Vijay Shankar Sharma
Textbook physics terms. Not a BFUT reinterpretation. 371 terms. Textbook meanings only.
371 terms. Page 4 of 8.
nuclear · intro
The second lightest and second most abundant element in the universe, with an atomic nucleus containing two protons. Most of the helium in the universe was formed within the first few minutes after the hot early phase of cosmic expansion, during a process called primordial nucleosynthesis, with additional helium continuously produced by nuclear fusion inside stars. Helium is chemically inert and remains a gas at all but the most extreme low temperatures.
waves · intro
The SI unit of frequency, defined as one cycle per second, used to measure how often a repeating event, such as a wave oscillation or a rotating object, occurs. Named after German physicist Heinrich Hertz, who first demonstrated the existence of radio waves, the unit applies to phenomena as varied as sound pitch, alternating current, computer processor speeds, and the vibration frequency of atoms.
particle · intermediate
An elementary particle discovered at the Large Hadron Collider in 2012, associated with the Higgs field, which permeates all of space and gives fundamental particles their mass through their interaction with it. Particles that interact strongly with the Higgs field, such as the top quark, are heavy, while particles like the photon, which do not interact with it, remain massless. The discovery confirmed a key prediction of the Standard Model made decades earlier.
particle · intermediate
A quantum field that is theorized to permeate all of space uniformly, proposed in the 1960s and confirmed experimentally through the discovery of its associated particle, the Higgs boson, in 2012. Elementary particles acquire mass through their interaction with the Higgs field: particles that interact strongly with the field, such as the top quark, become heavy, while particles that do not interact with it, such as the photon, remain massless.
optics · intermediate
A technique for recording and later reconstructing the full three-dimensional light field of a scene, capturing both the intensity and phase information of light waves using interference patterns, typically created with coherent laser light. Unlike an ordinary photograph, a hologram appears to shift in perspective as the viewer moves around it, recreating a genuine sense of depth. Holography has applications in security, data storage, and imaging.
mechanics · intro
A law of elasticity stating that the force needed to stretch or compress a spring or elastic material by a given distance is directly proportional to that distance, at least within the material's elastic limit. Formulated by English scientist Robert Hooke, it is written as force equals a spring constant multiplied by displacement, and it describes the behavior of many elastic systems, from mechanical springs to the vibrations of atoms in a solid.
cosmology · intro
A number that describes the current rate at which the universe is expanding, expressing how fast a galaxy appears to recede from us for every unit of distance separating it from us, typically expressed in kilometers per second per megaparsec. First estimated by Edwin Hubble in 1929, its precise present-day value remains a subject of active research, since different measurement methods currently yield slightly different results.
cosmology · intermediate
A persistent discrepancy between two independent methods of measuring the Hubble constant: one based on direct, local distance measurements to nearby stars and supernovae, and another based on modeling the cosmic microwave background and the early universe within the standard Lambda-CDM cosmological model. The two approaches consistently yield different values for the expansion rate, a disagreement that has grown more statistically significant as measurement precision has improved, and its resolution remains an active area of cosmological research.
nuclear · intro
The lightest and most abundant element in the universe, with a nucleus normally consisting of a single proton. Hydrogen makes up roughly three-quarters of all ordinary matter by mass and is the primary fuel for nuclear fusion in stars, including the Sun. It exists in several isotopic forms, including deuterium and tritium, and plays a central role in astrophysics, chemistry, and energy research.
mechanics · intro
The pressure exerted by a fluid at rest due to the weight of the fluid above a given point, increasing with depth. It explains why water pressure increases as a diver descends and why dams must be built thicker at the base to withstand greater pressure near the bottom. Hydrostatic pressure depends on the fluid's density, the local gravitational acceleration, and the depth below the fluid's surface.
thermo · intro
An equation of state that relates the pressure, volume, temperature, and amount of an idealized gas, combining Boyle's law, Charles's law, and Avogadro's principle into a single expression. It assumes gas particles have negligible volume and no interactions except during perfectly elastic collisions. While no real gas behaves perfectly ideally, the ideal gas law provides an excellent approximation for many gases under normal temperature and pressure conditions.
mechanics · intro
The change in an object's momentum produced by a force acting over a period of time, calculated as the force multiplied by the time interval during which it acts, or equivalently as the area under a force-versus-time graph. Impulse explains why extending the time of a collision, such as with airbags or padded flooring, reduces the peak force experienced, since the same change in momentum is spread over a longer time.
