What is Friction?

Friction: Definition
Friction, in simplest terms is a resistance to the relative motion of two objects. It is an inherent force that resists the motion of an object that is in contact with other object. If you try to move a heavy book kept on a table, you will have to apply some force to move the book. Why do you need some force to move the book? This is because the frictional force between the contact area of book and table, is resisting the motion of the book. Have you ever tried ice skating? You must be wondering that there is no friction when you're ice skating and that is why, it's easier to slide so easily on the ice. It is not that there is zero friction between the ice and skates. Zero friction is an ideal concept, one that we use in solving theoretical problems. In the practical world, some friction always exists between two objects coming in contact with each other. Hence, in the case of ice skating, there is friction, but it is very less, making it easier for skaters to perform ice skating. If practically friction becomes zero, it would be impossible for skaters to stop, or for you to sit on a chair, or run on the road. You will keep running indefinitely, in absence of friction!

Is Friction a Force?
Did you notice that we referred to friction as a force while defining it? You must understand that friction is a force that is resistive in nature. It obstructs the motion of another object by applying some force. Are you not wondering from where are frictional forces generated? Let us understand friction, from a molecular level. Ordinary friction that we observe in daily life can be thought of to be a result of roughness in surface. This was what scientists believed for a long time as the main cause of friction. However, today studies have suggested molecular adhesion and plowing effect to be the major causes of friction.

Molecular adhesion is defined as the force that exists between two surfaces coming in contact by the virtue of molecular or electromagnetic attractions between the molecules. To overcome resistance, it becomes essential to break the molecular attraction bond or the adhesive bond. Plowing effect is the frictional force that occurs due to the deformation in size of the object near the point of contact. For example, if a hard object slides on a soft platform, it is the deformation in shape of the surface of soft object that generates friction.

What Friction is Measured In
Friction being a force, the SI unit of measurement of friction is Newton. The value of frictional force that acts between objects in relative motion depends on two major quantities, that is, coefficient of friction µ and net normal reaction N. The frictional force equation is given by, F = μN,

where, μ = coefficient friction, and N = net normal reaction

Understanding the coefficient of friction or μ is very important to calculate understand this concept completely. Coefficient of friction is a scalar quantity that represents the resistance that a surface exerts on substances moving over it. Mathematically, it is the ratio between the frictional force between the surfaces and the force that is applied on the bodies. The coefficient of static friction is a term that is referred for static objects while the term coefficient of kinetic friction is a measure of friction for objects in motion.

BUZZLE

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Basics of Quantum Mechanics for Dummies

 

According to Niels Bohr, the father of the orthodox 'Copenhagen Interpretation' of quantum physics, "Anyone who is not shocked by quantum theory has not understood it". Richard Feynman, one of the founders of quantum field theory remarked, "I think I can safely say that nobody understands quantum theory".
Quantum mechanics deals with the study of particles at the atomic and subatomic levels. The term was coined by Max Born in 1924. Though the theory works to provide accurate predictions of phenomena at the subatomic scales, there is no real understanding of why it works, what it really means or what implications it has for our world picture. Ergo, the best we can do is present you with the central mystery at the heart of quantum mechanics and show you the way its theoretical structure works to provide real world predictions. Once you decide to go down the rabbit hole, the wonderland of quantum physics, will keep you enthralled forever. So here we go.

Introduction to Quantum Mechanics

As seen by a layman, quantum mechanics appears to be more like a bizarre phenomenon or science fantasy flick, full of jargon and complicated mathematical equations. However, it is easier to take a look at the basics of quantum mechanics, provided one isn't baffled by the fact that every electron is a particle, as well as a wave at the same time. In fact, the truth is even stranger. Electron cannot fall on either side of the particle/wave dichotomy. It is only described by a wavefunction or state vector, that can compute the probability or likelihood of finding a particle. The theory sets fundamental limitations on how accurately we can measure particle parameters, replacing classical determinism with probabilistic determinism. The theory describes just about every phenomena in nature, ranging from the blueness of the sky to the structure of the molecules that make organic life possible.

The Failure of Classical Physics

Quantum mechanics arose as a superior theory, due to the fundamental failure of classical mechanics to describe several atomic phenomena. With the discovery of electron, by J.J. Thomson, in the year 1897, the whole idea of classical physics was shown to be inapplicable at the atomic level. Classical physics, which was governed by Newton's laws of motion and Maxwell's laws of electromagnetism, was used to define and predict the motion of particles. But this theory was not able to explain the following three critical and world famous experiments.

