Quantum tunnelling or tunneling is the quantum mechanical phenomenon where a subatomic particle passes through a potential barrier that it cannot surmount under the provision of classical mechanics. Quantum tunnelling plays an essential role in several physical phenomena, such as the nuclear fusion that occurs in main sequence stars like the Sun, it has important applications in the tunnel diode, quantum computing, in the scanning tunnelling microscope. The effect was predicted in the early 20th century, its acceptance as a general physical phenomenon came mid-century. Fundamental quantum mechanical concepts are central to this phenomenon, which makes quantum tunnelling one of the novel implications of quantum mechanics. Quantum tunneling is projected to create physical limits to the size of the transistors used in microprocessors, due to electrons being able to tunnel past them if the transistors are too small. Tunnelling is explained in terms of the Heisenberg uncertainty principle that the quantum object can be known as a wave or as a particle in general.
Quantum tunnelling was developed from the study of radioactivity, discovered in 1896 by Henri Becquerel. Radioactivity was examined further by Marie Curie and Pierre Curie, for which they earned the Nobel Prize in Physics in 1903. Ernest Rutherford and Egon Schweidler studied its nature, verified empirically by Friedrich Kohlrausch; the idea of the half-life and the possibility of predicting decay was created from their work. In 1901, Robert Francis Earhart, while investigating the conduction of gases between spaced electrodes using the Michelson interferometer to measure the spacing, discovered an unexpected conduction regime. J. J. Thomson commented. In 1911 and 1914, then-graduate student Franz Rother, employing Earhart's method for controlling and measuring the electrode separation but with a sensitive platform galvanometer, directly measured steady field emission currents. In 1926, using a still newer platform galvanometer of sensitivity 26 pA, measured the field emission currents in a "hard" vacuum between spaced electrodes.
Quantum tunneling was first noticed in 1927 by Friedrich Hund when he was calculating the ground state of the double-well potential and independently in the same year by Leonid Mandelstam and Mikhail Leontovich in their analysis of the implications of the new Schrödinger wave equation for the motion of a particle in a confining potential of a limited spatial extent. Its first application was a mathematical explanation for alpha decay, done in 1928 by George Gamow and independently by Ronald Gurney and Edward Condon; the two researchers solved the Schrödinger equation for a model nuclear potential and derived a relationship between the half-life of the particle and the energy of emission that depended directly on the mathematical probability of tunnelling. After attending a seminar by Gamow, Max Born recognised the generality of tunnelling, he realised that it was not restricted to nuclear physics, but was a general result of quantum mechanics that applies to many different systems. Shortly thereafter, both groups considered the case of particles tunnelling into the nucleus.
The study of semiconductors and the development of transistors and diodes led to the acceptance of electron tunnelling in solids by 1957. The work of Leo Esaki, Ivar Giaever and Brian Josephson predicted the tunnelling of superconducting Cooper pairs, for which they received the Nobel Prize in Physics in 1973. In 2016, the quantum tunneling of water was discovered. Quantum tunnelling falls under the domain of quantum mechanics: the study of what happens at the quantum scale; this process cannot be directly perceived, but much of its understanding is shaped by the microscopic world, which classical mechanics cannot adequately explain. To understand the phenomenon, particles attempting to travel between potential barriers can be compared to a ball trying to roll over a hill. Classical mechanics predicts that particles that do not have enough energy to classically surmount a barrier will not be able to reach the other side. Thus, a ball without sufficient energy to surmount the hill would roll back down.
Or, lacking the energy to penetrate a wall, it would bounce back or in the extreme case, bury itself inside the wall. In quantum mechanics, these particles can, with a small probability, tunnel to the other side, thus crossing the barrier. Here, the "ball" could, in a sense, borrow energy from its surroundings to tunnel through the wall or "roll over the hill", paying it back by making the reflected electrons more energetic than they otherwise would have been; the reason for this difference comes from the treatment of matter in quantum mechanics as having properties of waves and particles. One interpretation of this duality involves the Heisenberg uncertainty principle, which defines a limit on how the position and the momentum of a particle can be known at the same time; this implies that there are no solutions with a probability of zero, though a solution may approach infinity if, for example, the calculation for its position was taken as a probability of 1, the other, i.e. its speed, would have to be infinity.
