A mathematical model which seeks to describe
atomic nuclei by solving the non-relativistic
Schrödinger equation for all constituent
nucleons and the
forces that exist between them. Such methods yield precise results for very light nuclei but become more approximate for heavier nuclei.
In
optics and lens design, a measure of a transparent material's
dispersion (a variation of
refractive index versus
wavelength). High values of V indicate low dispersion.
In
electrochemistry, the electrode potential of a metal measured with respect to a universal reference system (without any additional metal–solution interface).
Any system of
measurement that begins at a minimum, or zero point, and progresses in only one direction. The zero point of an absolute scale is a natural minimum, leaving only one direction in which to progress, whereas an arbitrary or "relative" scale begins at some point selected by a person and can progress in both directions.
The theoretical lowest possible
temperature, understood by international agreement as equivalent to 0
Kelvin or −273.15 °C (−459.67 °F). More formally, it is the theoretical lower limit of the
thermodynamic temperature scale, at which
enthalpy and
entropy of a cooled
ideal gas reach their minimum values and the fundamental particles of nature have minimal vibrational motion.
The observation that the
expansion of the
universe is such that the velocity at which a distant galaxy is receding from the observer is continuously increasing with time.[1][2][3][4]
adhesion is what makes things stick together.
It's the force that allows tape to stick to a surface or glue to hold two objects together. Contrast cohesion.
A process which occurs without transfer of
heat or
mass of substances between a
thermodynamic system and its surroundings. In an adiabatic process, energy is transferred to the surroundings only as
work.[5][6] The adiabatic process provides a rigorous conceptual basis for the theory used to expound the
first law of thermodynamics, and as such it is a key concept in
thermodynamics.
The study of the motion of
air, particularly its interaction with a solid object, such as an
airplane wing. It is a sub-field of
fluid dynamics and
gas dynamics, and many aspects of aerodynamics theory are common to these fields.
An
optical system that produces no net convergence or divergence of the beam, i.e. has an infinite
effective focal length.[7] This type of system can be created with a pair of optical elements where the distance between the elements is equal to the sum of each element's
focal length ().
1. In
meteorology, a volume of
air that is defined by its
temperature and
water vapor content. Air masses may cover many hundreds or thousands of square miles and generally adapt to the characteristics of the surface below them. They are often classified according to their latitude and their source regions.
2. In
astronomy, the "amount of air that one is looking through"[8] when observing a star or other celestial source from a vantage point that is within
Earth's atmosphere. It is formulated as the integral of air density along the light
ray.
Defines the direct optical path length through the
Earth's atmosphere, expressed as a ratio relative to the path length vertically upwards, i.e. at the
zenith. The air mass coefficient can be used to help characterize the solar spectrum after
solar radiation has traveled through the atmosphere.
A type of
subatomic particle consisting of two
protons and two
neutrons bound together into a particle identical to the
nucleus of a
helium-4ion. It has a charge of +2
e and a mass of 4
u. Alpha particles are classically produced in the process of
radioactivealpha decay, but may also be produced in other ways and given the same name.
An electronic device that can increase the
power of a
signal (a time-varying
voltage or
current). It is a
two-port electronic circuit that uses electric power from a
power supply to increase the
amplitude of a signal applied to its input terminals, producing a proportionally greater amplitude signal at its output. The amount of amplification provided by an amplifier is measured by its
gain: the ratio of output voltage, current, or power to input. An amplifier is a circuit that has a
power gain greater than one.[9][10][11]
The change in direction of a
wavefront at an
interface between two different
media so that the wavefront returns into the medium from which it originated. Common examples include the reflection of
light,
sound, and
water waves. The law of reflection says that for
specular reflection the angle at which the wave is incident on the surface equals the angle at which it is reflected.
Mirrors exhibit specular reflection.