Black Body Radiation

According to the classical theory, a black body (any object capable of absorbing radiation at all frequencies and radiating it back) would emit infinite amount of energy. This was not found to be true experimentally. The energy emitted by a black body seemed to be a function of its frequency, showing a typical bell shaped curve. In 1901, Max Planck came up with an equation that accurately described the energy output of a black body, by introducing the Planck's constant (h = 6.626068 x 10^-34 m² kg/s). The Planck relation (E = hν where E is energy, h is the Planck's constant and ν is the frequency of radiation), implied that energy could only be traded in 'packets' or 'quanta'. This discretization brought in by energy quanta was a fundamental shift in thinking, inconsistent with classical institution of physicists at the time. That's why the theory came to be known as quantum physics.

The Photoelectric Effect

When ultraviolet light is shone on certain metal surfaces, electrons are emitted. This phenomenon, whereby electrons in atoms get liberated by the absorption of energy from incident light, is called the photoelectric effect. Classical electromagnetic theory predicted that the number of electrons emitted and their kinetic energy is dependent on the intensity of light reflected from the surface. However, experiments showed that the energy and number of electrons was a function of frequency. Using Planck's energy quantization rule (E = hν ), Albert Einstein conceptualized light as a stream of photons, successfully explaining the photoelectric effect in terms of light frequency. Thus light, which was hitherto known to be a wave, was now known to have a dual character - that of a wave and a particle.

Optical Line Spectra

Classical electromagnetic theory could not explain the optical line emission or absorption spectra, arising from gases and liquids. Bohr's atomic model, based on angular momentum quantization and quantized energy levels provided accurate experimental values of optical spectra for Hydrogen, thus providing further validation to the quantization approach.

All these phenomenological developments and heuristic theory laid ground for the old quantum theory. It was further amended by scientists like W. Heisenberg and E. Schrödinger to form the new quantum theory based on the central principle of the wave nature of matter particles.

Basics of Quantum Physics For Dummies

To understand the quantum realm, you need to unlearn and unplug yourself from classical intuition - which serves us well in the macroscopic world, but is eminently useless in here. Let us peel off our classical intuition layer by layer.

De Broglie's Matter Waves

Experiments like the photoelectric effect demonstrated particle wave duality of light. If light waves behaved like particles, could matter particles also behave like waves? This was the question posed by Louis de Broglie, a French physicist and answered through his PhD thesis in 1924. He hypothesized the existence of Matter Waves corresponding to every particle, whose wavelength would be inversely proportional to the momentum of the particle.

λ_matter = h / p

(where h is the Planck's constant and p is the momentum)

Experiments conducted by Davisson and Germer at Bell Labs in 1927, conclusively proved the wave nature of particles. The duo fired electrons at a crystallized nickel target to observe wave-like diffraction patterns. Till date, such a pattern was only observed for light waves. Thus it was conclusively proved that particles behave like waves and vice versa.

In 1926, Erwin Schrödinger formulated an equation that described the behavior of these matter waves. He successfully derived the energy spectrum of Hydrogen atom, by treating orbital electrons as standing matter waves. Max Born interpreted the square of amplitude of these waves to be the probability of finding associated particles in a localized region. All these developments led to the establishment of quantum mechanics as a scientific theory, well grounded in experiment and formalism. The wavefunction describing any particle in quantum mechanics is a matter wave, whose form is computed through the use of Schrödinger equation. Ergo, matter waves form the central most important feature of quantum mechanics.

Heisenberg's Uncertainty Principle

The more precisely the position is determined, the less precisely the momentum is known in this instant, and vice versa. - Werner Heisenberg

A direct consequence of the dual (particle/wave) nature of all matter and energy is the uncertainty principle. In its most non-nerdy version, it states - 'You cannot know the position of a particle and how fast it's moving with arbitrary precision at the same moment.' Or, 'It is fundamentally impossible to simultaneously know the position and momentum of a particle at the same moment with arbitrary accuracy.' Quantitatively, the principle can be stated as follows:

Δx.Δp ≥ h/2π

(where Δx is the uncertainty in position, Δp is the uncertainty in momentum and h is Planck's constant)

The fundamental limitation on accuracy is quantified in the form of the Planck's constant. No matter how accurate your measuring equipment is, it is singularly impossible to reduce the error in measurement to less than the Planck's constant. This is because a particle being a matter wave, is inherently delocalized (spread out in space). The more accurately you know the position, more uncertain you are about the momentum and vice versa. Generally, the uncertainty principle is applicable to any dual set of complementary physical quantities that cannot be measured with arbitrary precision.

