Home, Science, Science Concepts

Nuclear Fusion- Does Our Future Depend On It?

Hi Guys,

I’m sorry for the long pauses in between posts, I’m busy with my third year in secondary school and I simply do not have as much time to write these posts anymore. This year i will be participating in a lot more activities (Science Mentorship Programme, completing my novel etc.). Blogging has been really fun and i really wish that i can make time to do more of these blogs. However, it’s really tough to pull myself to blog after a long day at school. Furthermore i try to make my posts as good as possible and this makes blogging take even more time. In fact i have been working on this very post since mid-December. I will definitely continue to post more, but the frequency of posts will have to be reduced. I simply can’t bring myself to post something that I myself feel is of low quality.

Okay, enough talk, lets get back to the main topic of this post.

I have been thinking about fusion lately after watching a TED video regarding the issue. Fusion has always been something extremely fascinating to me ever since I learnt about it. (and yes, I am going to keep referring to nuclear fusion as fusion.)

When we, as a human race, try to solve engineering problems, we usually turn to nature to give us inspiration. From the minesweeper inspiring tumbleweed to lotus leaves that have inspired us to create hydrophobic surfaces, nature has helped us solve our issues again and again. Fusion is one of those instances where we have taken inspiration from nature, but this time instead of seeking that inspiration from living beings on earth, we have taken that inspiration from the skies.

When we gaze into the sky at night we see stars, hundreds, thousands, even millions of them. When we look into the sky in the day, we see the sun. All these majestic things that fill the sky are all powered by nuclear fusion, the very thing we seek to be able to utilise some day. The intense light and heat coming from the sun and the stars are all produced by tiny nuclei colliding into each other; resulting in part of their mass being converted into energy.

The amount of energy produced is insanely huge. How huge? To answer this question we must look at one of the most famous equations in human history. E=mc^2. E equals m c squared. The energy-mass equivalence formula. Whatever you call it. Developed by the famous Albert Einstein, this short equation reveals the power of nuclear power. Here are the definitions of the terms in the formula:

E- Energy

m- Mass

c- the speed of light

Well if you consider the fact that the speed of light is 300,000,000 m/s (or 300 million m/s) )and after squaring the value you get 90,000,000,000,000,000 (or 90 trillion), you can convert 1 kilogram of mass into enough energy to keep the entire world running for 6 seconds. Well, that ain’t bad considering we burn 9,825,414,830 liters of oil in a day. That’s over 9 billion liters of oil and oil only.

So yes, fusion is powerful. Very powerful. So how does it work? In the stars, intense heat and pressure (and sometimes with a bit of luck), fusion occurs. The heat causes the atoms in the stars to move extremely quickly, this causes the atoms to collide into each other very frequently and with extreme speed and force. The pressure forces them closer to each other, further increasing the frequency of the collisions. With these ingredients, together with some nuclear fuel, the beautiful process occurs, generating large amounts of heat (the energy that is released from the process). PhdComics has made a video explaining the process of fusion.

Fusion makes use of nuclear fuel with small nuclei such as hydrogen and helium. The process can only fuse atoms up to iron. Atoms larger than iron are too heavy to be fused any further. This is opposite of nuclear fission where nuclear fuel with large nuclei are used. After iron, to produce larger nuclei, a supernova has to occur for heavier elements to form.

I recently found this joke on the website SGAG. To those Singaporeans out there, you should probably understand this joke:

fusion joke

 

The above is in fact true! The reason why supernovas are able to allow larger atoms to form is due to the fact that the force of the explosion generated by the supernova is so great that the iron actually manages to fuse into larger nuclei. Through the explosions of millions or even billions of supernovas, the atoms essential for life were formed.

You could say that you were born from a dying star 🙂

“The most astounding fact is the knowledge that the atoms that comprise life on Earth, the atoms that make up the human body, are traceable to the crucibles that cooked light elements into heavy elements in their core under extreme temperatures and pressures.

These stars, the high mass ones among them went unstable in their later years. They collapsed and then exploded, scattering their enriched guts across the galaxy. Guts made of Carbon, Nitrogen, Oxygen and all the fundamental ingredients of life itself. These ingredients become part of gas clouds that condense, collapse, form the next generation of solar systems, stars with orbiting planets, and those planets now have the ingredients for life itself.

So when I look up at the night sky and I know that yes we are a part of this universe, we are in this universe, but perhaps more important than both of those facts is that the universe is in us, when I reflect on that fact, I look up, many people feel small cause they’re small and the universe is big, but I feel big because my atoms came from those stars. There’s a level of connectivity.”

Neil deGrasse Tyson (in a TIME magazine interview)

Essentially, why I study physics.