Hence, the probability of a given particle's existence on the opposite side of an intervening barrier is non-zero, such particles will appear on the'other' side with a relative frequency proportional to this probability. The wave function of a particle summarises everything that can be known about a physical s
In nuclear physics and nuclear chemistry, nuclear fission is a nuclear reaction or a radioactive decay process in which the nucleus of an atom splits into smaller, lighter nuclei. The fission process produces free neutrons and gamma photons, releases a large amount of energy by the energetic standards of radioactive decay. Nuclear fission of heavy elements was discovered on December 17, 1938 by German Otto Hahn and his assistant Fritz Strassmann, explained theoretically in January 1939 by Lise Meitner and her nephew Otto Robert Frisch. Frisch named the process by analogy with biological fission of living cells. For heavy nuclides, it is an exothermic reaction which can release large amounts of energy both as electromagnetic radiation and as kinetic energy of the fragments. In order for fission to produce energy, the total binding energy of the resulting elements must be more negative than that of the starting element. Fission is a form of nuclear transmutation because the resulting fragments are not the same element as the original atom.
The two nuclei produced are most of comparable but different sizes with a mass ratio of products of about 3 to 2, for common fissile isotopes. Most fissions are binary fissions, but three positively charged fragments are produced, in a ternary fission; the smallest of these fragments in ternary processes ranges in size from a proton to an argon nucleus. Apart from fission induced by a neutron and exploited by humans, a natural form of spontaneous radioactive decay is referred to as fission, occurs in high-mass-number isotopes. Spontaneous fission was discovered in 1940 by Flyorov and Kurchatov in Moscow, when they decided to confirm that, without bombardment by neutrons, the fission rate of uranium was indeed negligible, as predicted by Niels Bohr; the unpredictable composition of the products distinguishes fission from purely quantum-tunneling processes such as proton emission, alpha decay, cluster decay, which give the same products each time. Nuclear fission drives the explosion of nuclear weapons.
Both uses are possible because certain substances called nuclear fuels undergo fission when struck by fission neutrons, in turn emit neutrons when they break apart. This makes a self-sustaining nuclear chain reaction possible, releasing energy at a controlled rate in a nuclear reactor or at a rapid, uncontrolled rate in a nuclear weapon; the amount of free energy contained in nuclear fuel is millions of times the amount of free energy contained in a similar mass of chemical fuel such as gasoline, making nuclear fission a dense source of energy. The products of nuclear fission, are on average far more radioactive than the heavy elements which are fissioned as fuel, remain so for significant amounts of time, giving rise to a nuclear waste problem. Concerns over nuclear waste accumulation and over the destructive potential of nuclear weapons are a counterbalance to the peaceful desire to use fission as an energy source. Nuclear fission can occur without neutron bombardment as a type of radioactive decay.
This type of fission is rare except in a few heavy isotopes. In engineered nuclear devices all nuclear fission occurs as a "nuclear reaction" — a bombardment-driven process that results from the collision of two subatomic particles. In nuclear reactions, a subatomic particle causes changes to it. Nuclear reactions are thus driven by the mechanics of bombardment, not by the constant exponential decay and half-life characteristic of spontaneous radioactive processes. Many types of nuclear reactions are known. Nuclear fission differs from other types of nuclear reactions, in that it can be amplified and sometimes controlled via a nuclear chain reaction. In such a reaction, free neutrons released by each fission event can trigger yet more events, which in turn release more neutrons and cause more fission; the chemical element isotopes that can sustain a fission chain reaction are called nuclear fuels, are said to be fissile. The most common nuclear fuels are 239Pu; these fuels break apart into a bimodal range of chemical elements with atomic masses centering near 95 and 135 u.
