Vijay Shankar Sharma
Textbook physics terms. Not a BFUT reinterpretation. 371 terms. Textbook meanings only.
371 terms. Page 1 of 8.
astro · intro
A measure of the intrinsic brightness of a celestial object, defined as the apparent magnitude it would have if placed at a standard distance of 10 parsecs from the observer, removing the effect of actual distance. Because it reflects true luminosity rather than observed brightness, absolute magnitude allows astronomers to directly compare the brightness of stars located at very different distances from Earth.
thermo · intro
Also called: 0 kelvin
The lowest possible temperature, defined as 0 kelvin or -273.15 degrees Celsius. At this point a system has the minimum thermal energy allowed by quantum mechanics, since some zero-point motion always remains. No physical process has ever reached it exactly, though laboratories have cooled small samples to within a billionth of a degree using laser and magnetic trapping techniques. It serves as the reference point for the Kelvin temperature scale.
mechanics · intro
The rate at which an object's velocity changes over time, measured in meters per second squared. It is a vector, so it captures both speeding up, slowing down, and changing direction. A falling object near Earth's surface accelerates at roughly 9.8 meters per second squared due to gravity. Newton's second law ties acceleration directly to the net force acting on an object and its mass.
cosmology · intermediate
Also called: acoustic peaks
A series of characteristic bumps visible in the power spectrum of temperature fluctuations across the cosmic microwave background, produced by sound waves that propagated through the hot, dense plasma of the early universe before neutral atoms formed. The precise pattern, spacing, and relative heights of these acoustic peaks encode detailed information about the universe's geometry, composition, and the relative amounts of ordinary matter, dark matter, and dark energy.
mechanics · intermediate
Also called: least action
A quantity that combines a system's energy and time, or momentum and position, into a single number with units of energy multiplied by time. The principle of least action states that a physical system evolves along the path that makes this quantity stationary, usually a minimum. This idea underlies Lagrangian mechanics and extends into quantum theory, where the smallest meaningful unit of action is set by Planck's constant.
thermo · intermediate
A thermodynamic process in which a system exchanges no heat with its surroundings, so any change in internal energy comes entirely from work done on or by the system. Compressing gas quickly in an insulated cylinder is a common example, since there is no time for heat to escape. Adiabatic processes appear throughout thermodynamics, from engine cycles to the cooling of rising air parcels in the atmosphere.
nuclear · intro
A type of radioactive decay in which an unstable atomic nucleus emits an alpha particle, made of two protons and two neutrons bound together and identical to a helium-4 nucleus. This reduces the parent nucleus's atomic number by two and its mass number by four. Alpha decay is common in heavy elements like uranium and radium, and the emitted particles are stopped easily by a sheet of paper or a few centimeters of air.
nuclear · intro
Also called: helium nucleus
A particle made of two protons and two neutrons bound together, identical in structure to the nucleus of a helium-4 atom. Alpha particles carry a positive charge of plus two and are relatively heavy and slow compared to other radiation types, which makes them easy to stop with a sheet of paper. They are commonly emitted during the radioactive decay of heavy elements such as uranium.
em · intro
Also called: amp
The SI base unit of electric current, defined by fixing the numerical value of the elementary charge. One ampere corresponds to a flow of about 6.24 times ten to the eighteenth electrons per second past a given point in a conductor. It is named after French physicist Andre-Marie Ampere, an early investigator of the relationship between electricity and magnetism.
waves · intro
The maximum displacement or intensity of a wave or oscillation, measured from its equilibrium or rest position. For a sound wave, larger amplitude corresponds to louder sound; for a light wave, it relates to brightness. Amplitude is distinct from frequency, which describes how often the oscillation repeats. In simple harmonic motion, amplitude stays constant unless energy is added or removed from the system.
mechanics · intermediate
A measure of an object's rotational motion, calculated from its moment of inertia and angular velocity for a rotating body, or from its mass, velocity, and distance from a chosen point for an orbiting one. Angular momentum is conserved in any system with no external torque, which is why a spinning figure skater speeds up when pulling in their arms. It plays a central role in orbital mechanics and atomic structure.
mechanics · intro
The rate at which an object rotates or revolves around an axis, expressed in radians per second. It describes how quickly the angle of rotation changes with time, independent of the object's size. A point farther from the rotation axis moves faster in a straight-line sense but has the same angular velocity as a point closer in, since both sweep through the same angle in the same time.
