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. It 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 magnetosphere of Jupiter is the cavity created in the solar wind by Jupiter's magnetic field. Extending up to seven million kilometers in the Sun's direction and almost to the orbit of Saturn in the opposite direction, Jupiter's magnetosphere is the largest and most powerful of any planetary magnetosphere in the Solar System, and by volume the largest known continuous structure in the Solar System after the heliosphere. Wider and flatter than the Earth's magnetosphere, Jupiter's is stronger by an order of magnitude, while its magnetic moment is roughly 18,000 times larger. The existence of Jupiter's magnetic field was first inferred from observations of radio emissions at the end of the 1950s and was directly observed by the Pioneer 10 spacecraft in 1973.
Jupiter's internal magnetic field is generated by electrical currents in the planet's outer core, which is theorized to be composed of liquid metallic hydrogen. Volcanic eruptions on Jupiter's moon Io eject large amounts of sulfur dioxide gas into space, forming a large torus around the planet. Jupiter's magnetic field forces the torus to rotate with the same angular velocity and direction as the planet. The torus in turn loads the magnetic field with plasma, in the process stretching it into a pancake-like structure called a magnetodisk. In effect, Jupiter's magnetosphere is internally driven, shaped primarily by Io's plasma and its own rotation, rather than by the solar wind as at Earth's magnetosphere. Strong currents in the magnetosphere generate permanent aurorae around the planet's poles and intense variable radio emissions, which means that Jupiter can be thought of as a very weak radio pulsar. Jupiter's aurorae have been observed in almost all parts of the electromagnetic spectrum, including infrared, visible, ultraviolet and soft X-rays. (Full article...)
Did you know -
- ...that if you ever saw Jupiter's magnetic field from Earth, it would appear five times larger than the full moon?
- ...that the impact of a raindrop would be fatal if not for the property of fluid flow known as terminal velocity?
- ...that transits of Venus occur in a 243-year cycle?
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The Feynman Lectures on Physics is a 1964 physics textbook by Richard P. Feynman, Robert B. Leighton and Matthew Sands, based upon the lectures given by Feynman to undergraduate students at the California Institute of Technology (Caltech) in 1961–63.
It includes lectures on mathematics, electromagnetism, Newtonian physics, quantum physics, and the relation of physics to other sciences. Six readily accessible chapters were later compiled into a book entitled Six Easy Pieces: Essentials of Physics Explained by Its Most Brilliant Teacher, and six more in Six Not So Easy Pieces: Einstein's Relativity, Symmetry and Space-Time.
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Deep Impact was a NASA space probe launched from Cape Canaveral Air Force Station on January 12, 2005. It was designed to study the interior composition of the comet Tempel 1 (9P/Tempel), by releasing an impactor into the comet. At 05:52 UTC on July 4, 2005, the Impactor successfully collided with the comet's nucleus. The impact excavated debris from the interior of the nucleus, forming an impact crater. Photographs taken by the spacecraft showed the comet to be more dusty and less icy than had been expected. The impact generated an unexpectedly large and bright dust cloud, obscuring the view of the impact crater.
Previous space missions to comets, such as Giotto, Deep Space 1, and Stardust, were fly-by missions. These missions were able to photograph and examine only the surfaces of cometary nuclei, and even then from considerable distances. The Deep Impact mission was the first to eject material from a comet's surface, and the mission garnered considerable publicity from the media, international scientists, and amateur astronomers alike. (Full article...) -
Figure 1: The Molniya orbit. Usually the period from perigee +2 hours to perigee +10 hours is used to transmit to the northern hemisphere.
A Molniya orbit (Russian: Молния, IPA: [ˈmolnʲɪjə] ⓘ, "Lightning") is a type of satellite orbit designed to provide communications and remote sensing coverage over high latitudes. It is a highly elliptical orbit with an inclination of 63.4 degrees, an argument of perigee of 270 degrees, and an orbital period of approximately half a sidereal day. The name comes from the Molniya satellites, a series of Soviet/Russian civilian and military communications satellites which have used this type of orbit since the mid-1960s. A variation on the Molniya orbit is the so-called Three Apogee (TAP) orbit, whose period is a third of a sidereal day.
