Mass
Mass is both a property of a physical body and a measure of its resistance to acceleration when a net force is applied. The object's mass determines the strength of its gravitational attraction to other bodies; the basic SI unit of mass is the kilogram. In physics, mass is not the same as weight though mass is determined by measuring the object's weight using a spring scale, rather than balance scale comparing it directly with known masses. An object on the Moon would weigh less than it does on Earth because of the lower gravity, but it would still have the same mass; this is because weight is a force, while mass is the property that determines the strength of this force. There are several distinct phenomena. Although some theorists have speculated that some of these phenomena could be independent of each other, current experiments have found no difference in results regardless of how it is measured: Inertial mass measures an object's resistance to being accelerated by a force. Active gravitational mass measures the gravitational force exerted by an object.
Passive gravitational mass measures the gravitational force exerted on an object in a known gravitational field. The mass of an object determines its acceleration in the presence of an applied force; the inertia and the inertial mass describe the same properties of physical bodies at the qualitative and quantitative level by other words, the mass quantitatively describes the inertia. According to Newton's second law of motion, if a body of fixed mass m is subjected to a single force F, its acceleration a is given by F/m. A body's mass determines the degree to which it generates or is affected by a gravitational field. If a first body of mass mA is placed at a distance r from a second body of mass mB, each body is subject to an attractive force Fg = GmAmB/r2, where G = 6.67×10−11 N kg−2 m2 is the "universal gravitational constant". This is sometimes referred to as gravitational mass. Repeated experiments since the 17th century have demonstrated that inertial and gravitational mass are identical.
The standard International System of Units unit of mass is the kilogram. The kilogram is 1000 grams, first defined in 1795 as one cubic decimeter of water at the melting point of ice. However, because precise measurement of a decimeter of water at the proper temperature and pressure was difficult, in 1889 the kilogram was redefined as the mass of the international prototype kilogram of cast iron, thus became independent of the meter and the properties of water. However, the mass of the international prototype and its identical national copies have been found to be drifting over time, it is expected that the re-definition of the kilogram and several other units will occur on May 20, 2019, following a final vote by the CGPM in November 2018. The new definition will use only invariant quantities of nature: the speed of light, the caesium hyperfine frequency, the Planck constant. Other units are accepted for use in SI: the tonne is equal to 1000 kg. the electronvolt is a unit of energy, but because of the mass–energy equivalence it can be converted to a unit of mass, is used like one.
In this context, the mass has units of eV/c2. The electronvolt and its multiples, such as the MeV, are used in particle physics; the atomic mass unit is 1/12 of the mass of a carbon-12 atom 1.66×10−27 kg. The atomic mass unit is convenient for expressing the masses of molecules. Outside the SI system, other units of mass include: the slug is an Imperial unit of mass; the pound is a unit of both mass and force, used in the United States. In scientific contexts where pound and pound need to be distinguished, SI units are used instead; the Planck mass is the maximum mass of point particles. It is used in particle physics; the solar mass is defined as the mass of the Sun. It is used in astronomy to compare large masses such as stars or galaxies; the mass of a small particle may be identified by its inverse Compton wavelength. The mass of a large star or black hole may be identified with its Schwarzschild radius. In physical science, one may distinguish conceptually between at least seven different aspects of mass, or seven physical notions that involve the concept of mass.
Every experiment to date has shown these seven values to be proportional, in some cases equal, this proportionality gives rise to the abstract concept of mass. There are a number of ways mass can be measured or operationally defined: Inertial mass is a measure of an object's resistance to acceleration when a force is applied, it is determined by applying a force to an object and measuring the acceleration that results from that force. An object with small inertial mass will accelerate more than an object with large inertial mass when acted upon by the same force. One says. Active gravitational mass is a measure of the strength of an object's gravitational flux. Gravitational field can be measured by allowing a small "test object" to fall and measuring its free-fall acceleration. For example, an object in free fall near the Moon is subject to a smaller gravitational field, hence
Thalassa (moon)
Thalassa known as Neptune IV, is the second-innermost satellite of Neptune. Thalassa was named after a daughter of Aether and Hemera from Greek mythology. "Thalassa" is the Greek word for "sea". Thalassa was discovered sometime before mid-September 1989 from the images taken by the Voyager 2 probe, it was given the temporary designation S/1989 N 5. The discovery was announced on September 29, 1989, mentions "25 frames taken over 11 days", implying a discovery date of sometime before September 18; the name was given on 16 September 1991. Thalassa shows no sign of any geological modification, it is that it is a rubble pile re-accreted from fragments of Neptune's original satellites, which were smashed up by perturbations from Triton soon after that moon's capture into a eccentric initial orbit. Unusually for irregular bodies, it appears to be disk-shaped. Since the Thalassian orbit is below Neptune's synchronous orbit radius, it is spiralling inward due to tidal deceleration and may impact Neptune's atmosphere, or break up into a planetary ring upon passing its Roche limit due to tidal stretching.
