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Portal:Physics
The Physics Portal
Physics is the scientific study of matter, its fundamental constituents, its motion and behavior through space and time, and the related entities of energy and force. Physics is one of the most fundamental scientific disciplines. A scientist who specializes in the field of physics is called a physicist.
Physics is one of the oldest academic disciplines. Over much of the past two millennia, physics, chemistry, biology, and certain branches of mathematics were a part of natural philosophy, but during the Scientific Revolution in the 17th century, these natural sciences branched into separate research endeavors. Physics intersects with many interdisciplinary areas of research, such as biophysics and quantum chemistry, and the boundaries of physics are not rigidly defined. New ideas in physics often explain the fundamental mechanisms studied by other sciences and suggest new avenues of research in these and other academic disciplines such as mathematics and philosophy.
Advances in physics often enable new technologies. For example, advances in the understanding of electromagnetism, solid-state physics, and nuclear physics led directly to the development of technologies that have transformed modern society, such as television, computers, domestic appliances, and nuclear weapons; advances in thermodynamics led to the development of industrialization; and advances in mechanics inspired the development of calculus. (Full article...)
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The speed of light in vacuum, commonly denoted c, is a universal physical constant that is exactly equal to 299,792,458 metres per second (approximately 300,000 kilometres per second; 186,000 miles per second; 671 million miles per hour). It is exact because, by a 1983 international agreement, a metre is defined as the length of the path travelled by light in vacuum during a time interval of 1⁄299792458 second. According to the special theory of relativity, c is the upper limit for the speed at which conventional matter or energy (and thus any signal carrying information) can travel through space.
All forms of electromagnetic radiation, including visible light, travel at the speed of light. For many practical purposes, light and other electromagnetic waves will appear to propagate instantaneously, but for long distances and very sensitive measurements, their finite speed has noticeable effects. Much starlight viewed on Earth is from the distant past, allowing humans to study the history of the universe by viewing distant objects. When communicating with distant space probes, it can take minutes to hours for signals to travel. In computing, the speed of light fixes the ultimate minimum communication delay. The speed of light can be used in time of flight measurements to measure large distances to extremely high precision. (Full article...)
Did you know -
- ... the mirage of astronomical objects is an optical phenomenon, which produces distorted or multiple images of astronomical objects such as the Sun, the Moon, the planets, bright stars and very bright comets
- ... that your watch would run slower when orbiting a black hole than it would on Earth?
- ... that homing pigeons wouldn't be able to navigate on Mercury because the planet has no magnetic field or atmosphere?
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Photograph credit: Jean-Marc Kuffer
Total internal reflection is the optical phenomenon in which light waves are completely reflected under certain conditions when they arrive at the boundary between one medium and another. This photograph was taken from near the bottom of the shallow end of a swimming pool. The swimmer has disturbed the water surface above her, scrambling the lower half of her reflection, and distorting the reflection of the ladder. Most of the surface is still calm, giving a clear reflection of the tiled bottom of the pool. The air above the water is not visible except at the top of the frame where the angle of incidence of light waves is less than the critical angle and therefore total internal reflection has not occurred.
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These are Good articles, which meet a core set of high editorial standards.
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Flerovium is a synthetic chemical element; it has symbol Fl and atomic number 114. It is an extremely radioactive, superheavy element, named after the Flerov Laboratory of Nuclear Reactions of the Joint Institute for Nuclear Research in Dubna, Russia, where the element was discovered in 1999. The lab's name, in turn, honours Russian physicist Georgy Flyorov (Флёров in Cyrillic, hence the transliteration of "yo" to "e"). IUPAC adopted the name on 30 May 2012. The name and symbol had previously been proposed for element 102 (nobelium) but were not accepted by IUPAC at that time.
It is a transactinide in the p-block of the periodic table. It is in period 7 and is the heaviest known member of the carbon group. Initial chemical studies in 2007–2008 indicated that flerovium was unexpectedly volatile for a group 14 element. More recent results show that flerovium's reaction with gold is similar to that of copernicium, showing it is very volatile and may even be gaseous at standard temperature and pressure. Nonetheless it also seems to show some metallic properties, consistent with it being the heavier homologue of lead. (Full article...) -
Matteucci's frog battery, 1845 (top left); Aldini's frog battery, 1818 (bottom); apparatus for controlled exposure of gases to frog battery (top right).
A frog battery is an electrochemical battery consisting of a number of dead frogs (or sometimes live ones), which form the cells of the battery connected in a series arrangement. It is a kind of biobattery. It was used in early scientific investigations of electricity and academic demonstrations.