The Molniya orbit has a long dwell time over the hemisphere of interest, while moving very quickly over the other. In practice, this places it over either Russia or Canada for the majority of its orbit, providing a high angle of view to communications and monitoring satellites covering these high-latitude areas. Geostationary orbits, which are necessarily inclined over the equator, can only view these regions from a low angle, hampering performance. In practice, a satellite in a Molniya orbit serves the same purpose for high latitudes as a geostationary satellite does for equatorial regions, except that multiple satellites are required for continuous coverage. (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...) -
Harley D. Rutledge (January 10, 1926 – June 5, 2006) was an American physicist and ufologist. He earned a doctorate in solid-state physics from the University of Missouri and spent nearly two decades as chair of the physics department at Southeast Missouri State University. In the 1970s Rutledge directed Project Identification, a long-term field investigation of unidentified aerial phenomena in Missouri that was reported as the first sustained scientific study of UFOs. The project involved trained observers and technical instruments, and his findings were published in the 1981 book Project Identification: The First Scientific Study of UFO Phenomena. Though widely recognized as a UFO expert and frequent media commentator, Rutledge emphasized that many sightings had conventional explanations. (Full article...) -
The universe is all of space and time and their contents. It comprises all of existence, any fundamental interaction, physical process and physical constant, and therefore all forms of matter and energy, and the structures they form, from sub-atomic particles to entire galactic filaments. Since the early 20th century, the field of cosmology establishes that space and time emerged together at the Big Bang 13.787±0.020 billion years ago and that the universe has been expanding since then. The portion of the universe that can be seen by humans is approximately 93 billion light-years in diameter at present, but the total size of the universe is not known.
Some of the earliest cosmological models of the universe were geocentric, placing Earth at the center. During the European Scientific Revolution, astronomical observations led to a heliocentric model. Further observational improvements led to the realization that the Sun is one of a few hundred billion stars in the Milky Way, which is one of a few hundred billion galaxies in the observable universe. Many of the stars in a galaxy have planets. At the largest scale, galaxies are distributed uniformly and the same in all directions, meaning that the universe has neither an edge nor a center. At smaller scales, galaxies are distributed in clusters and superclusters, which form immense filaments and voids in space, creating a vast foam-like structure. Discoveries in the early 20th century lead to the Big Bang theory with a hot fireball, cooling and becoming less dense as the universe expanded, allowing the first subatomic particles and simple atoms to form. Giant clouds of hydrogen and helium were gradually drawn to the places where matter was most dense, forming the first galaxies, stars, and everything else seen today. (Full article...) -
Foster's reactance theorem is an important theorem in the fields of electrical network analysis and synthesis. The theorem states that the reactance of a passive, lossless two-terminal (one-port) network always strictly monotonically increases with frequency. It is easily seen that the reactances of inductors and capacitors individually increase or decrease with frequency respectively and from that basis a proof for passive lossless networks generally can be constructed. The proof of the theorem was presented by Ronald Martin Foster in 1924, although the principle had been published earlier by Foster's colleagues at American Telephone & Telegraph.
The theorem can be extended to admittances and the encompassing concept of immittances. A consequence of Foster's theorem is that zeros and poles of the reactance must alternate with frequency. Foster used this property to develop two canonical forms for realising these networks. Foster's work was an important starting point for the development of network synthesis. (Full article...) -
An extratropical cyclone near Iceland
In meteorology, a cyclone (/ˈsaɪ.kloʊn/) is a large air mass that rotates around a strong center of low atmospheric pressure, counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere as viewed from above (opposite to an anticyclone). Cyclones are characterized by inward-spiraling winds that rotate about a zone of low pressure.
Cyclones have also been seen on planets other than the Earth, such as Mars, Jupiter, and Neptune. Cyclogenesis is the process of cyclone formation and intensification. (Full article...) -
Norris Edwin Bradbury (May 30, 1909 – August 20, 1997) was an American physicist who served as director of the Los Alamos National Laboratory for 25 years from 1945 to 1970. He succeeded Robert Oppenheimer, who personally chose Bradbury for the position of director after working closely with him on the Manhattan Project during World War II. Bradbury was in charge of the final assembly of "the Gadget", detonated in July 1945 for the Trinity test.
Bradbury took charge at Los Alamos at a difficult time. Staff were leaving in droves, living conditions were poor and there was a possibility that the laboratory would close. He managed to persuade enough staff to stay and got the University of California to renew the contract to manage the laboratory. He pushed continued development of nuclear weapons, transforming them from laboratory devices to production models. Numerous improvements made them safer, more reliable and easier to store and handle, and made more efficient use of scarce fissionable materiel. (Full article...) -
A near infrared time lapse of the upper atmosphere of Uranus, taken by the James Webb Space Telescope. Blue represents the planet's lower atmosphere, while red represents higher altitudes.