Soon after, the spreading debris may impinge upon Despina's orbit. Thalassa Profile by NASA's Solar System Exploration Neptune's Known Satellites
Hippocamp (moon)
Hippocamp known as S/2004 N 1, is a small moon of Neptune, about 35 km in diameter, which orbits the planet in just under one Earth day. Its discovery on 1 July 2013 increased the number of Neptune's known satellites to fourteen; the moon is so dim that it was not observed when the Voyager 2 space probe flew by Neptune and its moons in 1989. Mark Showalter of the SETI Institute found it by analyzing archived Neptune photographs the Hubble Space Telescope captured between 2004 and 2009; the moon was formally numbered Neptune XIV on 25 September 2018 in Minor Planet Circular 111804, named Hippocamp in February 2019. Mark Showalter discovered Hippocamp on 1 July 2013 while examining Hubble Space Telescope images of Neptune's ring arcs from 2009, he used a technique similar to panning to compensate for orbital motion and allow stacking of multiple images to bring out faint details. After deciding "on a whim" to expand the search area to radii well beyond the rings, he found the "fairly obvious dot" that represented the new moon.
He found it in other archival HST images going back to 2004. Voyager 2, which had observed all of Neptune's other inner satellites, did not detect it during its 1989 flyby, due to its dimness. Given that the relevant images have long been available to the public, the discovery could have been made by anyone. Hippocamp is the first moon of Neptune to be discovered since September 2003, when Psamathe was discovered. Neptune's largest moon, has a retrograde and inclined orbit, it is hypothesized that Neptune captured it from the Kuiper belt well after Neptune's original satellite system formed. The pre-existing moons' orbits would have been shifted by this event, leading to the ejection of some moons and the collisional destruction of others. At least some of Neptune's present inner satellites are thought to have accreted from the resulting rubble after Triton's orbit was circularized by tidal deceleration. Another hypothesis suggests that Hippocamp may have formed out of debris from the nearest moon of Neptune, the much larger Proteus.
The debris was ejected by the comet impact that formed its largest crater Pharos. Hippocamp orbits close to Proteus. Hippocamp formed within a few thousand kilometres from Proteus. Hippocamp is assumed to resemble Neptune's other inner satellites in having a surface as dark as "dirty asphalt", their geometrical albedos range from 0.07 to 0.10. Derived from Hippocamp's apparent magnitude of 26.5, its diameter was thought to be around 16 to 20 km, making it the smallest of Neptune's known moons. More recent observations of Neptune's moons have shown that Hippocamp is twice as large as thought, giving it a diameter of 34.8 km. However, it remains by a wide margin the smallest of Neptune's inner, satellites; the near-infrared spectra of Neptune's rings and inner moons have been examined with the HST NICMOS instrument. Similar dark, reddish material, characteristic of small outer Solar System bodies, appears to be present on all their surfaces; the data is consistent with organic compounds containing C−H and/or C≡N bonds, but spectral resolution was inadequate to identify the molecules.