The Wavefunction (Ψ) Encodes All Particle Information

Since we cannot measure the position of a particle accurately, the entire concept of a fixed orbit or trajectory goes for a toss. You can no longer plot the path of a particle on a graph, like in Newtonian mechanics. The particle itself being a wave has its position spread out in space. The entirety of information about particles is encoded in the wavefunction Ψ, that is computed in quantum mechanics, using the Schrodinger equation - a partial differential equation that can determine the nature and time development of the wavefunction.

Determinism is Probabilistic

Once we have Ψ (the wave function) - for a system, the probability of a particle's position is determined by the square of its modulus - │Ψ│². So we have essentially given up on predicting the position of a particle accurately, because of the uncertainty principle. All we can do is predict the probabilities. One unnerving consequence of this fact is that, until a measurement is made, the particle essentially exists in all positions! This paradox was put forward famously in the form of the Schrödinger's cat in the box thought experiment.

Schrödinger's Cat in a Box

This is a hypothetical experiment in which a cat's put inside a box, with some equipment which releases poisonous gas, on detection of beta particles emitted by a radioactive source. Since beta emission is random by nature, there is no way of knowing when the cat dies.

There is no way of knowing whether the cat is dead or alive, until the box is opened. So until we look inside, according to quantum theory, the cat is both dead and alive! This is the fundamental paradox presented by the theory. It's one way of illustrating the way quantum mechanics forces us to think. Until the position of a particle is measured, it exists in all positions at the same time, just like the cat is both dead and alive.

What we have introduced you to here, is just the proverbial tip of the iceberg. Quantum mechanics allows one to think of interactions between correlated objects, at a pace faster than the speed of light (the phenomenon known as quantum entanglement), frictionless fluid flow in the form of superfluids with zero viscosity and current flow with zero resistance in superconductors. It may one day revolutionize the way computers operate, through quantum computing. It also lays the foundation of advanced theory of relativity, knows as quantum field theory, which underlies all of particle physics.

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Seberapa Jauhkah 1 Tahun Cahaya Itu?

Tahun cahaya (bahasa Inggris:light year) adalah satuan panjang yang didefinisikan sebagai jarak yang ditempuh cahaya dalam satu tahun melewati ruang hampa udara. Istilah tahun yang digunakan untuk perhitungan adalah tahun Julian yang mempunyai 365,25 hari atau 31.557.600 detik. Kadang kala rata-rata tahun tropis 31.556.925,9747 detik digunakan. Karena cahaya menempuh kecepatan 299.792.458 meter per detik (m/s) dalam ruang hampa udara, maka dengan menggunakan tahun Julian, satu tahun cahaya sama dengan 9.460.730.472.580,8 kilometer (5.878.625.373.184 mil).

Cahaya dalam 1 detik menempuh jarak 300.000.000 meter

Sekarang coba di hitung :

1 tahun = 365 hari

1 hari = 24 jam

1 jam = 60 menit

1 menit = 60 detik

Maka, 1 tahun = 31536000 detik

Jarak 1 tahun cahaya = 31536000 detik x 300.000.000 meter/detik = 9,4608 × 1015 meter

Satuan SI dari besaran panjang adalah meter. Selain satuan SI ini, besaran panjang juga memiliki banyak satuan yang lain seperti inci, kaki, yard, mil, dan tahun cahaya. Satu inci kira-kira sama dengan jari-jari bola ping-pong. Satu kaki kira-kira sama dengan jarak satu langkah. Satu mil kira-kira sama dengan empat kali keliling lapangan sepak bola.

Lalu sepanjang apakah jarak 1 tahun cahaya itu ?

Untuk dapat membayangkan jarak 1 tahun cahaya, pejamkanlah matamu sejenak . Bayangkanlah kamu berada dalam pesawat yang kecepatannya sama dengan kecepatan cahaya yakni 300.000 km per sekon.

Ini berarti dalam satu kedipan mata, kamu yang sebelummnya berada di Banda Aceh akan sampai di Papua. Dalam satu menit kamu telah mengelilingi bumi sebanyak tujuh kali. Dan dalam waktu lima menit kamu telah tiba di matahari. Sekarang bayangkanlah benar-benar, seolah-olah kamu sedang berada di dalam pesawat ruang angkasa. Hari berganti hari,bulan bergani bulan, sampai genap satahun kamu berkendaraan. Alangkah jauhnya jarak yang telah kamu tempuh. Itulah jarak satu tahun cahaya.