Most nuclear fuels undergo spontaneous fission only slowly, decaying instead via an alpha-beta decay chain over periods of millennia to eons. In a nuclear reactor or nuclear weapon, the overwhelming majority of fission events are induced by bombardment with another particle, a neutron, itself produced by prior fission events. Nuclear fission in fissile fuels are the result of the nuclear excitation energy produced when a fissile nucleus captures a neutron; this energy, resulting from the neutron capture, is a result of the attractive nuclear force acting between the neutron and nucleus. It is enough to deform the nucleus into a double-lobed "drop", to the point that nuclear fragments exceed the distances at which the nuclear force can hold two groups of charged nucleons together and, when this happens, the two fragments complete their separation and are driven further apart by their mutually repulsive charges, in a process which becomes irreversible with greater and greater distance. A similar process occurs in fissionable iso
Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group on the periodic table, a reactive nonmetal, an oxidizing agent that forms oxides with most elements as well as with other compounds. By mass, oxygen is the third-most abundant element in the universe, after helium. At standard temperature and pressure, two atoms of the element bind to form dioxygen, a colorless and odorless diatomic gas with the formula O2. Diatomic oxygen gas constitutes 20.8% of the Earth's atmosphere. As compounds including oxides, the element makes up half of the Earth's crust. Dioxygen is used in cellular respiration and many major classes of organic molecules in living organisms contain oxygen, such as proteins, nucleic acids and fats, as do the major constituent inorganic compounds of animal shells and bone. Most of the mass of living organisms is oxygen as a component of water, the major constituent of lifeforms. Oxygen is continuously replenished in Earth's atmosphere by photosynthesis, which uses the energy of sunlight to produce oxygen from water and carbon dioxide.
Oxygen is too chemically reactive to remain a free element in air without being continuously replenished by the photosynthetic action of living organisms. Another form of oxygen, ozone absorbs ultraviolet UVB radiation and the high-altitude ozone layer helps protect the biosphere from ultraviolet radiation. However, ozone present at the surface is a byproduct of thus a pollutant. Oxygen was isolated by Michael Sendivogius before 1604, but it is believed that the element was discovered independently by Carl Wilhelm Scheele, in Uppsala, in 1773 or earlier, Joseph Priestley in Wiltshire, in 1774. Priority is given for Priestley because his work was published first. Priestley, called oxygen "dephlogisticated air", did not recognize it as a chemical element; the name oxygen was coined in 1777 by Antoine Lavoisier, who first recognized oxygen as a chemical element and characterized the role it plays in combustion. Common uses of oxygen include production of steel and textiles, brazing and cutting of steels and other metals, rocket propellant, oxygen therapy, life support systems in aircraft, submarines and diving.
One of the first known experiments on the relationship between combustion and air was conducted by the 2nd century BCE Greek writer on mechanics, Philo of Byzantium. In his work Pneumatica, Philo observed that inverting a vessel over a burning candle and surrounding the vessel's neck with water resulted in some water rising into the neck. Philo incorrectly surmised that parts of the air in the vessel were converted into the classical element fire and thus were able to escape through pores in the glass. Many centuries Leonardo da Vinci built on Philo's work by observing that a portion of air is consumed during combustion and respiration. In the late 17th century, Robert Boyle proved. English chemist John Mayow refined this work by showing that fire requires only a part of air that he called spiritus nitroaereus. In one experiment, he found that placing either a mouse or a lit candle in a closed container over water caused the water to rise and replace one-fourteenth of the air's volume before extinguishing the subjects.