Water ice, abundant in the outer Solar System, is believed to be present, but its spectral signature could not be observed. Hippocamp completes one revolution around Neptune every 22 hours and 28.1 minutes, implying a semi-major axis, or orbital distance of 105,283 km, just over a quarter that of Earth's Moon, twice the average radius of Neptune's rings. Both its inclination and eccentricity are close to zero, it orbits between Larissa and Proteus, making it the second outermost of Neptune's regular satellites. Its small size at this location runs counter to a trend among the other regular Neptunian satellites of increasing diameter with increasing distance from the primary; the periods of Larissa and Hippocamp are within about one percent of a 3:5 orbital resonance, while Hippocamp and Proteus are within 0.1% of a 5:6 resonance. Larissa and Proteus are thought to have passed through a 1:2 mean-motion resonance a few hundred million years ago. Proteus and Hippocamp have drifted away from Larissa since because the former two are outside Neptune-synchronous orbit and are thus being tidally accelerated, while Larissa is within and is being tidally decelerated.
The moon is named after the Hippocamp, a mythological creature, half horse and half fish in Greek mythology. When the moon was numbered as Neptune XIV, it remained without an official name until February 2019; the discovery team decided to submit a name proposal to the International Astronomical Union based on a figure from Greco-Roman mythology with a relationship to Poseidon or Neptune, the god of the sea, consistent with the naming of other moons of Neptune. Among the names considered was Polyphemus, the gigantic one-eyed son of Poseidon and Thoosa. Showalter, the lead of the discovery team, chose the name Hippocamp in acknowledgement of the seahorse genus and the mythological creature, aptly part horse and part fish. In 2019, the IAU accepted the name Hippocamp. Media related to Hippocamp at Wikimedia Commons
Space probe
A space probe is a robotic spacecraft that does not orbit Earth, but instead, explores further into outer space. A space probe may approach the Moon; the space agencies of the USSR, the United States, the European Union, China,India, Israel have collectively launched probes to several planets and moons of the Solar System, as well as to a number of asteroids and comets. 15 missions are operational. Once a probe has left the vicinity of Earth, its trajectory will take it along an orbit around the Sun similar to the Earth's orbit. To reach another planet, the simplest practical method is a Hohmann transfer orbit. More complex techniques, such as gravitational slingshots, can be more fuel-efficient, though they may require the probe to spend more time in transit; some high Delta-V missions can only be performed, within the limits of modern propulsion, using gravitational slingshots. A technique using little propulsion, but requiring a considerable amount of time, is to follow a trajectory on the Interplanetary Transport Network.
First man-made object to any other extra terrestrial surface. First mission to photograph the far side of the Moon, launched in 1959. First robotic sample return probe from the Moon. First rover on Moon, it was sent to the Moon on November 10, 1970. First probe to Mercury. First successful in-place analysis of another planet, it may have been the first space probe to impact the surface of another planet, although it is unclear whether it reached Venus' surface. The Venera 7 probe was the first spacecraft to soft land on another planet and to transmit data from there back to Earth. Upon its arrival at Mars on November 13, 1971, Mariner 9 became the first space probe to maintain orbit around another planet. First soft landing on Mars The lander began transmitting to the Mars 3 orbiter 90 seconds after landing. After 20 seconds, transmission stopped for unknown reasons. First successful rover on Mars; the Mars Exploration Rovers and Opportunity landed on Mars to explore the Martian surface and geology, searched for clues to past water activity on Mars.
They were each launched in 2003 and landed in 2004. Communication with Spirit stopped on sol 2210. JPL continued to attempt to regain contact until May 24, 2011, when NASA announced that efforts to communicate with the unresponsive rover had ended. Opportunity arrived at Endeavour crater on 9 August 2011, at a landmark called Spirit Point named after its rover twin, after traversing 13 miles from Victoria crater, over a three-year period. After a planet wide dust storm in June 2018, the final communication was received on June 10, 2018, Opportunity was declared dead on February 13, 2019; the rover lasted for fifteen years on Mars — although the rover was intended to last only three months. The first dedicated missions to a comet, it was the first massive international coordination of space probes on an interplanetary mission, with probes launched by the Soviet Space Agency, European Space Agency, Japan's ISAS. A solar observatory in the International Sun-Earth Explorer series, it was sent into solar orbit to make the first close observations of a comet, Comet Giacobini–Zinner, in 1985 as a prelude to studies of Halley's Comet.