mechanics · intro
A flat surface set at an angle to the horizontal, used as a simple machine to reduce the force needed to raise an object to a given height at the cost of moving it a longer distance. Ramps, wedges, and screws are all variations on the inclined plane principle. Analyzing motion on an inclined plane requires resolving gravity into components parallel and perpendicular to the sloped surface.
mechanics · intro
A collision between two or more objects in which total momentum is conserved but total kinetic energy is not, with some kinetic energy converted into other forms such as heat, sound, or permanent deformation. A perfectly inelastic collision is the extreme case where the colliding objects stick together and move with a common velocity afterward. Most real-world collisions, from car crashes to a ball of clay hitting the floor, are inelastic to some degree.
mechanics · intro
The tendency of an object to resist changes in its state of motion, whether at rest or moving at constant velocity, as described by Newton's first law of motion. An object's inertia is directly related to its mass; more massive objects require a larger force to achieve the same acceleration. Inertia explains why passengers in a car lurch forward when the car suddenly brakes, since their bodies tend to continue moving at the original speed.
mechanics · intermediate
A frame of reference in which an object with no net force acting on it moves at constant velocity, neither accelerating nor decelerating, consistent with Newton's first law. A frame that is itself accelerating or rotating, such as a spinning carousel, is a non-inertial frame, in which apparent forces like the Coriolis effect must be introduced to explain motion. Special relativity is built around the physics observed in inertial frames.
cosmology · intermediate
Also called: cosmic inflation
A theorized period of extremely rapid, exponential expansion of space that is proposed to have occurred a tiny fraction of a second into the universe's earliest history, before the standard hot expansion phase, within the framework of Lambda-CDM cosmology. Inflation was proposed to explain several observed features of the universe, including its large-scale flatness, uniform temperature, and the specific pattern of tiny density fluctuations that later seeded the formation of galaxies.
em · intro
Electromagnetic radiation with wavelengths longer than visible light but shorter than microwaves, commonly associated with heat, since most objects at room temperature emit strongly in the infrared. Infrared cameras detect this radiation to create thermal images even in complete darkness, and infrared light is used in remote controls, fiber-optic communication, and astronomical observations of dust-obscured regions of space.
em · intro
A material that strongly resists the flow of electric charge, or in a different context, heat, because it has very few charge carriers free to move within it. Materials like rubber, glass, and most plastics are good electrical insulators, used to coat wires and prevent unwanted current flow or electric shock. Thermal insulators, such as foam or wool, slow the transfer of heat by conduction.
cosmology · intermediate
Also called: ISW effect
A secondary effect that produces small additional temperature fluctuations in the cosmic microwave background, caused by photons gaining or losing energy as they pass through evolving gravitational potential wells, such as large cosmic voids or superclusters, during the universe's dark-energy-dominated expansion phase. Detecting this effect provides independent evidence for the presence of dark energy, since the effect would not occur in a universe where cosmic structures remained static over time.
waves · intro
The phenomenon that occurs when two or more waves overlap in the same region of space, combining according to the principle of superposition to produce a resulting wave that can be larger, smaller, or equal to the individual waves, depending on their relative phase. Constructive interference occurs when waves reinforce each other, while destructive interference occurs when they partially or fully cancel. Interference is a defining signature of wave behavior.
thermo · intermediate
The total energy contained within a system due to the microscopic kinetic and potential energy of its constituent particles, including molecular motion, vibrations, and intermolecular forces, but excluding the system's overall kinetic and potential energy as a whole object. Internal energy changes when heat is added or removed, or when work is done on or by the system, as described by the first law of thermodynamics.
mechanics · intro
A mathematical relationship in which a physical quantity's intensity or strength decreases in proportion to the square of the distance from its source. Gravity, electric fields, and the intensity of light and sound all follow inverse-square laws in idealized point-source situations, meaning doubling the distance from a source reduces the effect to one quarter of its original strength. This pattern arises naturally because the influence spreads out over the surface of an expanding sphere.
quantum · intro
An atom or molecule that has gained or lost one or more electrons, giving it a net positive or negative electric charge. Atoms that lose electrons become positively charged cations, while atoms that gain electrons become negatively charged anions. Ions are essential to chemistry, biology, and physics, playing roles ranging from nerve signal transmission in the body to the behavior of plasmas in stars and fluorescent lights.
quantum · intermediate
The minimum energy required to remove an electron from an atom or molecule in its gaseous state, converting it into a positively charged ion. Ionization energy generally increases across a row of the periodic table and decreases down a column, reflecting how tightly outer electrons are bound to the nucleus. High-energy radiation capable of ionizing atoms, such as ultraviolet light and X-rays, is called ionizing radiation and can damage biological tissue.