particle · intermediate
The process in which a particle and its corresponding antiparticle meet and convert entirely into energy, typically in the form of photons, according to Einstein's mass-energy relation. For example, an electron and a positron annihilate to produce two gamma-ray photons. Annihilation is the reverse of pair production, in which energy converts into a particle-antiparticle pair, and both processes conserve total energy, momentum, and charge.
particle · intro
Matter composed of antiparticles, which have the same mass as their ordinary-matter counterparts but opposite electric charge and other quantum properties. The positron, for instance, is the antimatter counterpart of the electron. When matter and antimatter meet, they annihilate each other and release energy. Antimatter is rare in the observable universe, and explaining this imbalance between matter and antimatter is an open problem in particle physics and cosmology.
particle · intro
A particle that has the same mass as its ordinary counterpart but opposite values for properties like electric charge. Every known particle has a corresponding antiparticle; the electron's antiparticle is the positron, and the proton's is the antiproton. Some particles, like the photon, are their own antiparticle. When a particle meets its antiparticle, the pair typically annihilates into energy.
optics · intro
The opening in an optical system, such as a camera lens or telescope, through which light passes. A larger aperture lets in more light and improves resolution but reduces depth of field in imaging systems. Aperture size is often expressed as an f-number, the ratio of focal length to aperture diameter, and it directly affects both the brightness and sharpness of the resulting image.
astro · intro
A measure of how bright a celestial object appears from Earth, on a logarithmic scale where lower and negative numbers indicate brighter objects. It depends on both the object's true luminosity and its distance, so a nearby faint star can appear brighter than a distant powerful one. Apparent magnitude is distinguished from absolute magnitude, which measures intrinsic brightness at a standard reference distance.
mechanics · intro
The principle stating that an object submerged, wholly or partly, in a fluid experiences an upward buoyant force equal to the weight of the fluid it displaces. This explains why objects denser than water sink while less dense ones float, and why a ship made of steel can float if its overall shape displaces enough water. It was first described by the ancient Greek mathematician Archimedes.
astro · intermediate
A narrow, high-speed beam of ionized matter ejected from the vicinity of a compact object, such as a black hole, neutron star, or young star, typically launched along the object's rotation axis. Jets from supermassive black holes at the centers of active galaxies can extend for millions of light-years and are powered by the intense gravitational and magnetic energy near the central object. Their exact launching mechanism remains an active area of astrophysical research.
nuclear · intro
The basic building block of ordinary matter, consisting of a dense central nucleus made of protons and neutrons, surrounded by a cloud of electrons held in place by electromagnetic attraction. The number of protons defines which chemical element an atom belongs to. Atoms are extremely small, roughly a tenth of a nanometer across, yet almost all of their mass is concentrated in the nucleus.
nuclear · intro
The total mass of an atom, expressed in atomic mass units, where one unit is defined as one-twelfth the mass of a carbon-12 atom. It is determined mainly by the combined number of protons and neutrons in the nucleus, since electrons contribute very little mass. The atomic mass listed on a periodic table is usually a weighted average across an element's naturally occurring isotopes.
nuclear · intro
The number of protons in an atom's nucleus, which determines which chemical element the atom is. It is denoted by the symbol Z and defines an element's position on the periodic table. Atoms of the same element always share the same atomic number, even though they can have different numbers of neutrons, a variation known as isotopes.
waves · intermediate
The gradual loss of intensity of a wave, signal, or beam of particles as it travels through a medium, caused by absorption, scattering, or spreading. Light attenuates as it passes through fog or water, and radio signals attenuate with distance and obstacles. Attenuation is often described by an exponential decay law and is a key factor in designing communication systems and radiation shielding.
thermo · intro
Also called: Avogadro's number
The number of elementary units, such as atoms or molecules, in one mole of a substance, approximately 6.022 times ten to the twenty-third per mole. It links the microscopic scale of individual atoms to the macroscopic scale of measurable quantities like grams and liters. The constant is named after Italian scientist Amedeo Avogadro, though he did not calculate its exact value himself.
quantum · intermediate
The range of energy levels in a solid material where no electron states can exist, lying between the valence band, which is normally filled with electrons, and the conduction band, where electrons can move freely and conduct electricity. The size of the band gap determines whether a material behaves as an insulator, semiconductor, or conductor. Semiconductors like silicon have a moderate band gap, exploited in transistors and solar cells.