The principle behind the battery is the injury potential created in a muscle when it is damaged, although this was not fully understood in the 18th and 19th centuries; the potential being caused incidentally due to the dissection of the frog's muscles. (Full article...) -
A waterspout near Thailand in 2016
A waterspout is a rotating column of air that occurs over a body of water, usually appearing as a funnel-shaped cloud in contact with the water and a cumuliform cloud. There are two types of waterspout, each formed by distinct mechanisms. The most common type is a weak vortex known as a "fair weather" or "non-tornadic" waterspout. The other less common type is simply a classic tornado occurring over water rather than land, known as a "tornadic", "supercellular", or "mesocyclonic" waterspout, and accurately a "tornado over water". A fair weather waterspout has a five-part life cycle: formation of a dark spot on the water surface; spiral pattern on the water surface; formation of a spray ring; development of a visible condensation funnel; and ultimately, decay. Most waterspouts do not suck up water.
While waterspouts form mostly in tropical and subtropical areas, they are also reported in Europe, Western Asia (the Middle East), Australia, New Zealand, the Great Lakes, Antarctica, and on rare occasions, the Great Salt Lake. Some are also found on the East Coast of the United States, and the coast of California. Although rare, waterspouts have been observed in connection with lake-effect snow precipitation bands. (Full article...) -
A bouncing ball. The motion is not quite parabolic due to air resistance.
The physics of a bouncing ball concerns the physical behaviour of bouncing balls, particularly its motion before, during, and after impact against the surface of another body. Several aspects of a bouncing ball's behaviour serve as an introduction to mechanics in high school or undergraduate level physics courses. However, the exact modelling of the behaviour is complex and of interest in sports engineering.
The motion of a ball is generally described by projectile motion (which can be affected by gravity, drag, the Magnus effect, and buoyancy), while its impact is usually characterized through the coefficient of restitution (which can be affected by the nature of the ball, the nature of the impacting surface, the impact velocity, rotation, and local conditions such as temperature and pressure). To ensure fair play, many sports governing bodies set limits on the bounciness of their ball and forbid tampering with the ball's aerodynamic properties. The bounciness of balls has been a feature of sports as ancient as the Mesoamerican ballgame. (Full article...) -
Katharine "Kay" Way (February 20, 1902 – December 9, 1995) was an American physicist best known for her work on the Nuclear Data Project. During World War II, she worked for the Manhattan Project at the Metallurgical Laboratory in Chicago. She became an adjunct professor at Duke University in 1968. (Full article...)
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Arthur Holly Compton (September 10, 1892 – March 15, 1962) was an American physicist who shared the 1927 Nobel Prize in Physics with C. T. R. Wilson for his discovery of the Compton effect, which demonstrated the particle nature of electromagnetic radiation. It was a sensational discovery at the time: the wave nature of light had been well-demonstrated, but the idea that light had both wave and particle properties was not easily accepted. He is also known for his leadership over the Metallurgical Laboratory at the University of Chicago during the Manhattan Project, and served as chancellor of Washington University in St. Louis from 1945 to 1953.
In 1919, Compton was awarded one of the first two National Research Council Fellowships that allowed students to study abroad. He chose to go to the University of Cambridge's Cavendish Laboratory in England, where he studied the scattering and absorption of gamma rays. Further research along these lines led to the discovery of the Compton effect. He used X-rays to investigate ferromagnetism, concluding that it was a result of the alignment of electron spins, and studied cosmic rays, discovering that they were made principally of positively charged particles. (Full article...) -
Facsimile of the Einstein–Szilard letter
The Einstein–Szilard letter was a letter written by Leo Szilard and signed by Albert Einstein on August 2, 1939, that was sent to President of the United States Franklin D. Roosevelt. Written by Szilard in consultation with fellow Hungarian physicists Edward Teller and Eugene Wigner, the letter warned that Germany might develop atomic bombs and suggested that the United States should start its own nuclear program. It prompted action by Roosevelt, which eventually resulted in the Manhattan Project, the development of the first atomic bombs, and the use of these bombs on the cities of Hiroshima and Nagasaki. (Full article...) -
Figure 1. Apparatus used in the Fizeau experiment
The Fizeau experiment was carried out by Hippolyte Fizeau in 1851 to measure the relative speeds of light in moving water. Fizeau used a special interferometer arrangement to measure the effect of movement of a medium upon the speed of light.