 

Our current nuclear power plants utilise nuclear fission. The reason for this is due to the fact that fusion is extremely difficult to produce in comparison to fission. Nuclear fission occurs naturally. If you left a block of uranium somewhere, it would literally begin to decay and release energy as heat. However if you leave hydrogen gas alone, it would most definitely not fuse to produce helium.

Stars can make fusion happen relatively easily; they can use their gravitational force to create the high pressures and their already present heat as heat to sustain the fusion. However, the Earth is nowhere near as large or as heavy as a star. To make fusion happen, we utilize multiple methods.

I shall discuss these methods in a future post. I’m sorry i have to cut the post here but i have been delaying this post by a very long time. I hope to release part 2 soon XD.

Regards,

Clyde Lhui 🙂

 

P.s I’m still working on a lot of other posts at the same time, these posts will probably take quite a while to complete. Do tell me if you have any suggestions for new blog posts.

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Home, Science, Science Concepts

Black Holes- Part 1

Hi guys,

New guy here 😀 . I’m Jackson and you would have known me by now after being mentioned in some of the previous posts. However, if you are new to this blog, I am Clyde’s classmate and often discusses Science topics with Clyde. And yes, I am also the new admin here. As I am new here, I will start with an easy topic that requires not much concept          — just fun facts and no Math at all– unlike the mind-boggling Special Relativity that Clyde is doing. Without further ado, let’s jump into one of the most interesting topic, ‘Black Holes’.

Okay, so What is a Black Hole? 

Just from the name itself, most of you would have guessed a hole, a tear in a paper, a pit in the ground. In fact, it is a hole in space time itself, a hole where time slows down so much that you will eventually reach a point where it stops, a hole with an attraction so great that not even light, the fastest thing in the universe can escape. It is an area in the universe where if you drop into…… whoosh, you will disappear, cease to exist, voided from the rest of the world. Sounds dreadful eh? The idea of Black Holes started of as just an abstract concept that was not supported by any evidence and not many scientist believed it exist. Only in 1931, when an astronomer by the name of Chandrasekhar calculated and gave mathematical evidence of potential high mass stars that could form Black Holes, did scientist started paying attention to it.

Even until this day, no scientist has truely understood this mysterious entity, all the laws of physics break down at the singularity of a Black Hole and since no information can escape, there is no way to observe the events at the singularity.

Let’s look at the science of a Black Hole.

Formation of a Black Hole

Imagine an object that is constantly being compressed, its volume will decrease while its mass remains the same, this causes the object’s density to increase as, desity = mass/volume, the mass is a constant hence, a lower volume divided would cause a higher density. An increase in density would also cause the object’s surface gravity increase. As the object is compressed, the object will eventually reach a size where it would have a surface gravity so great that not even light can escape, this is known as the  Schwarzschild Radius. At this point, the object would no longer be able to hold against its own gravity and would collapse infinitely into a point in spacetime known as the singularity, forming a black hole.

However, compressing an object into its Schwarzchild Radius and making a self sustaining Black Hole with brute force is unrealistic and is immensely difficult (so don’t even think about squeezing your golfball into a star hungry galatic black hole of mass destruction to take over the human race). In fact, you will need the power of the stars.

Stars are fueled by nuclear fusion. The proccess of nuclear fusion is basically the combination of two atomic nuclei, releasing the binding energy within the atom. In this proccess, the total mass of the two nucleus decrases, as they are being converted into energy, hence proving the mass energy equivalence. You can find out how much energy is released by finding the change in mass of the atoms and multiplying it with the speed of light squared (3×10^8^2). As the speed of light is HUGE, the energy released, which uses the square of the speed of light, would be unimaginable.
Let’s get back to point, the stars in the universe all start out with one element, Hydrogen. These Hydrogen atoms undergo nuclear fusion and fuses together to form Helium. Helium would then continue fusing to form Carbon, Oxygen and so on. As fusion occurs in a star, energy would be given out as radiation. The radiation would be causing the outward force that prevents the star from collapsing into itself. Usually, an averaged sized star would not have enough energy to continue nuclear fusion after all the carbon has fused to form oxygen, they would cool down into a white dwarf. However, a star that is much more massive would continue the fusion proccess all the way until iron atoms are formed. As iron atoms can no longer fuse, the proccess stops. By then, so much pressure would have built up from the outward force the star is exerting against its own gravity to balance out. Once the fusion proccess stops and the star no longer emits radiation, the gravitational force would suddenly overwhelm the star’s outward force, and in a short period of time, all the matter rushes inwards to the center of the star.

This would be followed by an explosion known as supernova or sometimes even more powerful explosions known as hypernova. After that, the collapse would either stop, forming a neutron star (the densest and smallest stars known to exist in the universe, it is so compressed that all the electron have the energy state to combine with protons to form neutrons, in a proccess known as inverse Beta Decay) or have high enough mass to continue collapsing into a singularity, creating a black hole.