Two Russian/French spacecraft. They dropped balloons at Venus before their rendezvous with Halley's Comet; this Japanese probe was the first non-Soviet interplanetary probe. A second Japanese probe, it made ultraviolet wavelength observations of the comet; the first space probe to take close-up images of its nucleus. First solar wind sample return probe from sun-earth L1. First sample return probe from a comet tail. First probe to land on an asteroid. First sample return probe to launch from an asteroid; the Rosetta space probe flew by two asteroids and made a rendezvous and orbited comet 67P/Churyumov-Gerasimenko in November 2014. First probe to Jupiter. Radio communications were lost with Pioneer 10 on January 23, 2003, because of the loss of electric power for its radio transmitter, with the probe at a distance of 12 billion kilometers from Earth. First probe to fly by Saturn. Voyager 1 is a 733-kilogram probe launched September 5, 1977, it visited Jupiter and Saturn and was the first probe to provide detailed images of the moons of these planets.
Voyager 1 is the farthest human-made object from Earth, traveling away from both the Earth and the Sun at a faster speed than any other probe. As of September 12, 2013, Voyager 1 is about 12 billion miles from the Sun. On August 25, 2012, Voyager 1 became. Voyager 1 has not had a functioning plasma sensor since 1980, but a solar flare in 2012 allowed scientists from NASA to measure vibrations of the plasma surrounding the craft; the vibrations allowed scientists to measure the plasma to be much denser than measurements taken in the far layers of our heliosphere, thus concluding the craft had broken beyond the heliopause. Voyager 2 was launched by NASA on August 20, 1977; the probe's primary mission was to visit the ice giants and Neptune, which it completed on October 2, 1989. It is the only probe to have visited the ice giants, it is the four
Computer simulation
Computer simulation is the reproduction of the behavior of a system using a computer to simulate the outcomes of a mathematical model associated with said system. Since they allow to check the reliability of chosen mathematical models, computer simulations have become a useful tool for the mathematical modeling of many natural systems in physics, climatology, chemistry and manufacturing, human systems in economics, social science, health care and engineering. Simulation of a system is represented as the running of the system's model, it can be used to explore and gain new insights into new technology and to estimate the performance of systems too complex for analytical solutions. Computer simulations are realized by running computer programs that can be either small, running instantly on small devices, or large-scale programs that run for hours or days on network-based groups of computers; the scale of events being simulated by computer simulations has far exceeded anything possible using traditional paper-and-pencil mathematical modeling.
Over 10 years ago, a desert-battle simulation of one force invading another involved the modeling of 66,239 tanks and other vehicles on simulated terrain around Kuwait, using multiple supercomputers in the DoD High Performance Computer Modernization Program. Other examples include a 1-billion-atom model of material deformation; because of the computational cost of simulation, computer experiments are used to perform inference such as uncertainty quantification. A computer model is the algorithms and equations used to capture the behavior of the system being modeled. By contrast, computer simulation is the actual running of the program that contains these equations or algorithms. Simulation, therefore, is the process of running a model, thus one would not "build a simulation". Computer simulation developed hand-in-hand with the rapid growth of the computer, following its first large-scale deployment during the Manhattan Project in World War II to model the process of nuclear detonation, it was a simulation of 12 hard spheres using a Monte Carlo algorithm.
Computer simulation is used as an adjunct to, or substitute for, modeling systems for which simple closed form analytic solutions are not possible. There are many types of computer simulations; the external data requirements of simulations and models vary widely. For some, the input might be just a few numbers, while others might require terabytes of information. Input sources vary widely: Sensors and other physical devices connected to the model. Lastly, the time at which data is available varies: "invariant" data is built into the model code, either because the value is invariant or because the designers consider the value to be invariant for all cases of interest; because of this variety, because diverse simulation systems have many common elements, there are a large number of specialized simulation languages. The best-known may be Simula. There are now many others. Systems that accept data from external sources must be careful in knowing what they are receiving. While it is easy for computers to read in values from text or binary files, what is much harder is knowing what the accuracy of the values are.