Sekarang marilah kita gunakan satuan tahun cahaya ini untuk membayangkan besar dari jagad raya.Jagad raya ini berisikan bintang-bintang yang berkelompok dalam gugusan yang disebut galaksi.

Setiap galaksi beranggotakan bintang-bintang dalam jumlah yang amat banyak, dari ratusan ribu hingga miliaran bintang. Garis tengah suatu galaksi bervariasi dari sekitar 10.000 tahun cahaya hingga lebih dari 100.000 tahun cahaya, sedangkan jarak antara dua galaksi yang berdekatan bias mencapai jutaan tahun cahaya. Padahal di jagad raya ini diperkirakan terdapat ratusan miliar galaksi. Dapat kamu bayangkan, betapa luasnya jagad raya ini! Lalu , bagaimanakah posisi planet bumi di dalam jagad raya ini? Bagaimana pula dengan kita, manusia-manusia yang hidup diatasnya?

Keberadaan bumi di jagad raya ini bagaikan sebutir pasir yang melayang di tengah gurun pasir yang maha luas.

Adakah Sang Pencipta, yang telah menciptakan jagad raya yang maha luas ini, betapa kecilnya arti keberadaan kita kita agar kita sadar bahwa sungguh tak pantas bagi kita untuk berlaku sombong di muka bumi. Agar kita sadar bahwa sudah sepantasnyalah kita merendahkan diri di hadapan-Nya.

sumber : vivanews.com

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Sejarah Terbentuknya Reaksi Nuklir

Pada tahun 1896, Antoine Henri Becquerel menemukan radioaktivitas uranium.

Pada tahun 1902, Marie dan Pierre Curie mengisolasi logam radioaktif disebut radium

Pada tahun 1905, Albert Einstein merumuskan dalam teori Teori Relativitas Khusus.

Menurut teori ini, massa dapat dianggap sebagai bentuk lain dari energi. Menurut Einstein, jika entah bagaimana kita bisa mengubah massa menjadi energi, akan mungkin untuk “membebaskan” sejumlah besar energi.

Selama dekade berikutnya, langkah besar diambil oleh Ernest Rutherford dan Niels Bohr menjelaskan struktur atom yang lebih tepat. Mereka mengatakan, dari inti bermuatan positif, dan elektron bermuatan negatif yang berputar di sekitar inti. Itu adalah inti, para ilmuwan menyimpulkan, bahwa harus dipecah atau “meledak” jika energi atom akan dirilis.

 

Pada tahun 1934, Enrico Fermi Italia menghancurkan atom berat dengan menyemprotkannya pada neutron. Namun dia tidak menyadari bahwa ia telah memperoleh fisi nuklir.

Pada Desember 1938, meskipun, Otto Hahn dan Fritz Strassman di Berlin melakukan eksperimen serupa dengan uranium dan menjadi prestasi dunia. Mereka telah menghasilkan fisi nuklir, mereka telah memisahkan atom yaitu 33 tahun setelah Einstein mengatakan hal itu bisa dilakukan bahwa massa berubah menjadi energi.

Pada tanggal 2 Agustus 1939, Albert Einstein menulis surat kepada Presiden Amerika, Franklin D. Roosevelt. Selama empat bulan terakhir, ia telah membuat kemungkinan melalui karya Joliot di Perancis serta Fermi dan Szilard di Amerika yang memungkinkan mengatur reaksi nuklir dalam sebuah massa besar uranium. ..

Dan ini fenomena baru juga yang akan mengarah pada pembangunan bom … Sebuah bom tunggal dari jenis ini, dilakukan dengan perahu atau meledak di sebuah port, mungkin sangat baik menghancurkan seluruh pelabuhan bersama-sama dengan beberapa daerah sekitarnya. Dia mendesak Roosevelt untuk memulai program nuklir tanpa keterlambatan.

Dalam 1 tahun kemudian Einstein menyesalkan peran dia bermain dalam pengembangan senjata destruktif seperti itu: “Aku melakukan satu kesalahan besar dalam hidup saya,” katanya kepada Linus Pauling, ilmuwan terkemuka lain, “ketika saya menandatangani surat kepada Presiden Roosevelt merekomendasikan bahwa bom atom dibuat”.

Pada Desember 1942 di University of Chicago, ahli fisika Italia Enrico Fermi berhasil menghasilkan reaksi berantai nuklir pertama. Hal ini dilakukan dengan pengaturan uranium alam gumpalan didistribusikan dalam setumpuk besar grafit murni, suatu bentuk karbonnya. Dalam reaktor nuklir, moderator grafit berfungsi untuk memperlambat neutron.