waves · intermediate
The range of frequencies contained within a signal or that a system can transmit or process effectively, usually expressed in hertz. A wider bandwidth allows more information to be carried per unit time, which is why higher-bandwidth channels support faster data transmission. The concept applies broadly, from radio communication to the frequency range a wave packet spans in quantum mechanics.
particle · intermediate
A category of subatomic particle made of three quarks bound together by the strong force. Protons and neutrons, the particles that make up atomic nuclei, are the most familiar baryons. Baryons belong to a broader family called hadrons, and every baryon has a corresponding antibaryon made of three antiquarks. The total number of baryons minus antibaryons, called baryon number, is conserved in essentially all known particle interactions.
cosmology · intermediate
Also called: BAO
A subtle, regular pattern in the large-scale distribution of galaxies throughout the universe, left behind as a fossil imprint of the same sound waves that produced the acoustic peaks seen in the cosmic microwave background. This pattern provides a standard ruler, a distance scale of known physical size, that astronomers use to measure cosmic distances and track the universe's expansion history across billions of years.
waves · intro
The periodic variation in amplitude heard when two sound waves of slightly different frequencies overlap, produced by their alternating constructive and destructive interference. The beat frequency equals the difference between the two original frequencies. Musicians use beats to tune instruments, listening for the beating to slow and disappear as two notes are brought into exact agreement.
nuclear · intro
A type of radioactive decay in which a neutron in an atomic nucleus converts into a proton, or a proton converts into a neutron, emitting an electron or positron along with a neutrino or antineutrino. This process changes the atomic number of the nucleus by one while leaving the mass number unchanged, effectively transforming the atom into a different element. Beta decay is driven by the weak nuclear force.
cosmology · intro
The standard cosmological model describing the early universe as an extremely hot, dense state that has been expanding and cooling ever since. It is supported by several independent lines of evidence, including the cosmic microwave background radiation, the observed abundances of light elements, and the recession of distant galaxies. The Big Bang describes the expansion history of the observable universe rather than an explosion into pre-existing space.
astro · intro
A system of two stars gravitationally bound together, orbiting a common center of mass. Binary stars are common in the galaxy, and studying their orbits allows astronomers to measure stellar masses directly, since the orbital period and separation depend on the combined mass of the pair through Kepler's laws. Some binaries eventually interact through mass transfer, sometimes ending in dramatic events like a nova or supernova.
nuclear · intermediate
The energy required to completely separate the components of a bound system, such as the protons and neutrons in an atomic nucleus, or an electron orbiting an atom. A higher binding energy means the system is more stable, since more energy would need to be supplied to break it apart. Nuclear binding energy is the source of the enormous energy released in nuclear fission and fusion reactions.
relativity · intro
A region of spacetime where gravity is so strong that nothing, not even light, can escape once it crosses the boundary known as the event horizon. Black holes form when massive stars collapse at the end of their lives, or through the merger of smaller black holes and neutron stars. Their existence is confirmed through observations of orbiting stars, gravitational waves, and direct imaging of the shadow they cast.
thermo · intermediate
The electromagnetic radiation emitted by an idealized object, called a blackbody, that absorbs all radiation falling on it and re-emits energy based purely on its temperature. The spectrum of this radiation follows a characteristic curve described by Planck's law, with hotter objects emitting more strongly at shorter wavelengths. Blackbody radiation explains why heated metal glows red, then orange, then white as its temperature rises.
astro · intro
A shift of light or other electromagnetic radiation toward shorter, bluer wavelengths, caused by relative motion of the source toward the observer, or by a gravitational field decreasing along the light's path. It is the counterpart to redshift and follows the same Doppler and gravitational principles. Blueshift is observed, for example, in the light from stars orbiting close to the center of the galaxy.
quantum · intro
An early model of the atom, proposed by Niels Bohr in 1913, in which electrons orbit the nucleus only in specific allowed circular paths with fixed energy levels, rather than at arbitrary distances. Electrons emit or absorb light of specific wavelengths when jumping between these levels. Although superseded by the more complete quantum mechanical model of the atom, the Bohr model successfully predicted the spectral lines of hydrogen.