The time rate of change of
angular velocity. In three dimensions, it is a
pseudovector. In
SI units, it is measured in
radians per second squared (rad/s2), and is usually denoted by the Greek letter
alpha (α).[12] Just like angular velocity, there are two types of angular acceleration: spin angular acceleration and orbital angular acceleration, representing the time rate of change of spin angular velocity and orbital angular velocity, respectively. Unlike linear acceleration, angular acceleration need not be caused by a net external
torque. For example, a figure skater can speed up her rotation (thereby obtaining an angular acceleration) simply by contracting her arms inwards, which involves no external torque.
The angle (in
radians,
degrees, or
revolutions) through which a point revolving around a centre or line has been rotated in a specified sense about a specified
axis.
Also angular speed, radial frequency, circular frequency, orbital frequency, radian frequency, and pulsatance.
A scalar measure of rotation rate. It refers to the
angular displacement per unit time (e.g. in rotation) or the rate of change of the phase of a sinusoidal waveform (e.g. in oscillations and waves), or as the rate of change of the argument of the sine function. Angular frequency (or angular speed) is the magnitude of the vector quantity that is
angular velocity. The term angular frequency vector is sometimes used as a synonym for the vector quantity angular velocity.[13]
One
revolution is equal to 2π
radians, hence[13][14]
where:
ω is the angular frequency or angular speed (measured in
radians per second),
Also (rarely) moment of momentum or rotational momentum.
The rotational equivalent of
linear momentum. It is an important quantity in physics because it is a
conserved quantity–that is, the total angular momentum of a closed system remains constant.
How fast an object rotates or revolves relative to another point, i.e. how fast the angular position or orientation of an object changes with time. There are two types of angular velocity: orbital angular velocity and spin angular velocity. Spin angular velocity refers to how fast a rigid body rotates with respect to its centre of rotation. Orbital angular velocity refers to how fast a rigid body's centre of rotation revolves about a fixed origin, i.e. the time rate of change of its angular position relative to the origin. In general, angular velocity is measured in angle per unit time, e.g.
radians per second. The
SI unit of angular velocity is expressed as radians/sec with the radian having a dimensionless value of unity, thus the SI units of angular velocity are listed as 1/sec. Angular velocity is usually represented by the Greek letter
omega (ω, sometimes Ω). By convention, positive angular velocity indicates counter-clockwise rotation, while negative is clockwise.
In
particle physics, the process that occurs when a
subatomic particle collides with its respective
antiparticle to produce other particles, such as an
electron colliding with a
positron to produce two
photons.[15] The total
energy and
momentum of the initial pair are conserved in the process and distributed among a set of other particles in the final state. Antiparticles have exactly opposite additive
quantum numbers from particles, so the sums of all quantum numbers of such an original pair are zero. Hence, any set of particles may be produced whose total quantum numbers are also zero as long as
conservation of energy and
conservation of momentum are obeyed.[16]
The electrode through which a conventional
electric current flows into a polarized electrical device; the direction of current flow is, by convention, opposite to the direction of
electron flow, and so electrons flow out of the anode. In a
galvanic cell, the anode is the negative terminal or pole which emits electrons toward the external part of an
electrical circuit. However, in an
electrolytic cell, the anode is the wire or plate having excess positive charge, so named because negatively charged
anions tend to move towards it. Contrast cathode.
A theory of creating a place or object that is free from the force of
gravity. It does not refer to the lack of weight under gravity experienced in
free fall or
orbit, or to balancing the force of gravity with some other force, such as electromagnetism or aerodynamic lift.
In
particle physics, every type of
particle has an associated antiparticle with the same
mass but with opposite
physical charges such as
electric charge. For example, the antiparticle of the
electron is the
antielectron (which is often referred to as the positron). While the electron has a negative electric charge, the positron has a positive electric charge, and is produced naturally in certain types of
radioactive decay. Some particles, such as the
photon, are their own antiparticle. Otherwise, for each pair of antiparticle partners, one is designated as "normal" matter (the kind comprising all matter with which humans usually interact), and the other (usually given the prefix "anti-") as
antimatter.
