Vijay Shankar Sharma
Textbook physics terms. Not a BFUT reinterpretation. 371 terms. Textbook meanings only.
20 terms. Page 1 of 1.
waves · intro
The gradual reduction in the amplitude of an oscillation over time, usually caused by energy loss to friction, air resistance, or electrical resistance. A swinging pendulum in air eventually comes to rest due to damping, while a car's shock absorbers are specifically designed to add damping and smooth out bouncing after a bump. Systems can be underdamped, critically damped, or overdamped depending on how quickly oscillation is suppressed.
cosmology · intro
A mysterious form of energy that permeates all of space and is currently understood to be driving the accelerating expansion of the universe, first discovered through observations of distant Type Ia supernovae in the late 1990s. Within the standard Lambda-CDM cosmological model, dark energy is modeled as a cosmological constant and accounts for roughly 68 percent of the universe's total energy content, though its underlying physical nature remains one of the biggest open questions in modern physics.
cosmology · intro
A form of matter that does not emit, absorb, or reflect light, and has never been directly detected, but whose gravitational influence is inferred from its effects on visible matter, such as the rotation speeds of galaxies, the motion of galaxy clusters, and the pattern of fluctuations in the cosmic microwave background. Within the standard Lambda-CDM cosmological model, dark matter accounts for roughly 27 percent of the universe's total energy content, far outweighing ordinary visible matter.
quantum · intermediate
The wavelength associated with any moving particle, proposed by physicist Louis de Broglie in 1924, calculated by dividing Planck's constant by the particle's momentum. This idea extended the wave-particle duality already known for light to all matter, suggesting that electrons and even larger objects have an associated wave nature. The de Broglie wavelength of everyday objects is far too small to observe, but it becomes significant for electrons and other subatomic particles.
nuclear · intermediate
A value that characterizes how quickly a radioactive isotope decays, representing the probability per unit time that any given nucleus will decay. It is directly related to the isotope's half-life; a larger decay constant means faster decay and a shorter half-life. The decay constant appears in the exponential decay equation used to predict how much of a radioactive sample remains after a given time.
waves · intro
A logarithmic unit used to express the ratio between two values of power or intensity, most commonly used to measure the loudness of sound. Because human hearing spans an enormous range of intensities, the logarithmic decibel scale compresses this range into more manageable numbers; a 10 decibel increase corresponds to a tenfold increase in sound intensity. Normal conversation is roughly 60 decibels, while a jet engine can exceed 140 decibels.
astro · intermediate
A quantum mechanical pressure that arises because fermions, such as electrons or neutrons, cannot occupy the same quantum state, a restriction known as the Pauli exclusion principle. When matter is compressed to extremely high densities, this pressure resists further compression even at zero temperature. Degeneracy pressure supports white dwarf stars against gravitational collapse, and a related form supports neutron stars, until gravity overwhelms it in the most massive collapsing stars.
thermo · intermediate
The number of independent ways a system can store energy or the number of independent coordinates needed to fully describe its configuration. A single free particle moving in three dimensions has three translational degrees of freedom, while a diatomic gas molecule also has rotational and vibrational degrees of freedom. In statistical mechanics, each degree of freedom contributes a predictable share of a system's total thermal energy.
mechanics · intro
The amount of mass contained within a given volume of a substance, usually expressed in kilograms per cubic meter or grams per cubic centimeter. Density determines whether an object floats or sinks in a given fluid, and it varies with temperature and pressure for gases and, to a lesser extent, liquids and solids. Water has a density of about 1,000 kilograms per cubic meter, which serves as a common reference point.
waves · intro
The cancellation of waves that occurs when two or more waves overlap while out of phase, so that the crest of one wave aligns with the trough of another, reducing or eliminating the combined amplitude. It is one of the two basic outcomes of wave superposition, the other being constructive interference. Noise-cancelling headphones use destructive interference deliberately, generating a sound wave that cancels out unwanted ambient noise.
nuclear · intro
Also called: heavy hydrogen
An isotope of hydrogen whose nucleus contains one proton and one neutron, making it roughly twice as massive as ordinary hydrogen, which has no neutron. It occurs naturally in small quantities in ordinary water and is used in nuclear fusion research, certain nuclear reactors, and as a tracer in chemistry and biology. Its chemical symbol is often written as D or 2H.
em · intermediate
A weak form of magnetism exhibited by all materials, in which an external magnetic field induces a very slight magnetization that opposes the applied field, causing a small repulsive force. Diamagnetism is typically far weaker than paramagnetism or ferromagnetism and is only clearly observable in materials that lack these stronger effects, such as water, wood, and most organic compounds. It arises from changes in electron orbital motion in response to the applied field.
waves · intro
The bending and spreading of waves as they pass through a narrow opening or around an obstacle, most noticeable when the size of the opening or obstacle is comparable to the wavelength of the wave. Diffraction explains why sound can be heard around corners and why light passing through a narrow slit produces a pattern of bright and dark bands rather than a sharp shadow. It is a defining feature that distinguishes wave behavior from simple particle behavior.
optics · intermediate
An optical component consisting of a surface with many closely and regularly spaced parallel lines or slits, used to split and diffract light into its component wavelengths. Because each wavelength diffracts at a slightly different angle, a diffraction grating produces a spectrum similar to a prism, but with generally higher resolution. Diffraction gratings are widely used in spectrometers to analyze the composition of light from sources ranging from lab samples to distant stars.
thermo · intro
The gradual spreading out of particles, such as molecules of a gas or solute in a liquid, from regions of higher concentration to regions of lower concentration, driven by random molecular motion. Diffusion continues until concentration is uniform throughout the available space, and its rate depends on temperature, particle size, and the medium involved. The smell of perfume spreading through a room is a familiar everyday example of diffusion.
math-methods · intro
A technique in physics for checking the consistency of equations and estimating relationships between quantities by tracking the fundamental dimensions involved, such as length, mass, and time, rather than their numerical values. If an equation's terms do not have matching dimensions, the equation must be wrong. Dimensional analysis is often used as a quick sanity check on calculations and can also help derive the general form of physical relationships before detailed theory is developed.
em · intermediate
A pair of equal and opposite charges, or equivalent poles, separated by a small distance, which together create a characteristic field pattern in the surrounding space. An electric dipole consists of a positive and negative charge, common in polar molecules like water, while a magnetic dipole, such as a bar magnet, has a north and south pole. Dipoles interact with external fields, tending to align with them, and radiate energy when they oscillate.
em · intro
Also called: DC
An electric current that flows steadily in a single direction, as opposed to alternating current, which periodically reverses direction. Batteries and solar cells produce direct current naturally, and it is the form of electricity used internally by most electronic devices, even those plugged into an alternating current outlet, after passing through a rectifier. Direct current was central to Thomas Edison's early electrical power systems in the late nineteenth century.
optics · intermediate
The phenomenon in which the refractive index of a material, and therefore the angle at which light bends, varies with the wavelength of the light passing through it. Dispersion causes white light passing through a prism to spread out into its constituent colors, since different wavelengths refract by slightly different amounts. It is also responsible for the chromatic aberration seen in simple lenses and for the formation of rainbows in water droplets.
waves · intro
The change in observed frequency or wavelength of a wave caused by relative motion between the source and the observer. Sound from an approaching ambulance siren rises in pitch and drops as it passes and recedes, which is a familiar example. The same principle applies to light, where it produces the redshift and blueshift used by astronomers to measure the motion of stars, galaxies, and other celestial objects.