According to the theories prevailing at the time, light traveling through a moving medium would be dragged along by the medium, so that the measured speed of the light would be a simple sum of its speed through the medium plus the speed of the medium. Fizeau indeed detected a dragging effect, but the magnitude of the effect that he observed was far lower than expected. When he repeated the experiment with air in place of water he observed no effect. His results seemingly supported the partial aether-drag hypothesis of Augustin-Jean Fresnel, a situation that was disconcerting to most physicists. Over half a century passed before a satisfactory explanation of Fizeau's unexpected measurement was developed with the advent of Albert Einstein's theory of special relativity. Einstein later pointed out the importance of the experiment for special relativity, in which it corresponds to the relativistic velocity-addition formula when restricted to small velocities. (Full article...) -
Schiehallion's isolated position and symmetrical shape were well-suited to the experiment.
The Schiehallion experiment was an 18th-century experiment to determine the mean density of the Earth. Funded by a grant from the Royal Society, it was conducted in the summer of 1774 around the Scottish mountain of Schiehallion, Perthshire. The experiment involved measuring the tiny deflection of the vertical due to the gravitational attraction of a nearby mountain. Schiehallion was considered the ideal location after a search for candidate mountains, thanks to its isolation and almost symmetrical shape.
The experiment had previously been considered, but rejected, by Isaac Newton as a practical demonstration of his theory of gravitation; however, a team of scientists, notably Nevil Maskelyne, the Astronomer Royal, was convinced that the effect would be detectable and undertook to conduct the experiment. The deflection angle depended on the relative densities and volumes of the Earth and the mountain: if the density and volume of Schiehallion could be ascertained, then so could the density of the Earth. Once this was known, it would in turn yield approximate values for those of the other planets, their moons, and the Sun, previously known only in terms of their relative ratios. (Full article...) -
Adriana C. Ocampo Uria (born January 5, 1955) is a Colombian planetary geologist and a Science Program Manager at NASA Headquarters. In 1970, Ocampo emigrated to California and completed her Master in Sciences at California State University, Northridge and finished her PhD at the Vrije Universiteit in the Netherlands. During high school and graduate studies she worked at the Jet Propulsion Laboratory, where she serves as the science coordinator for many planetary missions (Viking, Mars Observer, Voyager, Galileo Galileo Mission, etc.).
She was the first to recognize, using satellite images, that a ring of cenotes or sinkholes, is the only surface impression of the buried Chicxulub crater. This research contributed significantly to the understanding of this impact crater. Ocampo has subsequently led at least seven research expeditions to the Chicxulub site. and to Belize K/Pg ejecta sites, which she discovered and are the subject of her MSc and PhD. She continues to search for new impact craters, and with her team, in 2017, reported on a possible crater near Cali, Colombia. (Full article...) -
Matthew Linzee Sands (October 20, 1919 – September 13, 2014) was an American physicist and educator best known as a co-author of the Feynman Lectures on Physics. A graduate of Rice University, Sands served with the Naval Ordnance Laboratory and the Manhattan Project's Los Alamos Laboratory during World War II.
After the war, Sands studied cosmic rays for his doctorate at the Massachusetts Institute of Technology (MIT) under the supervision of Bruno Rossi. Sands went to the California Institute of Technology (Caltech) in 1950, and helped build and operate its 1.5 GeV electron synchrotron. He became deputy director for the construction and early operation of the Stanford Linear Accelerator Center (SLAC) in 1963. Sands later joined the University of California, Santa Cruz (UCSC) as a professor of physics, and served as its Vice Chancellor for Science from 1969 to 1972. In 1998, The American Physical Society awarded him the Robert R. Wilson Prize "for his many contributions to accelerator physics and the development of electron-positron and proton colliders." (Full article...) -
Styrofoam peanuts clinging to a cat's fur due to static electricity.
The triboelectric effect (also known as triboelectricity, triboelectric charging, triboelectrification, or tribocharging) describes electric charge transfer between two objects when they contact or slide against each other. It can occur with different materials, such as the sole of a shoe on a carpet, or between two pieces of the same material. It is ubiquitous, and occurs with differing amounts of charge transfer (tribocharge) for all solid materials. There is evidence that tribocharging can occur between combinations of solids, liquids and gases, for instance liquid flowing in a solid tube or an aircraft flying through air.