It is a subatomic particle of the same mass as a proton but having a negative electric charge and oppositely directed magnetic moment. It is the proton’s antiparticle. Antiprotons were first produced and identified in 1955 by Emilio Segrè, Owen Chamberlain[17]
A physical principle which states that the upward
buoyant force that is exerted on a body immersed in a
fluid, whether fully or partially submerged, is equal to the
weight of the fluid that the body
displaces and acts in the upward direction at the center of mass of the displaced fluid.[18]
The branch of
astronomy that deals with the physics of the
Universe, especially with the compositional nature of celestial bodies rather than their positions or motions in space.
A basic unit of
matter that consists of a dense central nucleus surrounded by a cloud of negatively charged
electrons. The atomic nucleus contains a mix of positively charged
protons and electrically neutral
neutrons.
A periodic vibration whose frequency is in the band audible to the average human, the human hearing range. It is the property of sound that most determines pitch, with a generally accepted standard hearing range for humans is 20 to 20,000 Hz. Also known as audible frequency (AF)
The ratio of the number of constituent
particles in a substance, usually
atoms or
molecules, to the
amount of substance, of which the
SI unit is the mole. It is defined as exactly 6.02214076×1023 mol−1.
A physical law which states that volumes of gases which are equal to each other at the same temperature and pressure will contain equal numbers of molecules.
A hypothetical
subatomic particle postulated to account for the rarity of processes that break charge-parity symmetry. It is very light, electrically neutral, and pseudoscalar.
A theorem concerning
diffraction which states that the diffraction pattern from an opaque body is identical to that from a hole of the same size and shape except for the overall forward beam intensity.
A structural element that is capable of withstanding load primarily by resisting bending. Beams are traditionally descriptions of building or civil engineering
structural elements, but smaller structures such as truck or automobile frames, machine frames, and other mechanical or structural systems contain beam structures that are designed and analyzed in a similar fashion.
The reaction induced in a
structural element when an external
force or
moment is applied to the element, causing the element to
bend.[20][21] The simplest structural element subjected to bending moments is the
beam.
for an arbitrary
complex numberα, the order of the Bessel function. Although α and −α produce the same differential equation, it is conventional to define different Bessel functions for these two values in such a way that the Bessel functions are mostly smooth functions of α. The most important cases are when α is an
integer or
half-integer. Bessel functions for integer α are also known as cylinder functions or the cylindrical harmonics because they appear in the solution to
Laplace's equation in
cylindrical coordinates. Spherical Bessel functions with half-integer α are obtained when the
Helmholtz equation is solved in
spherical coordinates.
The mechanical energy required to disassemble a whole into separate parts. A bound system typically has a lower
potential energy than the sum of its constituent parts.
A hypothetical idealized physical body that completely absorbs all incident
electromagnetic radiation, regardless of
frequency or
angle of incidence. Perfect black bodies are imagined as substitutes for actual physical bodies in many theoretical discussions of
thermodynamics, and the construction of nearly perfect black bodies in the real world remains a topic of interest for materials engineers. Contrast white body.
The type of
electromagnetic radiation within or surrounding a body in thermodynamic equilibrium with its environment, or emitted by a
black body (an opaque and non-reflective body) held at constant, uniform temperature. The radiation has a specific spectrum and intensity that depends only on the temperature of the body.
The phenomenon by which the
boiling point of a
liquid (a
solvent) increases when another compound is added, meaning that the resulting
solution has a higher boiling point than the pure solvent. This happens whenever a non-volatile solute, such as a salt, is added to a pure solvent, such as water. The boiling point can be measured accurately using an
ebullioscope.
The angle of incidence at which
light with a particular
polarization is completely transmitted through a transparent
dielectric surface, with no
reflection. When unpolarized light is incident at this angle, the light that is reflected is consequently perfectly polarized.
An Imperial unit of
energy defined as the amount of energy needed to heat one pound of water by one degree Fahrenheit; 1 btu is equal to about 1,055
joules. In scientific contexts the btu has largely been replaced by the SI unit of energy, the joule.
The tendency of a material to break without significant
plasticdeformation when subjected to
stress. Brittle materials absorb relatively little energy prior to fracture, even those of high strength. Breaking is often accompanied by a snapping sound.
The presumably random movement of particles suspended in a fluid (liquid or gas) resulting from their bombardment by fast-moving
atoms or molecules in the gas or liquid.