From this he surmised that nitroaereus is consumed in both combustion. Mayow observed that antimony increased in weight when heated, inferred that the nitroaereus must have combined with it, he thought that the lungs separate nitroaereus from air and pass it into the blood and that animal heat and muscle movement result from the reaction of nitroaereus with certain substances in the body. Accounts of these and other experiments and ideas were published in 1668 in his work Tractatus duo in the tract "De respiratione". Robert Hooke, Ole Borch, Mikhail Lomonosov, Pierre Bayen all produced oxygen in experiments in the 17th and the 18th century but none of them recognized it as a chemical element; this may have been in part due to the prevalence of the philosophy of combustion and corrosion called the phlogiston theory, the favored explanation of those processes. Established in 1667 by the German alchemist J. J. Becher, modified by the chemist Georg Ernst Stahl by 1731, phlogiston theory stated that all combustible materials were made of two parts.
One part, called phlogiston, was given off when the substance containing it was burned, while the dephlogisticated part was thought to be its true form, or calx. Combustible materials that leave little residue, such as wood or coal, were thought to be made of phlogiston. Air did not play a role in phlogiston theory, nor were any initial quantitative experiments conducted to test the idea. Polish alchemist and physician Michael Sendivogius in his work De Lapide Philosophorum Tractatus duodecim e naturae fonte et manuali experientia depromti described a substance contained in air, referring to it as'cibus vitae', this substance is identical with oxygen. Sendivogius, during his experiments performed between 1598 and 1604, properly recognized that the substance is equivalent to the gaseous byproduct released by the thermal decomposition of potassium nitrate. In Bugaj’s view, the isolation of oxygen and the proper association of the substance to that part of air, required for life, lends sufficient weight to the discovery of oxygen by Sendivogius.
A stellarator is a plasma device that relies on external magnets to confine a plasma. In the future, scientists researching magnetic confinement fusion aim to use stellarator devices as a vessel for nuclear fusion reactions; the name refers to the possibility of harnessing the power source of the stars, including the sun.stellar object. It is one of the earliest fusion power devices, along with the magnetic mirror; the stellarator was invented by Lyman Spitzer of Princeton University in 1951, much of its early development was carried out by his team at what became the Princeton Plasma Physics Laboratory. Lyman's Model A demonstrated that stellarators could confine plasmas. Larger models followed, but these demonstrated poor performance, suffering from a problem known as pump-out that caused them to lose plasma at rates far worse than theoretical predictions. By the early 1960s, any hope of producing a commercial machine faded, attention turned to studying the fundamental theory of high-energy plasmas.
By the mid-1960s, Spitzer was convinced that the stellarator was matching the Bohm diffusion rate, which suggested it would never be a practical fusion device. The release of information on the USSR's tokamak design in 1968 indicated a leap in performance; this led to the Model C stellarator being converted to the Symmetrical Tokamak as a way to confirm or deny these results. ST confirmed them, large-scale work on the stellarator concept ended as the tokamak got most of the attention; the tokamak proved to have similar problems to the stellarators, but for different reasons. Since the 1990s, this has led to renewed interest in the stellarator design. New methods of construction have increased the quality and power of the magnetic fields, improving performance. A number of new devices have been built to test these concepts. Major examples include Wendelstein 7-X in Germany, the Helically Symmetric Experiment in the USA, the Large Helical Device in Japan. In 1934, Mark Oliphant, Paul Harteck and Ernest Rutherford were the first to achieve fusion on Earth, using a particle accelerator to shoot deuterium nuclei into a metal foil containing deuterium, lithium or other elements.
This system allowed them to measure the nuclear cross section of various fusion reactions, determined that the tritium-deuterium reaction occurred at a lower energy than any other fuel, peaking at about 100,000 electronvolts.100 keV corresponds to a temperature of about a billion kelvins. Due to the Maxwell–Boltzmann statistics, a bulk gas at a much lower temperature will still contain some particles at these much higher energies; because the fusion reactions release so much energy a small number of these reactions can release enough energy to keep the gas at the required temperature. In 1944, Enrico Fermi demonstrated that this would occur at a bulk temperature of about 50 million Celsius, still hot but within the range of existing experimental systems; the key problem was confining such a plasma. But because plasmas are electrically conductive, they are subject to electric and magnetic fields which provide a number of solutions. In a magnetic field, the electrons and nuclei of the plasma circle the magnetic lines of force.
