Physics. Dictionary

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Physics terms

A

Absolutely rigid body: a set of points whose distances between their current positions do not change, no matter what influences this body is subjected to in the process of interaction with other solid objects

Absolutely elastic body: a body which, after the cessation of the action of the cause that caused its deformation, completely restores its original dimensions and shape, that is, it has no residual deformation.

Absolute space: in classical mechanics — a three-dimensional Euclidean space in which the principle of relativity and Galilean transformations hold.

Aggregate state of matter: the physical state of matter, depending on the corresponding combination of temperature and pressure. A change in the aggregate state may be accompanied by an abrupt change in free energy, entropy, density and other physical quantities.

Traditionally, three aggregate states are distinguished: solid, liquid and gaseous. It is customary to include plasma among the aggregate states as well; gases pass into it when the temperature rises at a fixed pressure. A distinctive feature is the absence of a sharp boundary of transition to the plasma state. There are also other aggregate states.

Definitions of aggregate states are not always strict. Thus, there exist amorphous bodies that retain the structure of a liquid and possess a slight fluidity and the ability to retain their shape; liquid crystals are fluid, but at the same time possess some properties of solids, in particular, they can polarize the electromagnetic radiation passing through them.

State of matter

Alpha particle: a particle consisting of two protons and two neutrons, emitted by atomic nuclei during radioactive decay.

Amplitude: the height of the wave crests.

The maximum value of the displacement or change of a variable from the mean value during oscillatory or wave motion. A non-negative scalar quantity whose dimension coincides with the dimension of the physical quantity being determined.

Atmospheric pressure: the pressure created by atmospheric air; at sea level the normal atmospheric pressure is 760 millimeters of mercury.

Atom: a particle of matter of microscopic size and mass, the smallest part of a chemical element, which is the carrier of its properties. It consists of nucleus and electron cloud

Aerodynamics: the science of the forces acting on bodies moving in the air.

Aerodynamic profile: any body resembling an aircraft wing and intended to produce lift when moving in the air.

B

Baryons (from Greek βαρύς — heavy) — a family of elementary particles: strongly interacting fermions consisting of three quarks.

The main baryons include (in order of increasing mass): proton, neutron, lambda baryon, sigma hyperon, xi hyperon, omega hyperon. The mass of the omega hyperon (3278 electron masses) is almost 1.8 times greater than the mass of the proton.

Baryons, together with mesons (the latter consist of an even number of quarks), make up the group of elementary particles participating in the strong interaction and called hadrons.

You can study a detailed classification of elementary particles here

Battery: an element consisting of a mixture of chemical compounds and creating an electromotive force when connected to an electrical circuit.

Beta particle: an elementary particle (either an electron or a positron), emitted in a number of cases by atomic nuclei during radioactive decay.

Brownian motion: — the random motion of microscopic visible suspended particles of a solid substance in a liquid or gas, caused by the thermal motion of the particles of the liquid or gas.

V

Vacuum: space free of matter. In engineering and applied physics, vacuum is understood as a medium consisting of gas at a pressure significantly below atmospheric.

Vector: a quantity characterized by a numerical value and a direction.

Weight: the force with which a body acts on a support (or suspension, or another type of attachment) that prevents it from falling, arising in the field of gravity . The unit of weight in the International System of Units (SI) is the newton; sometimes the CGS unit, the dyne, is used.

Concave surface: the surface of a body curved inward, such as, for example, the inner surface of a hollow sphere.

Wave: a change in a certain set of physical quantities (characteristics of a certain physical field or material medium) that is capable of moving, moving away from the place of its origin, or oscillating within limited regions of space.

Voltmeter: a device for measuring electrical voltage or EMF.

Voltmeter

Time: a form of the course of physical and mental processes, a condition for the possibility of change. One of the basic concepts of philosophy and physics, a measure of the duration of the existence of all objects, a characteristic of the successive change of their states in processes and of the processes themselves, of change and development, and also one of the coordinates of a single space-time, ideas about which are being developed in the theory of relativity.

Mechanical advantage: the degree of transformation by a simple machine of the effort required to do work.

Convex surface: the surface of a body curved outward, such as, for example, the outer surface of a sphere.

Buoyant force: a force directed vertically upward and equal to the weight of the gaseous or liquid substance displaced by the body.

Viscosity: the property of liquids to offer resistance to flow due to the presence of friction forces between its particles.