Pada Agustus 1942, selama Perang Dunia II, Amerika Serikat mendirikan Proyek Manhattan.Tujuan dari proyek ini adalah untuk mengembangkan, membangun, dan menguji bom. Banyak ilmuwan Amerika terkemuka, termasuk fisikawan Enrico Fermi dan J. Robert Oppenheimer dan kimia Harold Urey, yang terkait dengan proyek, yang dipimpin oleh seorang insinyur Angkatan Darat AS, Brigadir Jenderal Leslie R. Groves.

Pada tanggal 31 Mei 1945, enam belas orang bertemu di kantor Menteri Perang Henry L. Stimson. Enam belas orang ini ada di sana untuk membuat keputusan tentang senjata Amerika rata-rata belum pernah mendengar, bom atom. Mereka memilih target masa depan untuk “The Bomb.” Apa yang mereka bicarakan adalah “hubungan baru manusia dengan alam semesta,” seperti dikatakan oleh Stimson. Sekretaris tampaknya mengatakan, berada di titik balik yang paling kritis dalam seluruh sejarah yang dicatat.

Pada tanggal 16 Juli 1945, bom atom pertama atau A-bom, diuji di Alamogordo, New Mexico.

Pada tanggal 6 Agustus 1945, Enola Gay, pesawat Amerika, menjatuhkan bom atom pertama yang pernah digunakan dalam peperangan di Hiroshima, Jepang, akhirnya menewaskan lebih dari 140.000 orang. Pada tanggal 9 Agustus 1945, Amerika Serikat menjatuhkan bom atom kedua, kali ini di kota Jepang Nagasaki. Walaupun meleset satu mil dari sasaran, tapi membunuh 75.000 orang.

Pada tanggal 29 Agustus 1949, Uni Soviet menguji bom atom pertama.

Pada tanggal 1 November, 1952 percobaan, skala penuh berhasil dilakukan oleh Amerika Serikat dengan perangkat fusi-jenis.

Pada tahun 1946, Komisi Energi Atom (AEC), lembaga sipil dari pemerintah Amerika Serikat, mendirikan UU Energi Atom untuk mengelola dan mengatur produksi dan penggunaan tenaga atom. Di antara program-program utama dari komisi baru ini adalah produksi bahan fisik bom; pencegahan kecelakaan; penelitian biologi, kesehatan, metalurgi dan produksi tenaga listrik dari atom, studi dalam produksi pesawat nuklir; dan deklasifikasi data pada energi atom.

sumber : wikipedia

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How does Sound Travel?

Sound is a series of compression and rarefraction waves that can travel long distances. It is produced by the vibration of the particles present in its medium; a medium is the material through which sound can travel. Presence of a medium is a must for the movement of sound waves. There are various types of medium through which sound waves can move like solids, liquids, gases, plasma, etc. Sound cannot travel through vacuum.

Characteristics of Sound Waves

The speed and the physical characteristics of sound largely varies with the change in its ambient conditions. The speed of sound depends on the density of the medium though which it is traveling. If its density is quite high, then sound would travel at a faster pace. When sound travels through gaseous medium, its speed varies with respect to changes in temperature.

The frequency of sound waves is nothing but the total number of vibrations that have been produced. The length of sound waves vary according to its frequency. Sound waves with long wavelengths have low frequency or low pitch; and those with short wavelengths have high frequency or high pitch. Our ears are capable of hearing only those sound waves which lie in the range between 20 and 20,000 vibrations per second.

How do Sound Waves Travel?
Basically, there are three things that are required for the transmission of sound. They are: a source that can transmit the sound, a medium through which sound can pass (like, water, air, etc.), and the receiver or the detector which receives the sound. The traveling process of sound has been explained below.

Creation of Sound
When a physical object moves in air, it causes vibrations which leads to formation of a series of compression waves in the air. These waves travel in the form of sound. For instance, when we strum the strings of a guitar or hit the head of a drum, the to-and-fro motion of the strings or the drum head creates compression waves of sound in the surrounding air. Similarly, when we speak, our vocal cords vibrate and the sound is created. This type of vibration occurs not just in atmospheric air but in other mediums like, solids and liquids as well. For instance, when a train is moving on a railroad made up of steel, the sound waves thus produced travel via these tracks.