They are expressed as "error bars", a minimum and maximum deviation from the value range within which the true value lie. Because digital computer mathematics is not perfect and truncation errors multiply this error, so it is useful to perform an "error analysis" to confirm that values output by the simulation will still be usefully accurate. Small errors in the original data can accumulate into substantial error in the simulation. While all computer analysis is subject to the "GIGO" restriction, this is true of digital simulation. Indeed, observation of this inherent, cumulative error in digital systems was the main catalyst for the development of chaos theory. Computer models can be classified according to several independent pairs of attributes, including: Stochastic or deterministic – see external links below for examples of stochastic vs. deterministic simulations Steady-state or dynamic Continuous or discrete Dynamic system simulation, e.g. electric systems, hydraulic systems or multi-body mechanical s
Triton (moon)
Triton is the largest natural satellite of the planet Neptune, the first Neptunian moon to be discovered. The discovery was made on October 1846, by English astronomer William Lassell, it is the only large moon in the Solar System with a retrograde orbit, an orbit in the direction opposite to its planet's rotation. At 2,710 kilometres in diameter, it is the seventh-largest moon in the Solar System, the only satellite of Neptune massive enough to be in hydrostatic equilibrium and the second-largest planetary moon in relation to its primary, after Earth's Moon; because of its retrograde orbit and composition similar to Pluto's, Triton is thought to have been a dwarf planet captured from the Kuiper belt. It has a surface of frozen nitrogen, a water-ice crust, an icy mantle and a substantial core of rock and metal; the core makes up two-thirds of its total mass. The mean density is 2.061 g/cm3, reflecting a composition of 15–35% water ice. Triton is one of the few moons in the Solar System known to be geologically active.
As a consequence, its surface is young, with few obvious impact craters. Intricate cryovolcanic and tectonic terrains suggest a complex geological history. Part of its surface has geysers erupting sublimated nitrogen gas, contributing to a tenuous nitrogen atmosphere less than 1/70,000 the pressure of Earth's atmosphere at sea level. Triton was discovered by British astronomer William Lassell on October 10, 1846, just 17 days after the discovery of Neptune, he discovered Triton with 61 cm telescope. A brewer by trade, Lassell began making mirrors for his amateur telescope in 1820; when John Herschel received news of Neptune's discovery, he wrote to Lassell suggesting he search for possible moons. Lassell discovered Triton eight days later. Lassell claimed to have discovered rings. Although Neptune was confirmed to have rings, they are so faint and dark that it is doubtful that he saw them. Triton is named after the son of Poseidon; the name was first proposed by Camille Flammarion in his 1880 book Astronomie Populaire, was adopted many decades later.
Until the discovery of the second moon Nereid in 1949, Triton was referred to as "the satellite of Neptune". Lassell did not name his own discovery. Triton is unique among all large moons in the Solar System for its retrograde orbit around its planet. Most of the outer irregular moons of Jupiter and Saturn have retrograde orbits, as do some of Uranus's outer moons. However, these moons are all much more distant from their primaries, are small in comparison. Triton's orbit is associated with two tilts, the obliquity of Neptune's spin to Neptune's orbit, 30°, the inclination of Triton's orbit to Neptune's spin, 157°. Triton's orbit precesses forward relative to Neptune's spin with a period of about 678 Earth years, making its Neptune-orbit-relative inclination vary between 127° and 180° and in the past, to 173°; that inclination is 130°. Triton's rotation is tidally locked to be synchronous with its orbit around Neptune: it keeps one face oriented toward the planet at all times, its equator is exactly aligned with its orbital plane.
At the present time, Triton's rotational axis is about 40° from Neptune's orbital plane, hence at some point during Neptune's year each pole points close to the Sun like the poles of Uranus. As Neptune orbits the Sun, Triton's polar regions take turns facing the Sun, resulting in seasonal changes as one pole the other, moves into the sunlight; such changes were observed in 2010. Triton's revolution around Neptune has become a nearly perfect circle with an eccentricity of zero. Viscoelastic damping from tides alone is not thought to be capable of circularizing Triton's orbit in the time since the origin of the system, gas drag from a prograde debris disc is to have played a substantial role. Tidal interactions cause Triton's orbit, closer to Neptune than the Moon's is to Earth, to decay further; this will result in either a collision with Neptune's atmosphere or the breakup of Triton, forming a new ring system similar to that found around Saturn. Moons in retrograde orbits cannot form in the same region of the solar nebula as the planets they orbit, so Triton must have been captured from elsewhere.