One way to provide some confinement would be to place a tube of fuel inside the open core of a solenoid. A solenoid creates magnetic lines running down its center, fuel would be held away from the walls by orbiting these lines of force, but such an arrangement does not confine the plasma along the length of the tube. The obvious solution is to bend the tube around into a torus shape, so that any one line forms a circle, the particles can circle forever. However, this solution does not work. For purely geometric reasons, the magnets ringing the torus are closer together on the inside curve, inside the "donut hole". Fermi noted this would cause the electrons to drift away from the nuclei causing them to separate and cause large voltages to develop; the resulting electric field would cause the plasma ring inside the torus to expand until it hit the walls of the reactor. In the post-war era, a number of researchers began considering different ways to confine a plasma. George Paget Thomson of Imperial College London proposed a system now known as z-pinch, which runs a current through the plasma.
Due to the Lorentz force, this current creates a magnetic field that pulls the plasma in on itself, keeping it away from the walls of the reactor. This eliminates the need for magnets on the outside. Various teams in the UK had built a number of small experimental devices using this technique by the late 1940s. Another person working on controlled fusion reactors was Ronald Richter, a former German scientist who moved to Argentina after the war, his thermotron used a system of electrical arcs and mechanical compression for heating and confinement. He convinced Juan Perón to fund development of an experimental reactor on an isolated island near the Chilean border. Known as the Huemul Project, this was completed in 1951. Richter soon convinced himself fusion had been achieved in spite of other people working on the project disagreeing; the "success" was announced by Perón on 24 March 1951, becoming the topic of newspaper stories around the world. While preparing for a ski trip to Aspen, Lyman Spitzer received a telephone call from his father, who mentioned an article on Huemul in the New York Times.
Looking over the description in the article, Spitzer concluded it could not work. But the idea stuck with him, he began considering systems that would wor
In fusion power research, the Z-pinch known as zeta pinch, is a type of plasma confinement system that uses an electrical current in the plasma to generate a magnetic field that compresses it. These systems were referred to as pinch or Bennett pinch, but the introduction of the θ-pinch concept led to the need for increased clarity; the name refers to the direction of the current in the devices, the Z-axis on a normal three-dimensional graph. Any machine that causes a pinch effect due to current running in that direction is referred to as a Z-pinch system, this encompasses a wide variety of devices used for an wide variety of purposes. Early uses focused on fusion research in donut-shaped tubes with the Z-axis running down the inside the tube, while modern devices are cylindrical and used to generate high-intensity x-ray sources for the study of nuclear weapons and other roles; the Z-pinch is an application of the Lorentz force, in which a current-carrying conductor in a magnetic field experiences a force.
One example of the Lorentz force is that, if two parallel wires are carrying current in the same direction, the wires will be pulled toward each other. In a Z-pinch machine the wires are replaced by a plasma, which can be thought of as many current-carrying wires; when a current is run through the plasma, the particles in plasma are pulled toward each other by the Lorentz force, thus the plasma contracts. The contraction is counteracted by the increasing gas pressure of the plasma; as the plasma is electrically conductive, a magnetic field nearby will induce a current in it. This provides a way to run a current into the plasma without physical contact, important as a plasma can erode mechanical electrodes. In practical devices this was arranged by placing the plasma vessel inside the core of a transformer, arranged so the plasma itself would be the secondary; when current was sent into the primary side of the transformer, the magnetic field induced a current into the plasma. As induction requires a changing magnetic field, the induced current is supposed to run in a single direction in most reactor designs, the current in the transformer has to be increased over time to produce the varying magnetic field.