nuclear · intro
One of two or more forms of the same chemical element whose atoms have the same number of protons but different numbers of neutrons, giving them different atomic masses while retaining nearly identical chemical properties. Some isotopes are stable indefinitely, while others are radioactive and decay over time at a characteristic rate. Carbon-12 and carbon-14 are isotopes of carbon, differing only in their number of neutrons.
mechanics · intro
The SI unit of energy, work, and heat, defined as the energy transferred when a force of one newton acts over a distance of one meter. Named after English physicist James Prescott Joule, who demonstrated the equivalence of mechanical work and heat in the nineteenth century. A joule is a relatively small amount of energy in everyday terms; lifting a small apple about one meter against gravity requires roughly one joule.
particle · intermediate
A type of meson, a hadron made of one quark and one antiquark, containing a strange quark or antiquark paired with an up or down quark or antiquark. Kaons played a historically important role in particle physics, including the discovery of the phenomenon known as CP violation, a small asymmetry between matter and antimatter behavior. They are unstable and decay quickly into lighter particles.
thermo · intro
An absolute temperature scale used throughout science, in which zero kelvin corresponds to absolute zero, the theoretical lowest possible temperature, and each degree, called a kelvin, is the same size as a degree Celsius. Unlike Celsius or Fahrenheit, the Kelvin scale has no negative values under normal physical conditions, which makes it especially convenient for equations in thermodynamics and gas laws where temperature must be expressed relative to absolute zero.
mechanics · intro
Three laws describing planetary motion, formulated by Johannes Kepler in the early seventeenth century from careful astronomical observations. The first law states that planets orbit the Sun in ellipses with the Sun at one focus; the second states that a planet sweeps out equal areas in equal times, moving faster when closer to the Sun; and the third relates a planet's orbital period to its average distance from the Sun. Newton later showed these laws follow from his law of gravitation.
mechanics · intro
The branch of mechanics that describes the motion of objects, including their position, velocity, and acceleration, without considering the forces that cause that motion. Kinematic equations relate displacement, initial and final velocity, acceleration, and time for objects moving with constant acceleration, such as objects in free fall. Kinematics is contrasted with dynamics, which incorporates the forces responsible for the observed motion.
mechanics · intro
The energy an object possesses because of its motion, calculated for an everyday object as one half its mass multiplied by the square of its velocity. Kinetic energy increases rapidly with speed, since it depends on velocity squared, which is why a small increase in speed significantly raises the energy involved in a collision. It converts to and from other energy forms, such as potential energy, as an object speeds up or slows down.
thermo · intermediate
A model that explains the macroscopic properties of gases, such as pressure and temperature, in terms of the microscopic motion of their constituent particles, treating gas molecules as small particles in constant, random motion that collide elastically with each other and their container's walls. Kinetic theory successfully derives the ideal gas law and explains temperature as a measure of the average kinetic energy of gas particles.
em · intermediate
Two fundamental rules used to analyze electrical circuits, developed by Gustav Kirchhoff. The current law states that the total current flowing into a junction in a circuit must equal the total current flowing out, reflecting conservation of charge. The voltage law states that the sum of voltage changes around any closed loop in a circuit must equal zero, reflecting conservation of energy. Together they allow calculation of current and voltage throughout complex circuits.
particle · intermediate
An empirical mathematical relationship, discovered by physicist Yoshio Koide in 1981, that relates the measured masses of the three charged leptons, the electron, muon, and tau, through a specific formula that yields a value extremely close to two-thirds when applied to their experimentally measured masses. The formula's striking numerical accuracy has never been derived from first principles within the Standard Model of particle physics, and whether it reflects a deeper underlying physical principle or is simply a numerical coincidence remains an open question.
mechanics · intermediate
A reformulation of classical mechanics, developed by Joseph-Louis Lagrange, that describes motion using a single function called the Lagrangian, typically the difference between a system's kinetic and potential energy, combined with the principle of least action. Rather than analyzing forces directly, Lagrangian mechanics derives equations of motion from energy considerations, which often simplifies problems involving constraints or complex coordinate systems and extends naturally into quantum field theory.
optics · intro
A device that produces a highly focused, coherent beam of light through a process called stimulated emission, in which excited atoms or molecules are triggered to emit photons of the same wavelength, phase, and direction. The name is an acronym for light amplification by stimulated emission of radiation. Lasers are used across an enormous range of applications, including surgery, telecommunications, industrial cutting, and precision measurement.