There is another way in which Black Holes can form from the collision of two neutron stars but I will not go into detail on that.

Thanks,
Tiong Jackson :p

Home, Science, Science Concepts

Terminal Velocity

Hi guys,

As I mentioned certain scientific terms in my previous post, i would like to go in depth on those concepts,beginning with terminal velocity, it being the most fundamental concept in my post.

So what is terminal velocity?

Terminal velocity is the velocity of an object when the drag force (dependent on the fluid the object is travelling through) acting upon it is equal to the downward force of gravity acting upon it. Simply put, when the air resistance of a falling object cancels out the gravitational force which is pulling it downwards and accelerating it.

So how do these forces affect the motion of the object? The forces cancelling each other out make the object remain at a constant rate of motion.

You may ask why does the object still move when the forces cancel each other out. This is due to the fact that in the beginning the force of gravity still manages to overcome the drag force, allowing the object to gain speed (accelerate) initially. But as the object increases in velocity, the drag force increases, this effect can also be seen in the case of friction (Drag and friction are pretty much the same thing). Lets assume that a boy is dragging a heavy box, full of files, across a distance of 100 meters, now we will imagine this scenario in two different ways, firstly in the case whereby the boy is walking slowly and in the second whereby the boy is running. So in the first case the boy walks, when he reaches the end, he feels the bottom of the box, where the box and the floor meet, it still feels the same as before, now in the second case, he runs, he once again feels the bottom of the box, this time it feels warmer than before. So what can we infer from this scenario? Before I reveal the answer, i would like to state a few properties of friction:

  1. Friction opposes motion
  2. Friction causes wear and tear
  3. Friction produces heat when kinetic energy is converted into thermal energy

So what can we infer? In the second scenario, there was more heat, therefore we can assume that there was more frictional force produced in the second case.

Now lets go back to what i mentioned previously, air resistance increases (Drag Force) as the object’s velocity increases. As seen in the example above, we can tell that this statement is true.

That’s essentially the definition of terminal velocity. Before we move on, lets do a recap:

  1. Terminal velocity is the velocity an object is at when the gravitational force acting upon it is equal to the drag force acting upon it in the opposite direction therefore cancelling out all forces therefore having a resultant force of 0
  2. The drag force acting upon the object increases as the object accelerates due to the downward force of gravity.

Ok so lets move on to the math behind terminal velocity and some examples of it.

The formula for terminal velocity is as follows: V_t= \sqrt{\frac{2mg}{\rho A C_d }}

Vt=Terminal Velocity

m=Mass of falling object

g= Acceleration of the object due to gravity

ρ= Density of fluid which the object is travelling through

A= Projected area of the object

Cd= Drag Coefficient

I went through everything in my previous post but lets do a recap on these terms:

mass= Amount of matter in an object (SI Unit : kg)

Acceleration = Rate of increase of speed (SI Unit: m/s^2)

Gravitational force= how much gravitational force does an object exert on another object (SI Unit: N/kg)

Density= Mass per unit volume of matter (SI Unit: kg/m^3)

Projected Area= Area of a falling object which is in contact of the air flowing through it. (SI Unit: m^2)- Same as Area

Drag coefficient= A value which depends on the shape of an object and can only be calculated by using the drag force of the object and other factors or by doing actual testing. This value has no units.

That’s all the terms. So now I shall be doing some examples.

So assuming I drop a metal cube which has a mass of 3 kg and has a projected area of 1 m^2 on Earth 90 degrees downward, through air at a temperature of 25 degrees Celsius, what would the Terminal velocity of the cube be?

All we have to do is input all the values into the formula. The acceleration due to gravity on earth is 9.81 m/s^2. The density of air at 25 degrees Celsius is 1.1839 kg/m^3 and the drag coefficient of a cube is 1.05 facing downward. The result is : 6.881101581m/s.

So there’s Terminal Velocity for you!

I would like to thank Mr Tan Ping Hock and Mr Yao Zhi Wei Adrian, My current and previous physics teachers respectively for clearing my doubts about certain concepts within this topic of terminal velocity!

Thanks for reading!

Clyde Lhui

References:

http://en.wikipedia.org/wiki/Drag_coefficient

http://en.wikipedia.org/wiki/Density_of_air

http://en.wikipedia.org/wiki/Terminal_velocity

 

Home, Science, Science investigations

I’m falling down down down down…

Hi everyone!

Recently I have been playing this game called League of Legends (LoL). I’m pretty sure that loads of guys out there play LoL. So I was checking out some info about the game. So in this game, there are 3 maps or Fields of Justice. The first one is Summoner’s Rift, the second being Twisted Treeline and the third is called Howling Abyss. But wait, I’m not here to tell you about LoL. If so why would I label it under ‘Science’? Ok here comes the interesting part. In the description of Howling Abyss LoL said that at screams could be heard in the wind and those were rumoured to be those of warriors who got pushed into the bottomless abyss. So I was thinking “Since its a bottomless pit, the warriors who fell in the abyss wont hit the ground and die so how long will it take for them to die and if they screamed when they died, how long would the screams take to reach the top?”