A measure of a substance's resistance to uniform
compression defined as the ratio of the infinitesimal pressure increase to the resulting relative decrease of the volume. Its base unit is the
pascal.
A branch of
mathematics that studies change and has two major sub-fields:
differential calculus (concerning rates of change and slopes of curves), and
integral calculus (concerning accumulation of quantities and the areas under and between curves). These two branches are related to each other by the fundamental theorem of calculus.
The ratio of the change in the
electric charge of a system to the corresponding change in its
electric potential. There are two closely related notions of capacitance: self capacitance and mutual capacitance. Any object that can be electrically charged exhibits self capacitance. A material with a large self capacitance holds more electric charge at a given
voltage than one with low capacitance. The notion of mutual capacitance is particularly important for understanding the operations of the
capacitor, one of the three elementary
linear electronic components (along with
resistors and
inductors).
A theoretical ideal
thermodynamic cycle proposed by French physicist
Nicolas Léonard Sadi Carnot in 1824 and expanded upon by others in the 1830s and 1840s. It provides an upper limit on the efficiency that any classical thermodynamic engine can achieve during the conversion of
heat into
work, or conversely, the efficiency of a
refrigeration system in creating a temperature difference by the application of work to the system. It is not an actual thermodynamic cycle but is a theoretical construct.
A
coordinate system that specifies each
point uniquely in a
plane by a set of
numerical coordinates, which are the
signed distances to the point from two fixed
perpendicular oriented lines, measured in the same
unit of length. Each reference line is called a coordinate axis or just axis (plural axes) of the system, and the point where they meet is called the origin, at ordered pair (0, 0). The coordinates can also be defined as the positions of the
perpendicular projections of the point onto the two axes, expressed as signed distances from the origin.
The electrode through which a conventional
electric current flows out of a polarized electrical device; the direction of current flow is, by convention, opposite to the direction of
electron flow, and so electrons flow into the cathode. In a
galvanic cell, the cathode is the positive terminal or pole which accepts electrons flowing from the external part of an
electrical circuit. However, in an
electrolytic cell, the cathode is the wire or plate having excess negative charge, so named because positively charged
cations tend to move towards it. Contrast anode.
The point in a body around which the resultant
torque due to
gravity forces vanish. Near the surface of the earth, where gravity acts downward as a parallel force field, the center of gravity and the
center of mass are the same.
The apparent outward force that draws a rotating body away from the centre of rotation. It is caused by the
inertia of the body as the body's path is continually redirected.
Any attempt in mainstream physics to
unify existing theories of
relativity,
gravitation, and
quantum mechanics, particularly by envisioning the three universal constants fundamental to each field – the
speed of light (), the
gravitational constant (), and the
Planck constant () – as the edges of a three-dimensional cube, at each corner of which is positioned a major sub-field within
theoretical physics according to which of the three constants are accounted for by that sub-field and which are ignored. One corner of this so-called "cube of theoretical physics", where all three constants are accounted for simultaneously, has not yet been satisfactorily described:
quantum gravity.
A branch of
chemistry and physics that studies chemical processes from the point of view of physics by investigating physicochemical phenomena using techniques from atomic and molecular physics and
condensed matter physics.
A type of light–matter interaction in which a
photon is scattered by a
charged particle, usually an
electron, which results in part of the energy of the photon being transferred to the recoiling electron; a resulting decrease in the energy of the photon is called the Compton effect. The opposite phenomenon occurs in inverse Compton scattering, when a charged particle transfers part of its energy to a photon.
The
motion of a moving particle or object that conforms to a known or fixed curve. Such motion is studied with two coordinate systems: planar motion and cylindrical motion.
Any influence upon or within an
oscillatory system that has the effect of reducing, restricting, or preventing its oscillations. Damping is a result of processes that dissipate the energy stored in the oscillation.
For a mathematical function of a
real variable, a measurement of the sensitivity to change of the function value (output) with respect to a change in its argument (input); e.g. the derivative of the position of a moving object with respect to time is the object's
velocity and measures how quickly the position of the object changes as time changes. Derivatives are a fundamental tool of
calculus.