thermo · intro
The amount of heat absorbed or released by a substance during a phase change, such as melting, freezing, boiling, or condensing, without any accompanying change in temperature. For example, converting one kilogram of ice at zero degrees Celsius into water at the same temperature requires a specific, fixed amount of energy known as the latent heat of fusion. Latent heat reflects the energy needed to rearrange molecular bonds rather than to increase molecular motion.
relativity · intermediate
A consequence of special relativity in which an object's measured length along its direction of motion appears shorter to an observer when the object moves at a significant fraction of the speed of light, relative to that observer. The effect only becomes noticeable at speeds approaching the speed of light and is symmetric: each observer sees the other's objects as contracted. Length contraction is closely related to time dilation.
optics · intro
A transparent optical component, typically made of glass or plastic, with at least one curved surface, that bends light rays through refraction to converge or diverge them. Convex lenses converge parallel light rays to a focal point and are used to magnify images or correct farsightedness, while concave lenses spread light rays apart and are used to correct nearsightedness. Lenses form the basis of eyeglasses, cameras, microscopes, and telescopes.
em · intermediate
A law stating that the direction of an electric current induced by a changing magnetic field always opposes the change that produced it, a consequence of the conservation of energy. Lenz's law explains why moving a magnet toward a coil induces a current that creates a magnetic field opposing the magnet's approach, effectively resisting the motion. It provides the direction that complements the magnitude given by Faraday's law of induction.
particle · intermediate
A category of fundamental particle that does not experience the strong nuclear force, including the electron, muon, tau, and their associated neutrinos, along with their antiparticles. Leptons are considered elementary, with no known internal substructure, and are classified as fermions. The electron is the only lepton stable enough to exist as ordinary matter under normal conditions; the others are far more massive and decay quickly.
mechanics · intro
The upward force generated on an object, such as an aircraft wing, as it moves through a fluid, arising from a pressure difference between the upper and lower surfaces caused by the object's shape and angle relative to the airflow. Lift allows heavier-than-air vehicles to fly by counteracting gravity, and its magnitude depends on the object's speed, shape, surface area, and the density of the surrounding air.
astro · intro
A unit of distance, rather than time, equal to the distance light travels in one year through the vacuum of space, approximately 9.46 trillion kilometers. Astronomers use light-years to describe the vast distances between stars and galaxies, since more familiar units like kilometers become unwieldy at cosmic scales. Because light takes time to travel, observing an object a certain number of light-years away also means seeing it as it appeared that many years in the past.
cosmology · intermediate
A persistent discrepancy in cosmology between the predicted abundance of lithium-7 from standard Big Bang nucleosynthesis calculations and the actual amount of lithium-7 observed in the atmospheres of old, metal-poor stars, which is consistently measured to be roughly three times lower than predicted. Despite decades of study, no fully satisfying explanation for this discrepancy within the standard cosmological model has been universally accepted, though various astrophysical and nuclear physics explanations have been proposed.
waves · intro
A wave in which the oscillation of the medium occurs parallel to the direction the wave travels, creating alternating regions of compression and rarefaction. Sound waves in air are the most common example of longitudinal waves, as air molecules vibrate back and forth along the same direction the sound travels. This contrasts with transverse waves, such as light or a wave on a string, where the oscillation is perpendicular to the direction of travel.
em · intermediate
The combined electric and magnetic force experienced by a charged particle moving through electric and magnetic fields, calculated as the charge multiplied by the electric field plus the charge times the particle's velocity crossed with the magnetic field. The magnetic component of the Lorentz force acts perpendicular to both the particle's velocity and the magnetic field, causing charged particles to move in curved or helical paths within a magnetic field.
relativity · intermediate
A set of equations from special relativity that relate the coordinates of space and time as measured by two observers moving at constant velocity relative to each other. Unlike the simple addition of velocities used in classical Newtonian physics, Lorentz transformations account for the fact that the speed of light remains constant for all observers, leading to effects such as time dilation and length contraction at high relative speeds.
astro · intro
The total amount of energy a star or other astronomical object emits per unit time, an intrinsic property independent of the observer's distance from the object, usually expressed in watts or in multiples of the Sun's luminosity. Luminosity depends on both an object's surface temperature and its surface area, so a large, cool star can be more luminous than a small, hot one. It is distinguished from apparent brightness, which also depends on distance.
cosmology · intermediate
A method of expressing the distance to an astronomical object, calculated by comparing the object's known intrinsic luminosity to its observed apparent brightness, accounting for how radiation spreads out and, at cosmological distances, how the expansion of the universe dims and stretches the light along its path. Luminosity distance differs from simple geometric distance for very distant objects, since it must account for the universe's expansion history, making it a valuable tool for testing cosmological models using standard candles such as Type Ia supernovae.