Often static electricity is a consequence of the triboelectric effect when the charge stays on one or both of the objects and is not conducted away. The term triboelectricity has been used to refer to the field of study or the general phenomenon of the triboelectric effect, or to the static electricity that results from it. When there is no sliding, tribocharging is sometimes called contact electrification, and any static electricity generated is sometimes called contact electricity. The terms are often used interchangeably, and may be confused. (Full article...) -
Quantum Reality is a 1985 popular science book by physicist Nick Herbert, a member of the Fundamental Fysiks Group which was formed to explore the philosophical implications of quantum theory. The book attempts to address the ontology of quantum objects, their attributes, and their interactions, without reliance on advanced mathematical concepts. Herbert discusses the most common interpretations of quantum mechanics and their consequences in turn, highlighting the conceptual advantages and drawbacks of each. (Full article...)
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The missing aircraft (9M-MRO) seen in 2011.
The analysis of communications between Malaysia Airlines Flight 370 and Inmarsat's satellite telecommunication network provide the primary source of information about Flight 370's location and possible in-flight events after it disappeared from military radar coverage at 02:22 Malaysia Standard Time (MYT) on 8 March 2014 (17:22 UTC, 7 March), one hour after communication with air traffic control ended and the aircraft departed from its planned flight path while over the South China Sea.
Flight 370 was a scheduled commercial flight with 227 passengers and 12 crew which departed Kuala Lumpur, Malaysia at 0:41 and was scheduled to land in Beijing, China at 6:30 China Standard Time (6:30 MYT; 22:30 UTC, 7 March). Malaysia has worked in conjunction with the Australian Transport Safety Bureau to co-ordinate the analysis, which has also involved the UK's Air Accidents Investigation Branch, Inmarsat, and US National Transportation Safety Board. Other groups have also made efforts to analyse the satellite communications, albeit challenged by a lack of publicly available information for several months after the disappearance. On 29 July 2015, debris was discovered on Réunion Island which was later confirmed to have come from Flight 370; it is the first physical evidence that Flight 370 ended in the Indian Ocean. (Full article...) -
Christiaan Huygens, Lord of Zeelhem, FRS (/ˈhaɪɡənz/ HY-gənz, US also /ˈhɔɪɡənz/ HOY-gənz; Dutch: [ˈkrɪstijaːn ˈɦœyɣə(n)s] ⓘ; also spelled Huyghens; Latin: Hugenius; 14 April 1629 – 8 July 1695) was a Dutch mathematician, physicist, engineer, astronomer, and inventor who is regarded as a key figure in the Scientific Revolution. In physics, Huygens made seminal contributions to optics and mechanics, while as an astronomer he studied the rings of Saturn and discovered its largest moon, Titan. As an engineer and inventor, he improved the design of telescopes and invented the pendulum clock, the most accurate timekeeper for almost 300 years. A talented mathematician and physicist, his works contain the first idealization of a physical problem by a set of mathematical parameters, and the first mathematical and mechanistic explanation of an unobservable physical phenomenon.
Huygens first identified the correct laws of elastic collision in his work De Motu Corporum ex Percussione, completed in 1656 but published posthumously in 1703. In 1659, Huygens derived geometrically the formula in classical mechanics for the centrifugal force in his work De vi Centrifuga, a decade before Isaac Newton. In optics, he is best known for his wave theory of light, which he described in his Traité de la Lumière (1690). His theory of light was initially rejected in favour of Newton's corpuscular theory of light, until Augustin-Jean Fresnel adapted Huygens's principle to give a complete explanation of the rectilinear propagation and diffraction effects of light in 1821. Today this principle is known as the Huygens–Fresnel principle. (Full article...)
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February anniversaries
- 15 February 1564 – Galileo Galilei's birthday
- 18 February 1745 – Alessandro Volta's birthday
- 15 February 1786 – Cat's Eye Nebula discovered
- 18 February 1838 – Ernst Mach's birthday
- 11 February 1847 – Thomas Edison's birthday
- 23 February 1855 – Carl Friedrich Gauss's death
- 22 February 1875 – Heinrich Hertz's birthday
- 28 February 1901 – Linus Pauling's birthday
- 18 February 1967 – J. Robert Oppenheimer's death
- 13 February 1910 – William Shockley's birthday
- 15 February 1988 – Richard Feynman died
- 28 February 2020 – Freeman Dyson's death
General images
The following are images from various physics-related articles on Wikipedia.