An electrical
insulator that can be
polarized by an applied
electric field. When a dielectric material is placed in an electric field, electric charges do not flow through the material as they would in a
conductor but only shift slightly from their equilibrium positions, with positive charges displaced in the direction of the field's flow and negative charges displaced in the opposite direction; this creates an internal electric field that reduces the larger field within the dielectric material.
1. (fluid) Occurs when an object is immersed in a fluid, pushing it out of the way and taking its place. The volume of the immersed object will be exactly equal to the volume of the displaced fluid, so that the volume of the immersed object can be deduced if the volume of the displaced fluid is measured.
2. (vector) The shortest distance from the initial to the final position of a point. Thus, it is the length of an imaginary straight path, typically distinct from the path actually travelled by.
The change in
frequency of a
wave (or other periodic event) for an observer moving relative to its source. Compared to the emitted frequency, the received frequency is higher during the approach, identical at the instant of passing by, and lower during the recession.
Forces which act on a solid object in the direction of the relative fluid flow velocity. Unlike other resistive forces, such as dry
friction, which is nearly independent of velocity, drag forces depend on velocity.
A physical property of
matter that causes it to experience a
force when near other electrically charged matter. There are two types of electric charge: positive and negative.
The region of space surrounding electrically
charged particles and time-varying
magnetic fields. The electric field represents the force exerted on other electrically charged objects by the electrically charged particle the field is surrounding.
The electrical intensity or "pressure" developed by a source of electrical energy such as a
battery or
generator and measured in
volts. Any device that converts other forms of
energy into electrical energy provides electromotive force as its output.
A unit of
energy equal to approximately 1.6×10−19joule. By definition, it is the amount of energy gained by the charge of a single
electron moved across an electric potential difference of one
volt.
A field that deals with
electrical circuits that involve active electrical components such as vacuum tubes, transistors, diodes, and integrated circuits as well as associated passive interconnection technologies.
An adjective used to refer to a process or reaction in which a system absorbs
energy from its surroundings, usually in the form of
heat but also in the form of
light,
electricity, or
sound. Contrast exothermic.
The
velocity at which the
kinetic energy plus the gravitational
potential energy of an object is zero. It is the speed needed to "escape" from a gravitational field without further propulsion.
An adjective used to refer to a process or reaction that releases
energy from a system, usually in the form of
heat but also in the form of
light,
electricity, or
sound. Contrast endothermic.
Either a nuclear reaction or a radioactive decay process in which the nucleus of an atom splits into smaller parts (lighter nuclei), often producing free neutrons and photons (in the form of gamma rays) and releasing relatively large amounts of energy.
A push or pull. Any interaction that, when unopposed, will change the
motion of a physical body. A force has both magnitude and direction, making it a
vector quantity. The
SI unit used to measure force is the
newton.
A model used to explain the influence that a massive body extends into the space around itself, producing a
force (
gravity) on another massive body. Thus, a gravitational field is used to explain and represent gravitational phenomena. It is measured in
newtons per kilogram (N/kg).
The gravitational potential at a location is equal to the
work (
energy transferred) per unit
mass that is done by the force of
gravity to move an object to a fixed reference location.
A ripple in the curvature of
spacetime that propagates as a
wave and is generated in certain gravitational interactions, travelling outward from their source.
The time required for a quantity to fall to half its value as measured at the beginning of the time period. In physics, half-life typically refers to a property of
radioactive decay, but may refer to any quantity which follows an exponential decay.
The modern form of the metric system, comprising a system of units of measurement devised around seven base units and the convenience of the number ten.
A variant of a particular chemical element. While all isotopes of a given element share the same number of
protons, each isotope differs from the others in its number of
neutrons.
The branch of
classical mechanics that describes the
motion of points, bodies (objects), and systems of bodies (groups of objects) without consideration of the causes of motion. The study of kinematics is often referred to as the "geometry of motion".
The
energy that a physical body possesses due to its
motion, defined as the
work needed to
accelerate a body of a given
mass from rest to its stated
velocity. The body continues to maintain this kinetic energy unless its velocity changes. Contrast potential energy.