This places a limit on the product of confinement time and magnetic field, for any given source of power. In Z-pinch machines the current is provided from a large bank of capacitors and triggered by a spark gap, known as a Marx Bank or Marx generator; as the conductivity of plasma is good, about that of copper, the energy stored in the power source is depleted by running through the plasma. Z-pinch devices are inherently pulsed in nature. Pinch devices were among the earliest efforts in fusion power. Research began in the UK in the immediate post-war era, but a lack of interest led to little development until the 1950s; the announcement of the Huemul Project in early 1951 led to fusion efforts around the world, notably in the UK and in the US. Small experiments were built at labs as various practical issues were addressed, but all of these machines demonstrated unexpected instabilities of the plasma that would cause it to hit the walls of the container vessel; the problem became known as the "kink instability".
By 1953 the "stabilized pinch" seemed to solve the problems encountered on earlier devices. Stabilized pinch machines added external magnets that created a toroidal magnetic field inside the chamber; when the device was fired, this field added to the one created by the current in the plasma. The result was that the straight magnetic field was twisted into a helix, which the particles followed as they traveled around the tube driven by the current. A particle near the outside of the tube that wanted to kink outward would travel along these lines until it returned to the inside of the tube, where its outward-directed motion would bring it back into the centre of the plasma. Researchers in the UK started construction of ZETA in 1954. ZETA was by far the largest fusion device of its era. At the time all fusion research was classified, so progress on ZETA was unknown outside the labs working on it; however US researchers realized that they were about to be outpaced. Teams on both sides of the Atlantic rushed to be the first to complete stabilized pinch machines.
ZETA won the race, by the summer of 1957 it was producing bursts of neutrons on every run. Despite the researchers' reservations, their results were released with great fanfare as the first successful step on the path to commercial fusion energy. However, further study soon demonstrated that the measurements were misleading, none of the machines were near fusion levels. Interest in pinch devices faded, although ZETA and its cousin Sceptre served for many years as experimental devices. A concept of Z-pinch fusion propulsion system was developed through collaboration between NASA and private companies; the energy released by the Z-pinch effect accelerates the lithium propellant to a high speed, resulting in a specific impulse value of 19400 s and thrust of 38 kN. A magnetic nozzle is required to convert the released energy into a useful impulse; this propulsion method could reduce interplanetary travel times. For example, a mission to Mars would take about 35 days one-way with a total burn time of 20 days and a burned propellant mass of 350 tonnes.
Although it remained unknown for years, Soviet scientists used the pinch concept to develop the tokamak device. Unlike the stabilized pinch devices in the US and UK, the tokamak used more energy in the stabilizing magnets, much less in the plasma current; this reduced the instabilities due to the large currents in the plasma, led to g
Vacuum is space devoid of matter. The word stems from the Latin adjective vacuus for "vacant" or "void". An approximation to such vacuum is a region with a gaseous pressure much less than atmospheric pressure. Physicists discuss ideal test results that would occur in a perfect vacuum, which they sometimes call "vacuum" or free space, use the term partial vacuum to refer to an actual imperfect vacuum as one might have in a laboratory or in space. In engineering and applied physics on the other hand, vacuum refers to any space in which the pressure is lower than atmospheric pressure; the Latin term in vacuo is used to describe an object, surrounded by a vacuum. The quality of a partial vacuum refers to how it approaches a perfect vacuum. Other things equal, lower gas pressure means higher-quality vacuum. For example, a typical vacuum cleaner produces enough suction to reduce air pressure by around 20%. Much higher-quality vacuums are possible. Ultra-high vacuum chambers, common in chemistry and engineering, operate below one trillionth of atmospheric pressure, can reach around 100 particles/cm3.