thermo · intermediate
A fundamental physical constant that relates the average kinetic energy of particles in a gas to its temperature, with a value of about 1.38 times ten to the minus twenty-three joules per kelvin. It bridges the microscopic world of individual particle motion and the macroscopic quantity we measure as temperature. The constant is named after Austrian physicist Ludwig Boltzmann, a founder of statistical mechanics.
quantum · intermediate
A foundational rule of quantum mechanics, proposed by physicist Max Born in 1926, stating that the probability of finding a quantum system in a particular state upon measurement is given by the square of the magnitude of the system's wavefunction at that state. The Born rule provides the crucial link between the abstract mathematical wavefunction, which itself has no direct physical interpretation, and the concrete, measurable probabilities of experimental outcomes.
particle · intermediate
A category of particle that follows Bose-Einstein statistics and can occupy the same quantum state as other identical bosons in unlimited numbers. Force-carrying particles such as photons, gluons, and the Higgs boson fall into this category, distinguishing them from matter particles called fermions, which cannot share a quantum state. Bosons generally have integer values of a quantum property called spin.
thermo · intro
A gas law stating that, at constant temperature, the pressure of a fixed amount of gas is inversely proportional to its volume: as volume decreases, pressure increases proportionally, and vice versa. Formulated by Robert Boyle in the seventeenth century, it is one of the earliest quantitative gas laws and forms part of the broader ideal gas law used throughout thermodynamics.
thermo · intro
The random, jittery movement of small particles suspended in a fluid, caused by countless collisions with the fluid's molecules. First observed in pollen grains by botanist Robert Brown, it was later explained theoretically by Albert Einstein as direct evidence for the existence of atoms and molecules. Brownian motion is a foundational example of a random walk process, used across physics, finance, and biology.
mechanics · intermediate
A measure of a material's resistance to uniform compression, defined as the ratio of an applied pressure change to the resulting fractional change in volume. Materials with a high bulk modulus, like steel, are difficult to compress, while gases have a much lower bulk modulus and compress easily. It is one of several elastic moduli used to describe how materials respond to stress.
mechanics · intro
The upward force exerted by a fluid on an object partly or fully submerged in it, arising because fluid pressure increases with depth. This force allows objects less dense than the surrounding fluid to float, and is quantified by Archimedes' principle. Buoyancy explains why a steel ship can float while a solid steel block sinks, since the ship's shape displaces a much larger volume of water.
thermo · intro
The experimental technique used to measure the amount of heat released or absorbed during a physical or chemical process, typically using an insulated device called a calorimeter. By tracking the temperature change of a known quantity of a substance, such as water, scientists can calculate the heat exchanged based on the substance's specific heat capacity. Calorimetry underlies measurements of reaction energies, specific heats, and latent heats across physics and chemistry.
em · intro
A measure of a component's ability to store electric charge for a given voltage applied across it, measured in farads. A capacitor with higher capacitance stores more charge at the same voltage. Capacitance depends on the geometry of the conductors involved and the insulating material, called a dielectric, between them; larger plate area and smaller separation both increase capacitance.
em · intro
An electronic component that stores electric energy in an electric field between two conductive plates separated by an insulator. When connected to a voltage source, charge accumulates on the plates until the capacitor reaches that voltage. Capacitors are used to smooth power supplies, store energy for quick release, and filter electronic signals, and their behavior is characterized by their capacitance.
nuclear · intro
Also called: radiocarbon dating
A method for estimating the age of organic material by measuring the remaining proportion of carbon-14, a radioactive isotope that decays at a known, steady rate with a half-life of about 5,730 years. Living organisms continuously exchange carbon with their environment, keeping carbon-14 levels roughly constant, but this exchange stops at death, after which the isotope steadily decays. Comparing remaining carbon-14 to stable carbon-12 gives an age estimate for samples up to roughly 50,000 years old.
thermo · intermediate
An idealized thermodynamic cycle that represents the most efficient possible heat engine operating between two temperatures, consisting of two isothermal and two adiabatic processes. No real engine can exceed the efficiency of a Carnot cycle operating between the same hot and cold reservoirs, making it a theoretical upper bound used to evaluate real engines. It was proposed by French engineer Sadi Carnot in 1824.
mechanics · intro
The point in a system of objects, or within a single object, where its mass can be considered to be concentrated for the purpose of analyzing motion. For a symmetric object of uniform density, the center of mass sits at its geometric center. Under gravity, an object behaves as though all its weight acts at this point, which simplifies the study of complex motions like a spinning wrench thrown through the air.