The atmosphere of Uranus is composed primarily of hydrogen and helium. At depth, it is significantly enriched in volatiles (dubbed "ices") such as water, ammonia, and methane. The opposite is true for the upper atmosphere, which contains very few gases heavier than hydrogen and helium due to its low temperature. Uranus's atmosphere is the coldest of all the planets, with its temperature reaching as low as 49 K.
The Uranian atmosphere can be divided into three main layers: the troposphere, between altitudes of −300 and 50 km and pressures from 100 to 0.1 bar; the stratosphere, spanning altitudes between 50 and 4000 km and pressures of between 0.1 and 10−10 bar; and the hot thermosphere (and exosphere) extending from an altitude of 4,000 km to several Uranian radii from the nominal surface at 1 bar pressure. Unlike Earth's, Uranus's atmosphere has no mesosphere. (Full article...) -
A computed tomography scan (CT scan), formerly called computed axial tomography scan (CAT scan), is a medical imaging technique used to obtain detailed internal images of the body. The personnel that perform CT scans are called radiographers or radiology technologists.
CT scanners use a rotating X-ray tube and a row of detectors placed in a gantry to measure X-ray attenuations by different tissues inside the body. The multiple X-ray measurements taken from different angles are then processed on a computer using tomographic reconstruction algorithms to produce tomographic (cross-sectional) images (virtual "slices") of a body. CT scans can be used in patients with metallic implants or pacemakers, for whom magnetic resonance imaging (MRI) is contraindicated. (Full article...) -
Kenneth Tompkins Bainbridge (July 27, 1904 – July 14, 1996) was an American physicist at Harvard University who worked on cyclotron research. His accurate measurements of mass differences between nuclear isotopes allowed him to confirm Albert Einstein's mass–energy equivalence concept. He was the Director of the Manhattan Project's Trinity nuclear test, which took place July 16, 1945. Bainbridge described the Trinity explosion as a "foul and awesome display". He remarked to J. Robert Oppenheimer immediately after the test, "Now we are all sons of bitches." This marked the beginning of his dedication to ending the testing of nuclear weapons and to efforts to maintain civilian control of future developments in that field. (Full article...) -
Condensed matter physics is the field of physics that deals with the macroscopic and microscopic physical properties of matter, especially the solid and liquid phases, that arise from electromagnetic forces between atoms and electrons. More generally, the subject deals with condensed phases of matter: systems of many constituents with strong interactions among them. More exotic condensed phases include the superconducting phase exhibited by certain materials at extremely low cryogenic temperatures, the ferromagnetic and antiferromagnetic phases of spins on crystal lattices of atoms, the Bose–Einstein condensates found in ultracold atomic systems, and liquid crystals. Condensed matter physicists seek to understand the behavior of these phases by experiments to measure various material properties, and by applying the physical laws of quantum mechanics, electromagnetism, statistical mechanics, and other physics theories to develop mathematical models and predict the properties of extremely large groups of atoms.
The diversity of systems and phenomena available for study makes condensed matter physics the most active field of contemporary physics: one third of all American physicists self-identify as condensed matter physicists, and the Division of Condensed Matter Physics is the largest division of the American Physical Society. These include solid state and soft matter physicists, who study quantum and non-quantum physical properties of matter respectively. Both types study a great range of materials, providing many research, funding and employment opportunities. The field overlaps with chemistry, materials science, engineering and nanotechnology, and relates closely to atomic physics and biophysics. The theoretical physics of condensed matter shares important concepts and methods with that of particle physics and nuclear physics. (Full article...) -
Grete Hermann (2 March 1901 – 15 April 1984) was a German mathematician, philosopher, theoretical physicist, writer, and educator. She is known for her foundational work in quantum mechanics and computer algebra; her writings on political philosophy; and her work with the Internationaler Sozialistischer Kampfbund (ISK) in opposition to Nazism.