Outer space is an higher-quality vacuum, with the equivalent of just a few hydrogen atoms per cubic meter on average in intergalactic space. According to modern understanding if all matter could be removed from a volume, it would still not be "empty" due to vacuum fluctuations, dark energy, transiting gamma rays, cosmic rays and other phenomena in quantum physics. In the study of electromagnetism in the 19th century, vacuum was thought to be filled with a medium called aether. In modern particle physics, the vacuum state is considered the ground state of a field. Vacuum has been a frequent topic of philosophical debate since ancient Greek times, but was not studied empirically until the 17th century. Evangelista Torricelli produced the first laboratory vacuum in 1643, other experimental techniques were developed as a result of his theories of atmospheric pressure. A torricellian vacuum is created by filling a tall glass container closed at one end with mercury, inverting it in a bowl to contain the mercury.
Vacuum became a valuable industrial tool in the 20th century with the introduction of incandescent light bulbs and vacuum tubes, a wide array of vacuum technology has since become available. The recent development of human spaceflight has raised interest in the impact of vacuum on human health, on life forms in general; the word vacuum comes from Latin, meaning'an empty space, void', noun use of neuter of vacuus, meaning "empty", related to vacare, meaning "be empty". Vacuum is one of the few words in the English language that contains two consecutive letters'u'. There has been much dispute over whether such a thing as a vacuum can exist. Ancient Greek philosophers debated the existence of a vacuum, or void, in the context of atomism, which posited void and atom as the fundamental explanatory elements of physics. Following Plato the abstract concept of a featureless void faced considerable skepticism: it could not be apprehended by the senses, it could not, provide additional explanatory power beyond the physical volume with which it was commensurate and, by definition, it was quite nothing at all, which cannot rightly be said to exist.
Aristotle believed that no void could occur because the denser surrounding material continuum would fill any incipient rarity that might give rise to a void. In his Physics, book IV, Aristotle offered numerous arguments against the void: for example, that motion through a medium which offered no impediment could continue ad infinitum, there being no reason that something would come to rest anywhere in particular. Although Lucretius argued for the existence of vacuum in the first century BC and Hero of Alexandria tried unsuccessfully to create an artificial vacuum in the first century AD, it was European scholars such as Roger Bacon, Blasius of Parma and Walter Burley in the 13th and 14th century who focused considerable attention on these issues. Following Stoic physics in this instance, scholars from the 14th century onward departed from the Aristotelian perspective in favor of a supernatural void beyond the confines of the cosmos itself, a conclusion acknowledged by the 17th century, which helped to segregate natural and theological concerns.
Two thousand years after Plato, René Descartes proposed a geometrically based alternative theory of atomism, without the problematic nothing–everything dichotomy of void and atom. Although Descartes agreed with the contemporary position, that a vacuum does not occur in nature, the success of his namesake coordinate system and more implicitly, the spatial–corporeal component of his metaphysics would come to define the philosophically modern notion of empty space as a quantified extension of volume. By the ancient definition however, directional information and magnitude were conceptually distinct. In the medieval Middle Eastern world, the physicist and Islamic scholar, Al-Farabi, conducted a small experiment concerning the existence of vacuum, in which he investigated handheld plungers in water, he concluded that air's volume can expand to fill available space, he suggested that the concept of perfect vacuum was incoherent. However, according to Nader El-Bizri, the physicist Ibn al-Haytham and the Mu'tazili theologians disagreed with Aristotle and Al-Farabi, they supported the existence of a void.
Using geometry, Ibn al-Haytham mathematically demonstrated that place is the imagined three-dimensional void between the inner surfaces of a containing body. According to Ahmad Dallal, Abū Rayhān al-Bīrūnī states that "there is no observable
In physics, the kinetic energy of an object is the energy that it possesses due to its motion. It is defined as the work needed to accelerate a body of a given mass from rest to its stated velocity. Having gained this energy during its acceleration, the body maintains this kinetic energy unless its speed changes; the same amount of work is done by the body when decelerating from its current speed to a state of rest. In classical mechanics, the kinetic energy of a non-rotating object of mass m traveling at a speed v is 1 2 m v 2. In relativistic mechanics, this is a good approximation only when v is much less than the speed of light; the standard unit of kinetic energy is the joule. The imperial unit of kinetic energy is the foot-pound; the adjective kinetic has its roots in the Greek word κίνησις kinesis, meaning "motion". The dichotomy between kinetic energy and potential energy can be traced back to Aristotle's concepts of actuality and potentiality; the principle in classical mechanics that E ∝ mv2 was first developed by Gottfried Leibniz and Johann Bernoulli, who described kinetic energy as the living force, vis viva.