At room temperature, sound travels through air with a speed of 343 m/s, through water at 1,482 m/s, and through steel at 5,960 m/s. As you can see, sound waves travel in a gaseous medium at a slow pace because its molecules are loosely bound and have to cover a long distance to collide with another molecule. In solid medium, the atoms are so closely packed that the vibration is readily transmitted to the neighboring atoms, and sound travels quite fast. In liquid medium, the bonding between the component particles are not as strong as in solids. Therefore, the sound waves move through it at a less speed as compared to solid.

 

Detection of Sound
When the sound waves hit the receiver, it causes some vibration in that object. The detector captures just a part of the energy from the moving sound wave. This energy of vibration is then converted to electrical signals. Thus, when the sound waves reach our ears, the eardrum present inside it vibrates. This vibration reaches our inner ear and is converted into nerve signals. As a result, we can hear the sound. Devices like microphone can detect sound. The sound waves create vibrations in its membrane which forms electrical signals that gets amplified and recorded.

So, how does sound travel? Vibration of an object causes vibrations of the same frequency in the surrounding medium. The vibrations are sent to the inner ear. After the auditory nerve picks up these vibrations, electrical signals are sent to the brain where the vibrations are recognized as sound.

buzzle

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Kecerdasan Koloni Semut

Seekor semut adalah mahluk yang bodoh, ukurannya kecil dan tidak mampu melihat jauh. Dilihat dari ukurannya, lansekap dimana ia bergerak ke mana-mana mestilah sangat tidak beraturan baginya. Lalu bagaimana semut dalam koloni semut mampu menemukan makanan dengan cepat dan umumnya lewat rute terpendek, ketimbang fakta kalau tidak satupun memberikan perintah operasi?
Kembali, ini adalah masalah feromon dan kecerdasan gerombolan. Sebuah koloni semut adalah mesin pemproses paralel yang mengesankan. Kevin Kelly mengatakan : “Semut adalah masa lalu organisasi sosial dan masa depan komputer.” Semut berfungsi secara mandiri dan serempak serta berkomunikasi satu sama lain ‘tanpa sadar’ lewat feromon.
Sejumlah semut perintis dilepas untuk mencari makanan, pergi ke berbagai arah secara mandiri dan acak. Mereka terus menerus melepaskan feromon baik saat pergi dari sarang maupun kembali. Dengan cara ini, jejak yang digunakan oleh banyak semut akan memiliki aroma feromon yang kuat. Feromon adalah zat yang menguap sangat lambat sehingga waktu peluruhan jejak semut sangat panjang.

Anggap satu ekor semut secara tidak sengaja menemukan jalan berguna terpendek menuju makanan. Katakanlah jalur A. Lalu ia akan mampu menemui makanan dan kembali dengan jalur yang sama dalam waktu terpendek, dibandingkan dengan semut lain yang tidak menempuh rute ini. Perjalanan pergi dan pulang sepanjang jalur A akan menghasilkan kekuatan feromon dua kali lipat, dibandingkan jalur yang dua kali lebih panjang. Berbagai semut dapat melewati berbagai jalur dan jalur-jalur ini dapat berpotongan. Pada persimpangan dimana banyak jalur berpotongan, semut memilih jalur yang mengeluarkan bau paling kuat, dan karenanya memperkuat bau jalur itu sendiri (hukum kembalian menanjak atau umpan balik positif).
Kemunculan paksa mandiri jalur optimum ini adalah contoh dari AUTOKATALISIS, dan ia hanyalah satu contoh dari berbagai proses pembentukan pola dalam sistem kompleks.

Penyelidikan satu tipe sistem kompleks dapat memberikan petunjuk pada apa yang dapat terjadi dalam sistem kompleks lainnya. Kasus yang paling jelas adalah : Bagaimana memahami kecerdasan manusia sebagai sejenis kecerdasan gerombolan. Kecerdasan manusia muncul dari interaksi antar sel syaraf, padahal kenyataannya tiap sel syaraf itu bodoh sebodoh-bodohnya.

Sumber : 

Diterjemahkan dari
Vinod Kumar Wadhawan. 2009. Complexity Explained.
Referensi lanjut

1. J. Doyne Farmer dan Alletta Bellini. 1991. Artificial Life: The Coming Evolution. Dalam Artificial Life II, SFI Studies in the Sciences of Complexity, vol. X, disunting oleh C.G. Langton, C. Taylor, J.D. Farmer dan S. Resmussen, Addison-Wesley.
2. Kevin Kelly, 1995. Out of Control: The New Biology of Machines, Social Systems, and the Economic World. Basic Books.
3. M. Dorigo and T. Stützle. Ant Colony Optimization. MIT Press, Cambridge, MA, 2004.