Ok so the first part’s really simple: How long would they take to die? Assuming there are no flying creatures that eat them up, they did not cry, sweat, pee or breathe through their mouth and they were regular humans, they would take 3 days to die of dehydration.

So that’s part 1 answered, now for part 2. Here’s where it starts to get difficult. How long would their final scream take to reach the top? firstly we have to find out how far down they would have travelled. So assuming they were falling like a skydiver (horizontally) we can find the projected area or the area which is in contact of the air below them. The average male Body Surface Area ( BSA )is 1.9 m^2 therefore to calculate the projected area, we can take the BSA divided by 2 as only one side of their bodies are in contact with the air. therefore the projected area would be 0.95 m^2. Next we have to find their mass. Assuming they were very fit and they had the most ideal body weight according to the Body Mass Index (BMI) and they were average American males in the United States of America who have an average height of 1.763 m, they would have a mass of around 150 pounds or 68.0389 kg. Now we have all the data we need to calculate the terminal velocity of the warriors or the speed they will be at when they stop accelerating. The formula for terminal velocity is as follows: V_t= \sqrt{\frac{2mg}{\rho A C_d }}

Vt= Terminal velocity

m=Mass of falling object

g= Acceleration due to gravity

p(rho)= Density of fluid which the object is travelling through (in this case, air)

A= Projected area

Cd= Drag coefficient

So what do all these mean? well we have been through practically everything except for the drag coefficient. So what is drag coefficient? Drag coefficient is a value which cannot be calculated. It is the value which puts the force generated by drag into account. The drag coefficient of a man is 1.0-1.3. Lets assume that our warriors have a drag coefficient of 1.2, not too skinny yet not too fat. The acceleration due to gravity on Earth is 9.8m/s^2 and the density of air at room temperature (25 degrees Celsius) is 1.1839 kg/m^3 so with everything in SI units we can calculate the terminal velocity of the warriors. The final answer is 54.44492062 m/s assuming all our calculations are right and in SI units. this can be rounded off to 54.4m/s (3 s.f.). The next part that we have to solve is the acceleration period. so from 0m/s to 54.4 m/s how long would it take? Once again assuming that the acceleration due to gravity is around 9.8 m/s^2 as on earth, all we have to do is divide 9.8m/s^2 from 54.4 m/s. The result we arrive at is 5.551020408 s. to find the distance travelled during this time, all we have to do is imagine that all this data is being plotted on a distance time graph and find the area during the acceleration period.

1/2*5.551020408 s*54.4 m/s =150.9877551 m

This can once again be rounded off to 151 m ( 3 s.f.)

Now lets move on to the part where we deal with the duration of the freefall. Assuming that they took EXACTLY 3 days to die of dehydration, they would take 24 h*3= 72 h to die. Now we minus the 5.551020408 s from the 72 h. 72 h = 72 h*60 min = 4320 min =4320 min* 60 s= 259200 s

259200 s – 5.551020408 s = 259194.449 s (my calculator only has this many decimals)

Therefore we can assume that our warriors remained at terminal velocity for 259194.449 s.

So to find the distance they travelled at terminal velocity, all we have to do is:

259194.449 s* 54.4m/s= 14100178.02 m

So our warriors travelled a total distance of:

14100178.02 m + 151 m = 14100329.02 m

Finally to calculate the time taken for the sound to reach the top, we have to divide the distance travelled by the speed of sound which is Mach 1 or 346.13 m/s at room temperature (25 degrees Celsius).

14100329.02 m / 346.13 m/s = 40737.09018 s

That is how long the sound would take to reach the place where our warriors fell from. Converting it to hours : 11.3159 h

So there’s the answer!

If you have anything else, like a science question of some sort or you found a mistake in my calculations and want me to rectify it, please post it in the comments section or you could send me a message via the contact me form!

Thanks for reading!

Clyde Lhui 🙂

References:

http://en.wikipedia.org/wiki/Drag_coefficient

http://en.wikipedia.org/wiki/Body_mass_index

http://en.wikipedia.org/wiki/Human_height

http://en.wikipedia.org/wiki/Terminal_velocity

http://en.wikipedia.org/wiki/Body_surface_area

http://www.sengpielaudio.com/calculator-speedsound.htm

http://en.wikipedia.org/wiki/Density_of_air

http://en.wikipedia.org/wiki/Gravity_of_Earth

http://en.wikipedia.org/wiki/International_System_of_Units