Willem's Gravesande of the Netherlands provided experimental evidence of this relationship. By dropping weights from different heights into a block of clay, Willem's Gravesande determined that their penetration depth was proportional to the square of their impact speed. Émilie du Châtelet published an explanation. The terms kinetic energy and work in their present scientific meanings date back to the mid-19th century. Early understandings of these ideas can be attributed to Gaspard-Gustave Coriolis, who in 1829 published the paper titled Du Calcul de l'Effet des Machines outlining the mathematics of kinetic energy. William Thomson Lord Kelvin, is given the credit for coining the term "kinetic energy" c. 1849–51. Energy occurs in many forms, including chemical energy, thermal energy, electromagnetic radiation, gravitational energy, electric energy, elastic energy, nuclear energy, rest energy; these can be categorized in two main classes: kinetic energy. Kinetic energy is the movement energy of an object.
Kinetic energy can be transformed into other kinds of energy. Kinetic energy may be best understood by examples that demonstrate how it is transformed to and from other forms of energy. For example, a cyclist uses chemical energy provided by food to accelerate a bicycle to a chosen speed. On a level surface, this speed can be maintained without further work, except to overcome air resistance and friction; the chemical energy has been converted into kinetic energy, the energy of motion, but the process is not efficient and produces heat within the cyclist. The kinetic energy in the moving cyclist and the bicycle can be converted to other forms. For example, the cyclist could encounter a hill just high enough to coast up, so that the bicycle comes to a complete halt at the top; the kinetic energy has now been converted to gravitational potential energy that can be released by freewheeling down the other side of the hill. Since the bicycle lost some of its energy to friction, it never regains all of its speed without additional pedaling.
The energy is not destroyed. Alternatively, the cyclist could connect a dynamo to one of the wheels and generate some electrical energy on the descent; the bicycle would be traveling slower at the bottom of the hill than without the generator because some of the energy has been diverted into electrical energy. Another possibility would be for the cyclist to apply the brakes, in which case the kinetic energy would be dissipated through friction as heat. Like any physical quantity, a function of velocity, the kinetic energy of an object depends on the relationship between the object and the observer's frame of reference. Thus, the kinetic energy of an object is not invariant. Spacecraft use chemical energy to launch and gain considerable kinetic energy to reach orbital velocity. In an circular orbit, this kinetic energy remains constant because there is no friction in near-earth space. However, it becomes apparent at re-entry. If the orbit is elliptical or hyperbolic throughout the orbit kinetic and potential energy are exchanged.
Without loss or gain, the sum of the kinetic and potential energy remains constant. Kinetic energy can be passed from one object to another. In the game of billiards, the player imposes kinetic energy on the cue ball by striking it with the cue stick. If the cue ball collides with another ball, it slows down and the ball it hit accelerates its speed as the kinetic energy is passed on to it. Collisions in billiards are elastic collisions, in which kinetic energy is preserved. In inelastic collisions, kinetic energy is dissipated in various forms of energy, such as heat, binding energy. Flywheels have been developed as a method of energy storage; this illustrates that kinetic energy is stored in rotational motion. Several mathematical descriptions of kinetic energy exist that describe it in the appropriate physical situation. For objects and processes in common human experience, the formula ½mv² given by Newtonian mechanics is suitable. However, if the speed of the object is comparabl