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Fakta Menarik Tentang Fisika

Menurut penulis We Need to Talk About Kevin, Marcus Crown, berikut 10 fakta fisika aneh itu:

1. Jika matahari terbuat dari pisang.

Matahari panas karena beratnya yang luar biasa, sekitar bermiliar-miliar ton dan membuatnya menjadi inti tekanan kolosal. Tekanan besar menimbulkan temperatur besar. Jika matahari terbuat dari pisang, maka beratnya akan bermiliar-miliar ton dan memiliki efek yang sama dengan matahari.

2. Semua materi pembuat ras manusia dapat masuk dalam kotak gula.

Atom merupakan 99,9999999999999999% ruang kosong. Jika semua atom dipaksa bersatu dan menghilangkan ruang di antaranya seperti kotak gula, maka massanya sekitar 10 kali massa manusia hidup. Hal ini serupa yang terjadi pada bintang netron, massa super padat peninggalan supernova.

3. Peristiwa di masa depan dapat mempengaruhi peristiwa di masa lalu.

Keanehan dunia kuantum didokumentasikan. Tetapi keanehan itu semakin aneh. Menurut eksperimen fisikawan John Wheeler dan peneliti lain pada 2007, perubahan partikel masa kini dapat mengubah partikel pada masa lalu.

4. Hampir sebagian besar semesta menghilang

Kemungkinan terdapat lebih dari 100 miliar galaksi di kosmos. Setiap galaksi memiliki 10 juta bintang. Matahari kita memiliki berat bermiliar-miliar ton. Materi ini merupakan materi terlihat di semesta.

Materi lain disebut ‘materi gelap’. Materi ini masih butuh penjelasan dan tampaknya materi ini merupakan perluasan semesta.

5. Benda dapat bergerak lebih cepat dari cahaya.

Kecepatan cahaya konstan pada ruang hampa adalah 300 ribu km/detik, dan cahaya tak selalu melewati ruang hampa. Dalam air, foton bergerak sepertiga kecepatan awal. Dalam reaktor nuklir, beberapa partikel dipaksa bergerak dalam kecepatan tinggi bahkan lebih cepat dari cahaya.

6. Ada jumlah tak terbatas saat menulis dan membaca

Menurut standar model kosmologi saat ini, jumlah semesta yang dapat dihitung pun tak ada batasnya seperti buih. Namun, jumlah kemungkinan sejarah terbatas karena jumlah peristiwa terjadi juga terbatas.

7. Lubang Hitam tidak hitam

Lubang hitam memang sangat gelap, tapi tak hitam. Mereka bersinar dan memberi sedikit spektrum cahaya, temasuk cahaya yang dapat dilihat.

8. Penjelasan mendasar dari semesta tak termasuk masa lalu, kini atau masa depan

Menurut teori relativitas, tak ada hal seperti masa kini atau masa depan atau masa lalu. Bingkai waktu sangat relatif. Waktu kita sama karena kita bergerak pada kecepatan yang sama. Jika kita bergerak pada kecepatan berbeda, kita akan menemukan bahwa kita menua lebih cepat.

9. Partikel dapat mempengaruhi sisi lain semesta dalam sekejab

Ketika elektron bertemu kembaran antimateri, keduanya akan hancur dalam kilatan energi dan dua foton akan terbang dari ledakan itu.

Kembaran itu akan mulai berputar pada arah sebaliknya, dan secara instan kembaran di sisi lain semesta juga ikut berputar.

10. Semakin cepat bergerak, semakin berat

Jika Anda berlari dengan cepat, berat Anda akan bertambah. Tak permanen, tapi secara sesaat akan menambah sedikit berat. Menurut teori relativitas, massa dan energi adalah sama. Semakin banyak energi yang dikeluarkan, semakin berat massanya

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Law of Inertia

After I was first introduced to the law of inertia, I was relieved to know that my 'Laziness' made sense after all. It's not just me who doesn't feel like changing things about myself, but it's in the very nature of matter itself, to resist any kind of change! The law associated with inertia is the central axiom on which the whole edifice of Newtonian mechanics is based.

 

Definition

The word 'inertia' is derived from the Latin word 'iners', which means 'idle'. Here is the definition of inertia, as stated by Sir Isaac Newton in his book, fondly referred to as Principia,

"The vis insita, or innate force of matter, is a power of resisting by which every body, as much as in it lies, endeavors to preserve its present state, whether it be of rest or of moving uniformly forward in a straight line."