It might therefore have originated in the Kuiper belt, a ring of small icy objects extending from just inside the orbit of Neptune to about 50 AU from the Sun. Thought to be the point of origin for the majority of short-period comets observed from Earth, the belt is home to several large, planet-like bodies including Pluto, now recognized as the largest in a population of Kuiper belt objects locked in orbital step with Neptune. Triton is only larger than Pluto and nearly identical in composition, which has led to the hypothesis that the two share a common origin; the proposed capture of Triton may explain several features of the Neptunian system, including the eccentric orbit of Neptune's moon Nereid and the scarcity of moons as compar
Density
The density, or more the volumetric mass density, of a substance is its mass per unit volume. The symbol most used for density is ρ, although the Latin letter D can be used. Mathematically, density is defined as mass divided by volume: ρ = m V where ρ is the density, m is the mass, V is the volume. In some cases, density is loosely defined as its weight per unit volume, although this is scientifically inaccurate – this quantity is more called specific weight. For a pure substance the density has the same numerical value as its mass concentration. Different materials have different densities, density may be relevant to buoyancy and packaging. Osmium and iridium are the densest known elements at standard conditions for temperature and pressure but certain chemical compounds may be denser. To simplify comparisons of density across different systems of units, it is sometimes replaced by the dimensionless quantity "relative density" or "specific gravity", i.e. the ratio of the density of the material to that of a standard material water.
Thus a relative density less than one means. The density of a material varies with pressure; this variation is small for solids and liquids but much greater for gases. Increasing the pressure on an object decreases the volume of the object and thus increases its density. Increasing the temperature of a substance decreases its density by increasing its volume. In most materials, heating the bottom of a fluid results in convection of the heat from the bottom to the top, due to the decrease in the density of the heated fluid; this causes it to rise relative to more dense unheated material. The reciprocal of the density of a substance is called its specific volume, a term sometimes used in thermodynamics. Density is an intensive property in that increasing the amount of a substance does not increase its density. In a well-known but apocryphal tale, Archimedes was given the task of determining whether King Hiero's goldsmith was embezzling gold during the manufacture of a golden wreath dedicated to the gods and replacing it with another, cheaper alloy.
Archimedes knew that the irregularly shaped wreath could be crushed into a cube whose volume could be calculated and compared with the mass. Baffled, Archimedes is said to have taken an immersion bath and observed from the rise of the water upon entering that he could calculate the volume of the gold wreath through the displacement of the water. Upon this discovery, he leapt from his bath and ran naked through the streets shouting, "Eureka! Eureka!". As a result, the term "eureka" entered common parlance and is used today to indicate a moment of enlightenment; the story first appeared in written form in Vitruvius' books of architecture, two centuries after it took place. Some scholars have doubted the accuracy of this tale, saying among other things that the method would have required precise measurements that would have been difficult to make at the time. From the equation for density, mass density has units of mass divided by volume; as there are many units of mass and volume covering many different magnitudes there are a large number of units for mass density in use.
The SI unit of kilogram per cubic metre and the cgs unit of gram per cubic centimetre are the most used units for density. One g/cm3 is equal to one thousand kg/m3. One cubic centimetre is equal to one millilitre. In industry, other larger or smaller units of mass and or volume are more practical and US customary units may be used. See below for a list of some of the most common units of density. A number of techniques as well as standards exist for the measurement of density of materials; such techniques include the use of a hydrometer, Hydrostatic balance, immersed body method, air comparison pycnometer, oscillating densitometer, as well as pour and tap. However, each individual method or technique measures different types of density, therefore it is necessary to have an understanding of the type of density being measured as well as the type of material in question; the density at all points of a homogeneous object equals its total mass divided by its total volume. The mass is measured with a scale or balance.
To determine the density of a liquid or a gas, a hydrometer, a dasymeter or a Coriolis flow meter may be used, respectively. Hydrostatic weighing uses the displacement of water due to a submerged object to determine the density of the object. If the body is not homogeneous its density varies between different regions of the object. In that case the density around any given location is determined by calculating the density of a small volume around that location. In the limit of an infinitesimal volume the density of an inhomogeneous object at a point becomes: ρ = d m / d V, where d V is an elementary volume at position r; the mass of the body t