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Richard Feynman's Los Alamos ID badge (from History of physics) -
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The first Bose–Einstein condensate observed in a gas of ultracold rubidium atoms. The blue and white areas represent higher density. (from Condensed matter physics) -
The quantum Hall effect: Components of the Hall resistivity as a function of the external magnetic field (from Condensed matter physics) -
Galileo Galilei, early proponent of the modern scientific worldview and method (1564–1642) (from History of physics) -
Classical physics (Rayleigh–Jeans law, black line) failed to explain black-body radiation – the so-called ultraviolet catastrophe. The quantum description (Planck's law, colored lines) is said to be modern physics. (from Modern physics) -
René Descartes (1596–1650) (from History of physics) -
Christiaan Huygens (1629–1695) (from History of physics) -
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William Thomson (Lord Kelvin)
(1824–1907) (from History of physics) -
Daniel Bernoulli (1700–1782) (from History of physics) -
Werner Heisenberg (1901–1976) (from History of physics) -
A composite montage comparing Jupiter (lefthand side) and its four Galilean moons (top to bottom: Io, Europa, Ganymede, Callisto) (from History of physics) -
Alessandro Volta (1745–1827) (from History of physics) -
Johannes Kepler.(1571–1630) (from History of physics) -
Einstein proposed that gravitation is a result of masses (or their equivalent energies) curving ("bending") the spacetime in which they exist, altering the paths they follow within it. (from History of physics) -
An artist's rendition of Kepler-62f, a potentially habitable exoplanet discovered using data transmitted by the Kepler space telescope, named after Kepler. (from History of physics) -
Computer simulation of nanogears made of fullerene molecules. It is hoped that advances in nanoscience will lead to machines working on the molecular scale. (from Condensed matter physics) -
Image of X-ray diffraction pattern from a protein crystal (from Condensed matter physics) -
James Clerk Maxwell (1831–1879) (from History of physics) -
Classical physics is usually concerned with everyday conditions: speeds are much lower than the speed of light, sizes are much greater than that of atoms, yet very small in astronomical terms. Modern physics, however, is concerned with high velocities, small distances, and very large energies. (from Modern physics) -
Star maps by the 11th century Chinese polymath Su Song are the oldest known woodblock-printed star maps to have survived to the present day. This example, dated 1092, employs the cylindricalequirectangular projection. (from History of physics) -
Heike Kamerlingh Onnes and Johannes van der Waals with the helium liquefactor at Leiden in 1908 (from Condensed matter physics) -
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A magnet levitating above a high-temperature superconductor. Today some physicists are working to understand high-temperature superconductivity using the AdS/CFT correspondence. (from Condensed matter physics) -
A Feynman diagram representing (left to right) the production of a photon (blue sine wave) from the annihilation of an electron and its complementary antiparticle, the positron. The photon becomes a quark–antiquark pair and a gluon (green spiral) is released. (from History of physics) -
Gottfried Leibniz (1646–1716) (from History of physics) -
Ludwig Boltzmann (1844–1906) (from History of physics) -
The Standard Model (from History of physics) -
Michael Faraday (1791–1867) (from History of physics) -
Sir Isaac Newton (1642–1727) (from History of physics) -
The Hindu-Arabic numeral system. The inscriptions on the edicts of Ashoka (3rd century BCE) display this number system being used by the Imperial Mauryas. (from History of physics) -
Rudolf Clausius (1822–1888) (from History of physics) -
Marie Skłodowska-Curie
(1867–1934) was awarded two Nobel prizes, Physics (1903) and Chemistry (1911) (from History of physics) -
Max Planck (1858–1947) (from History of physics) -
Chien-Shiung Wu worked on parity violation in 1956 and announced her results in January 1957. (from History of physics) -
The ancient Greek mathematician Archimedes, developer of ideas regarding fluid mechanics and buoyancy. (from History of physics) -
One possible signature of a Higgs boson from a simulated proton–proton collision. It decays almost immediately into two jets of hadrons and two electrons, visible as lines. (from History of physics) -
Albert Einstein (1879–1955), photographed here in around 1905 (from History of physics) -
J. J. Thomson (1856–1940) discovered the electron and isotopy and also invented the mass spectrometer. He was awarded the Nobel Prize in Physics in 1906. (from History of physics) -
The Polish astronomer Nicolaus Copernicus (1473–1543) is remembered for his development of a heliocentric model of the Solar System. (from History of physics) -
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Physics topics
Classical physics traditionally includes the fields of mechanics, optics, electricity, magnetism, acoustics and thermodynamics. The term Modern physics is normally used for fields which rely heavily on quantum theory, including quantum mechanics, atomic physics, nuclear physics, particle physics and condensed matter physics. General and special relativity are usually considered to be part of modern physics as well.
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