To simplify the definition, what Newton refers to as inertia is the property of matter, which resists all kinds of change and makes it stay in its state of rest or uniform motion in a straight line. This idea of inertia, was then used to define Newton's first law of motion which states:

"Every body prefers to stay in a state of rest or keeps moving at a constant velocity, unless an external unbalanced force acts upon it."

The law makes a connection between inertia and the concept of force. Rather, it states what happens in the absence of a force. The inertia of a body is its inherent tendency to resist changes of any kind. Left to itself, a particle will continue to be at rest or move at a constant velocity, in an environment devoid of any unbalanced forces.

The mass of a body is the measure of its inertia. More the mass of any body, more is its inertia and more is its resistance to change its state. On Earth, being in the grip of our planet's gravitational force, electromagnetic forces and in the presence of frictional forces, we cannot see the effects of inertia.

Examples

The only way you can truly see the effects of inertia in full measure, is in the absence of forces, which is only in outer space. Still you can see its effects, though they are masked by gravitational and frictional forces. When an object is thrown from a flying plane, it continues to move with the same velocity as the plane, for some time, till it hits the ground, under the effect of gravity. This linear velocity that it gets from its inertia of staying on the plane makes it fall in a trajectory that is not a straight fall, but a curved one.

In outer space, where there is little or no effect of gravity, a ball thrown away or a bullet fired will continue moving in a straight line forever until it comes in contact with a gravitational or electromagnetic force which halts or changes its direction.

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Ohm's Law

Ohm's Law, a principle discovered in 1827 and named after the German scientist, Georg Simon Ohm, is a basic law of electricity. This law defines the mathematical relationship between three fundamental electrical factors; voltage, resistance and electric current. Ohm's law can be applied to electrical circuits and is valid for both direct as well as alternating current.

What exactly is Ohm's Law?

Consider an electric circuit through which an electric current (I) is passed. According to Ohm's Law, the current flowing through the circuit is directly proportional to the potential difference (V) between two points in the circuit and is inversely proportional to the resistance (R) between them.

Experimentally, it is observed that when the voltage between the points is doubled, then the current is also doubled, and if the resistance is doubled, then the current halves, which indicates that the current flowing is directly proportional to the potential difference and is inversely proportional to the resistance.

Parameters involved in Ohm's Law

The different parameters involved in Ohm's Law are voltage, current, resistance and power.

Voltage (V/E) is the potential difference between two points in a circuit and is measured in volts (V).
Current (I) is the flow of electric charge from negative to positive on the conductor surface and is measured in amperes (A) or amps.
Resistance (R) is the measure of opposition caused to the flow of electric charge. Resistance determines how much current will actually flow through the conductor and is used to control the levels of current and voltage. Resistance is measured in ohms (Ω).

Ohm's Law's Mathematical Equation

Ohm's Law's Mathematical Equation is the simplest and most important equation that can be used while designing or analyzing circuits. According to Ohm's Law;

Current (I) = Voltage (V) / Resistance (R)

Using this simple mathematical equation, one could use the two known parameters to find the third unknown parameter. For example, if the current flowing and voltage is known, then the resistance can be easily found by reorganizing the above equation.

Resistance (R) = Voltage (V) / Current (I)

If the current and resistance is known, then again by rearranging the formula, the voltage between the two points can be determined.

Voltage (V) = Current (I) × Resistance (R)

The above equations can be used to calculate the current through resistors, voltage drops across resistors, output power and power ratings of resistors.

Another useful equation is that of the power equation, where the power is equal to the voltage multiplied by the current. P = V × I

In case the voltage details are unknown, and only the current and resistance figures are available, we can reorganize the equation and calculate the power directly;

Since V = IR, by substituting this in the above power equation P = VI, we get P = I × R × I

Some of the other equations that can be derived from the standard equation and the power equation are as follows;

E = IR (Since E, electromotive force = potential difference, V)
R = E/I
I = E/R
P = EI
E = P/I
I = P/E.
P = I2R
R = P/I2
I = sqrt (P/R)
P = E2/R
R = E2/P
E = sqrt (PR)

In Ohm's Law, the voltage and resistance are not affected by changes in the other parameters. Only the current parameter changes according to respective changes in the voltage and resistance. Ohm's Law is extremely useful in the engineering (electrical/ electronic) field, because of the way it relates the three electrical quantities; current, voltage and resistance. It shows how these three are interdependent on a macroscopic level. These equations are used a lot in cases of car audios to find out the current moving through the circuit.

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