A
vector used chiefly to describe the shape and orientation of the orbit of one astronomical body around another, such as a planet revolving around a star. For two bodies interacting by Newtonian gravity, the LRL vector is a constant of motion, meaning that it is the same no matter where it is calculated on the orbit; equivalently, the LRL vector is said to be conserved.
A device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation. The word "laser" is an acronym for "light amplification by stimulated emission of radiation"
An elementary particle which does not undergo
strong interactions but is subject to the
Pauli exclusion principle. Two main classes of leptons exist: charged leptons (also known as the
electron-like leptons) and neutral leptons (better known as
neutrinos).
The mathematical study of how solid objects deform and become internally stressed due to prescribed loading conditions. Linear elasticity is a simplification of the more general
nonlinear theory of elasticity and is a branch of
continuum mechanics.
A
state of matter which has properties between those of a conventional liquid and those of a solid crystal. For instance, an LC may flow like a liquid, but its
molecules may be oriented in a crystal-like way.
The proposition that the existence of absolute rotation (the distinction of local inertial frames vs. rotating reference frames) is determined by the large-scale distribution of matter.
Any powered tool consisting of one or more parts that is constructed to achieve a particular goal. Machines are usually powered by mechanical, chemical, thermal or electrical means, and are frequently motorised.
A mathematical description of the
magnetic influence of
electric currents and magnetic materials. The magnetic field at any given point is specified by both a direction and a magnitude (or strength); as such it is a
vector field.
The rate of mass flow per unit area. The common symbols are j, J, φ, or Φ, sometimes with subscript m to indicate mass is the flowing quantity. Its SI units are kg s−1 m−2.
An interdisciplinary field incorporating elements of physics, chemistry, and engineering that is concerned with the design and discovery of new materials, particularly
solids.
The application of
mathematics to problems in physics and the development of mathematical methods suitable for such applications and for the formulation of physical theories.
A rectangular array of numbers, symbols, or expressions arranged in rows and columns. The individual items in a matrix are called its elements or entries.
A set of partial differential equations that, together with the Lorentz force law, form the foundation of classical electrodynamics, classical optics, and electric circuits. Maxwell's equations describe how
electric and
magnetic fields are generated and altered by each other and by
charges and
currents.
A term which relates to the way in which quantitative data tend to cluster around some value. A measure of central tendency is any of a number of ways of specifying this "central value".
The branch of science concerned with the behaviour of physical bodies when subjected to
forces or displacements and the subsequent effects of the bodies on their environment.
The mathematical description of an object's or substance's tendency to be
deformed elastically (i.e. non-permanently) when a force is applied to it. The elastic modulus of an object is defined as the slope of its
stress–strain curve in the elastic deformation region. As such, a
stiffer material will have a higher elastic modulus.
An electrically neutral group of two or more
atoms held together by covalent chemical bonds. Molecules are distinguished from
ions by having a net
electric charge equal to zero.
A branch of physics that studies the physical properties of
molecules and the chemical bonds between
atoms as well as their molecular dynamics. It is closely related to atomic physics and overlaps greatly with theoretical chemistry,
physical chemistry and
chemical physics.
Any change in the position of an object over
time. Motion can be mathematically described in terms of
displacement,
distance,
velocity,
speed,
acceleration, and
momentum, and is observed by attaching a
frame of reference to an observer and measuring the change in an object's position relative to that frame. An object's motion cannot change unless it is acted upon by a
force.
An elementary particle, technically classified as a
lepton, that is similar to the
electron, with unitary negative electric charge (−1) and a spin of 1⁄2. Muons are not believed to have any sub-structure.
The manipulation of matter on an
atomic and
molecular scale; a more generalized description by the
National Nanotechnology Initiative is "the manipulation of matter with at least one dimension sized from 1 to 100 nanometres".
A type of electrically neutral
subatomic particle denoted by the Greek letter ν (nu). All evidence suggests that neutrinos have
mass but that their mass is tiny even by the standards of subatomic particles. Their mass has never been measured accurately.
