hammer and a feather with him. Once he landed on the moon, he dropped the hammer and feather in front of a live camera, showing that the two landed at exactly the same time. He thus proved that Galileo’s conclusion from two hundred years ago was in fact correct.

Posted in Science & Nature

Banana Equivalent Dose

Posted on by Jinavie

No form of energy has been more feared or creatively explored in science fiction (e.g. Godzilla) as radiation, yet the layman tends to know little about the actual properties and effects of radiation. The word “radiation” is commonly associated with things like Chernobyl, mutation and cancer. However, most people only know that radiation is “bad” while not knowing exactly how and why it is dangerous. Radiation is essentially high-frequency light which can deliver a large dose of energy (just like how microwaves cook food and sunlight can burn paper when focussed through a magnifying glass). When this high-dose of energy passes through living organisms, it damages the DNA in cells, potentially causing irreparable damage. This can lead to mutation and disruption of cell division (which can lead to cancer) or cell death (which is why radiation is ironically used to kill cancer cells).

The more technical question is “how much” radiation is harmful. For example, how much more dangerous was the Chernobyl incident compared to an x-ray? Like many other things in science, radiation is measured using an internationally universal unit called the Sievert (Sv). The radiation received from standing next to the Chernobyl reactor core after meltdown was 50Sv, while a chest x-ray is 20μSv (1000μSv = 1mSv, 1000mSv = 1Sv). Therefore, the Chernobyl incident could be considered to be as strong as 2.5 million chest x-rays. Although there is great variation, it is considered that a dose of 400mSv can cause symptoms of radiation poisoning, while 4~8Sv of radiation will lead to certain death.

Fascinatingly, radiation is not an uncommon thing. Radiation is all around us, with an average person receiving about 10μSv of background radiation per day just by living on Earth. Ergo, two days of walking around gives you the same amount of radiation as a single chest x-ray. A CT scan gives out a significantly greater dose of radiation at about 7mSv (approximately 350 x-rays or a year’s worth of background radiation).

However, the Sievert is a unit that is difficult to understand. Thus, some scientists devised a clever, humorous equivalent unit called the banana equivalent dose (BED). Bananas contain a certain amount of radioactive isotopes (radioactive potassium), making them technically radioactive. A banana contains 0.1μSv of radiation. Ergo, a chest x-ray is the equivalent to eating 200 bananas, a CT scan is 70000 bananas, while the Chernobyl incident gave people nearby a dose of roughly 500 million bananas.

The banana equivalent dose is a rather useful (and hilarious) way of comparing the danger of radiation from different sources. The next time you go to hospital for an x-ray, just picture 200 bananas being shot through your chest.

Posted in Science & Nature

Folding Paper

Posted on by Jinavie

Take any piece of paper and fold it in half. Then fold it in half again. Chances are, you will not be able to fold the paper more than seven times. Try it. No matter how thin the piece of paper is, it is extremely difficult to fold a piece of paper in half more than seven times. The reason? Mathematics.

A standard sheet of office paper is less than 0.1mm thick. By folding it in half, the thickness doubles and becomes 0.2mm. Another fold increases it to 0.4mm. Already, the problem can be seen. Folding a paper in half doubles the thickness, meaning every fold increases the thickness exponentially (2ⁿ). By seven folds, the thickness is 2 x 2 x 2 x 2 x 2 x 2 x 2 = 128 times the original thickness. This makes the piece of paper so thick that it is “unfoldable”.

Another limitation is that folding the paper using the traditional method means the area also halves, decreasing exponentially. With a standard piece of paper, the area of the paper is so small after seven folds that it is mechanically impossible to fold it. Furthermore, the distortion caused by the folds is too great for you to apply enough leverage for folding the paper.

Could these limitations be overcome by using a larger piece of paper? Sadly, no matter how large the piece of paper, it is impossible (or at least extremely difficult) to fold a piece of paper over seven times. This has been a mathematical conundrum for ages, until it was solved in 2002 by a high school student named Britney Gallivan. Gallivan demonstrated that using maths, she could fold a piece of paper 12 times. The solution was not simple though. To fold the paper 12 times, she had to use a special, single piece of toilet paper 1200m in length. She calculated that instead of folding in half every other direction (the traditional way), the least volume of paper to get 12 folds would be to fold in the same direction using a very long sheet of paper.

Mathematics, along with science, is what makes something that seems so simple, impossible.

Posted in Psychology & Medicine

Reaction

Posted on by Jinavie

If you were walking along the street and found a bird lying on the ground, how would you react? You would probably poke the bird to see if it is alive. We have a peculiar habit since we are children of poking living things that we see for the first time. Through poking, we discover whether it is alive or dead, soft or hard, slimy or furry, docile or aggressive.

Prompting a reaction and observing the reaction is a surprisingly useful way of learning. In chemistry, we react an unknown substance with other chemicals to discover its identity. In medicine, we stimulate parts of the brain with electricity to discover what each part does. In physics, we build giant accelerator to crash particles together to find out their constituents and properties. If you fell into a cave so dark you cannot see even one foot ahead of you, the best way to find out if there is a wall or a hole or water ahead of you is throwing a rock in that direction.

This principle can be applied to psychology. To learn how people around you behave, provoke them. Human beings are extremely sensitive to stimuli and even when they consciously try to hide it, they will subconsciously react. If you keep (subtly) poking the person, you will soon be able to predict how they will react to something, what actions they will take, and you may even discover what is on their mind.

We cannot see the wind, but we can infer that it exists because the leaves blow. The best way to prove something that you cannot see inducing and looking for reactions.