Hermann worked on reconciling the neo-Kantian conception of causality with quantum mechanics. This work led to her critique of Von Neumann's no hidden variables proof. Her criticism was long ignored; it was discovered in 1974 by Max Jammer who publicized it. In 1936, Hermann shared in the award of the Richard Avenarius prize. She was the first graduate student of Emmy Noether and she published the posthumous works of others, including that of Leonard Nelson. (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...) -
The Paranal Observatory of European Southern Observatory creating a laser guide star in the atmosphere to observe the Galactic Center
Astronomy is a natural science that studies celestial objects and the phenomena that occur in the cosmos. It uses mathematics, physics, and chemistry to explain their origin and their overall evolution. Objects of interest include planets, moons, stars, nebulae, galaxies, meteoroids, asteroids, and comets. Relevant phenomena include supernova explosions, gamma ray bursts, quasars, blazars, pulsars, and cosmic microwave background radiation. More generally, astronomy studies everything that originates beyond Earth's atmosphere. Cosmology is the branch of astronomy that studies the universe as a whole.
Astronomy is one of the oldest natural sciences. The early civilizations in recorded history made methodical observations of the night sky. These include the Egyptians, Babylonians, Greeks, Indians, Chinese, Maya, and many ancient indigenous peoples of the Americas. In the past, astronomy included disciplines as diverse as astrometry, celestial navigation, observational astronomy, and the making of calendars. (Full article...)
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March anniversaries
- 1 March 1966 – first spacecraft crash-lands on Venus
- 14 March 1879 – Albert Einstein's birthday
- 14 March 2018 – Stephen Hawking died
- 20 March 1942 - Gabriele Veneziano's Birthday
- 24 March 1993 – Comet Shoemaker–Levy 9 discovered
General images
The following are images from various physics-related articles on Wikipedia.
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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) -
Christiaan Huygens (1629–1695) (from History of physics) -
1927 Solvay Conference included prominent physicists Albert Einstein, Werner Heisenberg, Max Planck, Hendrik Lorentz, Niels Bohr, Marie Curie, Erwin Schrödinger, Paul Dirac (from History of physics) -
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) -
An engraving of Benjamin Franklin's kite experiment used to study lightning. (from History of physics) -
Richard Feynman's Los Alamos ID badge (from History of 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) -
Johannes Kepler's first law of planetary motion states that planets move in elliptical orbits about the Sun. (from History of physics) -
Sir Isaac Newton (1642–1727) (from History of physics) -
Marie Skłodowska-Curie
(1867–1934) received Nobel prizes in physics (1903) and chemistry (1911). (from History of physics) -
Chien-Shiung Wu worked on parity violation in 1956 and announced her results in January 1957. (from History of physics) -
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The Voltaic pile, the first battery was invented by Alessandro Volta in 1800 (from History of physics) -
Hydrogen emission spectrum is discrete (here in log scale). The lines can only be explained with quantum mechanics. (from History of physics) -
The Standard Model (from History of physics) -
The quantum Hall effect: Components of the Hall resistivity as a function of the external magnetic field (from Condensed matter physics) -
Magdeburg hemispheres, an experiment by Otto von Guericke where two metal hemispheres are held together by vacuum and cannot be separated even if large forces are applied. (from History of physics) -
Newton's cannonball, a though experiment by Newton relating the motion of a projectile and orbiting of planets. (from History of physics) -
Einstein proposed that gravitation results from masses (or their equivalent energies) curving ("bending") the spacetime in which they exist, altering the paths they follow within it. (from History of physics) -
Image of X-ray diffraction pattern from a protein crystal (from Condensed matter 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 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) -
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Heike Kamerlingh Onnes and Johannes van der Waals with the helium liquefactor at Leiden in 1908 (from Condensed matter physics) -
James Prescott Joule's apparatus for measuring the mechanical equivalent of heat which the "work" of the falling weight is converted into the "heat" of agitation in the water. (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) -
Composite montage comparing Jupiter (left) and its four Galilean moons (from top: Io, Europa, Ganymede, Callisto) (from History of physics) -
Crookes tube used to study cathode rays. It led to the discovery of the electron by J. J. Thomson. (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) -
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) -
Maxwell's demon, thought experiment by James Clerk Maxwell to describe the kinetic theory of gases and describe how a microscopic creature could lead to violations of the second law of thermodynamics. (from History of physics) -
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The ancient Greek mathematician Archimedes, developer of ideas regarding fluid mechanics and buoyancy. (from History of physics) -
Albert Einstein (1879–1955), ca. 1905 (from History of physics) -
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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) -
Galileo Galilei (1564–1642), early proponent of the modern scientific worldview and method (from History of physics)
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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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