A set of three physical laws which describe the relationship between the
forces acting on a body and its motion due to those forces. Together they form the basis for
classical or Newtonian mechanics.
An
atomic species characterized by the specific composition of its
nucleus, i.e. by its number of
protons, its number of
neutrons, and its nuclear
energy state.
An
optomechanical device used for the capture, analysis, and manipulation of
dielectric objects or particles, which operates via the application of
force by the
electric field of light.
The branch of physics which involves the behaviour and properties of
light, including its interactions with matter and the construction of instruments that use or detect it. Optics usually describes the behaviour of visible, ultraviolet, and infrared light; however, other forms of
electromagnetic radiation such as
X-rays, microwaves, and radio waves exhibit similar properties.
A principle in
fluid mechanics which states that
pressure exerted anywhere in a confined incompressible fluid is transmitted equally in all directions throughout the fluid such that the initial pressure variations remain the same.
A tabular display of the
chemical elements organised on the basis of their
atomic numbers, electron configurations, and recurring chemical properties. Elements are presented in order of increasing atomic number (number of protons).
The natural science that involves the study of
matter and its motion through
space and
time, along with related concepts such as
energy and
force. More broadly, it is the general analysis of
nature, conducted in order to understand how the
universe behaves.
A measure of the expectation that an event will occur or that a statement is true. Probabilities are given a value between 0 (will not occur) and 1 (will occur). The higher the probability of an event, the more certain one can be that the event will occur.
A
wheel on an axle that is designed to support movement of a cable or belt along its circumference; one of six classical
simple machines. Pulleys are used in a variety of ways to lift loads, apply
forces, and transmit
power.
A branch of physics dealing with physical phenomena at microscopic scales, where the action is on the order of the
Planck constant. Quantum mechanics departs from
classical mechanics primarily at the
quantum realm of
atomic and
subatomic length scales, and provides a mathematical description of much of the dual particle-like and wave-like behavior and interactions of energy and matter that occur at this scale.
An elementary
particle and a fundamental constituent of
matter. Quarks combine to form composite particles called
hadrons, the most stable of which are
protons and
neutrons, the components of
atomic nuclei.
Also called a radioactive nuclide, radioisotope, or radioactive isotope.
Any
nuclide possessing excess nuclear
energy to the point that it is unstable. Such excess energy is emitted through any of several processes of
radioactive decay, resulting in a
stable nuclide or sometimes another unstable radionuclide which can then undergo further decay. Certain radionuclides occur naturally; many others can be produced artificially in
nuclear reactors,
cyclotrons,
particle accelerators, or radionuclide generators.
A phenomenon which occurs when
light seen coming from an object that is moving away from the observer is proportionally increased in
wavelength or "shifted" to the
red end of the
visible light spectrum.
The change in direction of a
wave as it passes from one
transmission medium to another or as a result of a gradual change in the medium. Though most commonly used in the context of refraction of
light, other waves such as
sound waves and
fluid waves also experience refraction.
An idealization of a solid body in which
deformation is neglected. In other words, the
distance between any two given points of a rigid body remains constant in time regardless of the external forces exerted on it. Even though such an object cannot physically exist due to
relativity, objects can normally be assumed to be perfectly rigid if they are not moving near the
speed of light.
Any simple physical quantity that can be described by a single number (as opposed to
vectors,
tensors, etc., which are described by several numbers such as magnitude and direction) and is unchanged by coordinate system rotations or translations (in Newtonian mechanics) or by Lorentz transformations or central-time translations (in relativity).
The general physical process by which some forms of
radiation, such as
light,
sound, or moving particles, are forced to deviate from a straight
trajectory by one or more localised non-uniformities in the medium through which they pass.
A mechanical device that changes the direction or magnitude of a
force. In general, a set of six classical simple machines identified by Renaissance scientists drawing from Greek texts on technology are collectively defined as the simplest mechanisms that can provide mechanical advantage (also called leverage).
A tube in an inverted U shape that causes a liquid to flow uphill without pumps, powered by the fall of the liquid as it flows down the tube under the pull of
gravity. The term may also more generally refer to a wide variety of devices involving the flow of liquids through tubes.
The tendency of a solid, liquid, or gaseous chemical substance (called a solute) to dissolve in another solid, liquid, or gaseous substance (called a solvent) to form a homogeneous solution of the solute in the solvent. The solubility of a solute fundamentally depends on the specific solvent as well as on
temperature and
pressure.
A mechanical
wave that is an oscillation of
pressure transmitted through a solid, liquid, or gas and composed of frequencies within the range of human hearing.
A fundamental universal
physical constant defined as exactly 299,792,458 metres per second, a figure that is exact because the length of the metre is defined from this constant and the international standard for time. When not otherwise qualified, the term "speed of light" usually refers to the speed of
light in
vacuum, as opposed to the speed of light through some physical medium.
Any
nuclide that is not radioactive and does not spontaneously undergo
radioactive decay, as opposed to a
radionuclide. When such nuclides are referred to in relation to specific elements, they are usually termed
stable isotopes.
The branch of mechanics concerned with the analysis of loads (
force and
torque, or "moment") on physical systems in static equilibrium, that is, in a state where the relative positions of subsystems do not vary over time, or where components and structures are at a constant
velocity.
The transformation of a body from a reference configuration to a current configuration. A configuration is a set containing the positions of all particles of the body.
The physical process by which matter is transformed directly from the solid phase to the gas phase without passing through an intermediate liquid phase. Sublimation is an
endothermic phase transition that occurs at temperatures and pressures below a substance's
triple point in its phase diagram.
A phenomenon of exactly zero
electrical resistance and expulsion of
magnetic fields occurring in certain materials when cooled below a characteristic critical temperature.
A branch of physics that employs mathematical models and abstractions of physical objects and systems in order to rationalize, explain, and predict natural phenomena, as opposed to
experimental physics, which relies on data generated by experimental observations.
A state in which there is no net flow of
thermal energy between two physical systems when the systems are connected by a path permeable to heat. A system may also be said to be in thermal equilibrium with itself if the
temperature within the system is spatially and temporally uniform. Systems in
thermodynamic equilibrium are always in thermal equilibrium, but the converse is not always true.
The tendency of a
force to rotate an object about an axis, fulcrum, or pivot. Just as a force is a push or a pull, a torque can be thought of as a twist to an object.
The ability of a material to absorb
energy and plastically
deform without fracturing. Material toughness is defined as the amount of energy per unit volume that a material can absorb before rupturing. It is also defined as the resistance to fracture of a material when
stressed.
Any of a variety of mathematical inequalities asserting a fundamental limit to the precision with which certain pairs of physical properties of a
particle, such as position x and momentum p, cannot be known simultaneously.
A mathematical structure formed by a collection of elements called
vectors, which may be added together and multiplied ("scaled") by numbers called
scalars.
A
vector quantity defined as the
rate of change of the position of an object with respect to a given
frame of reference. Velocity specifies both an object's
speed and direction of
motion (e.g. 60 kilometres per hour to the north).
An instrument used for measuring the difference in
electric potential between two points in an
electric circuit. Analog voltmeters move a pointer across a scale in proportion to the
voltage of the circuit.
A derived unit of
power in the International System of Units (SI) defined as one joule per second. The watt measures the rate of energy conversion or transfer.
A wheel attached to an axle in such a way that the two parts rotate together and transfer forces between them; one of six classical
simple machines.
white body
A hypothetical idealized physical body that reflects all incident
electromagnetic radiation completely and uniformly in all directions; the opposite of a
black body.
A high-energy
photon (between 100
eV and 100 keV) with a wavelength shorter than that of ultraviolet radiation and longer than that of gamma radiation.
The effect of splitting a spectral line into several components in the presence of a static magnetic field by the lifting of degeneracy in electronic states.
^
abCummings, Karen; Halliday, David (2007).
Understanding physics. New Delhi: John Wiley & Sons Inc., authorized reprint to Wiley - India. pp. 449, 484, 485, 487.
ISBN978-81-265-0882-2.(UP1)