G

Geiger counter: a device that measures radioactivity by recording the number of charged particles entering it that were released as a result of the decay of atomic nuclei.

Generator: any machine that converts mechanical motion into electric current.

Geothermal energy: the energy of steam formed naturally in deep underground wells. This steam is usually used to rotate the rotor of a turbine and then generate electricity.

Gravitational field: the space in which the action of the gravitational attraction of bodies is felt.

D

Saturated vapor pressure: the pressure created near the surface of a liquid by its evaporated molecules.

Real image: an image formed by a lens or mirror at the place where light rays intersect.

Diode: a device that passes current in only one direction.

Diffraction: the property of light waves to bend around the edges of an oncoming obstacle.

Wavelength: the distance between two adjacent crests of a wave.

Doppler effect: a phenomenon in which the frequency and, accordingly, the pitch of a sound wave become higher for the listener if the sound source approaches, and lower if the sound source moves away.

Yo

Capacitance: a characteristic of a conductor characterizing its ability to accumulate electric charge.

Capacitance is defined as the ratio of the magnitude of the charge of the conductor to the potential of the conductor. Capacitance is denoted as C.

Read more in the article «Capacitance of a capacitor»

Zh

Liquid: a substance in a liquid aggregate state, occupying an intermediate position between the solid and gaseous states.

At the same time aggregate state of a liquid, like the aggregate state of a solid body, is condensed, that is, one in which the particles (atoms, molecules, ions) are bound to one another.

Sound wave: a mechanical wave formed by the alternating compression and expansion of the substance in which sound propagates.

I

Insulator: a substance that conducts heat or electric current poorly.

Inertia: the tendency of a moving body to maintain motion, and of a body at rest to maintain a state of rest.

Interference: the mutual amplification or weakening of light waves when they are superimposed on each other.

Evaporation: a process in which a liquid slowly turns into vapor.

K

Kinetic energy: a measure of the energy of a moving body; the faster the body moves, the higher its kinetic energy.

Convection: a process in which heat circulates within a volume of liquid or gas.

Condensation: a process in which a substance passes from a gaseous to a liquid or solid state.

N-type silicon: silicon having an excess of negative charges.

P-type silicon: silicon having an excess of positive charges.

Torque: any force tending to set a body into rotation.

L

Laser: a device that creates a powerful beam of light radiation having only one wavelength.

Drag: the friction force that reduces the speed of bodies moving in the air.

Luminescent glow: light obtained by exciting the atoms of gaseous mercury with an electric current; these atoms then emit electromagnetic radiation which, falling on phosphorus, makes it glow.

M

Magnetism: the force of attraction or repulsion that arises between two bodies whose molecules are oriented in such a way as to create a resulting magnetic field.

Magnetic field: the space in which the action of the attractive and repulsive forces of a magnet is felt.

Mass: a measure of the amount of matter in a body, determined by its ability to resist acceleration.

N

Neutrino: an electrically neutral elementary particle whose mass is negligibly small or equal to zero.

Neutrons: elementary particles that, together with protons and electrons, make up the atoms of substances; neutrons are located in the atomic nucleus and have no electric charge.

Filament: a thin wire in incandescent lamps that emits light when heated by electric current.

Newton: The unit of force in the International System of Units SI. Named after the English scientist Isaac Newton. Russian designation N. International designation N.

One newton is defined as the force that changes the speed of a body of mass 1 kg by 1 m/s in 1 second in the direction of the force. Thus, 1 N = 1 kg·m/s².

O

Overtone: a sound created by a standing wave whose length is an integer number of times less than the wavelength of the fundamental tone.

Objective lens: a lens in some types of telescopes that forms an image of an object perceived by the observer's eye.

Volume: a quantitative measure of the space occupied by a substance.

The ocean as an energy source: a method of obtaining electricity by evaporating a low-boiling liquid with the heat of the surface layers of water; the resulting steam is used to rotate a turbine connected to an electric generator.

Oxidizer: a component of rocket fuel containing the oxygen necessary for its combustion.

Eyepiece: a lens of an optical system facing the observer's eye.

Reference wave: a beam of light used in obtaining holograms; it falls on the same area of the photographic film as the object wave, but passes by the object being photographed.

Organic fuel: any substance such as oil, coal or natural gas formed as a result of the decomposition of organic compounds millions of years ago.

Ground state: the lowest energy level of an electron.

Fundamental tone: the sound corresponding to the greatest wavelength of a standing wave; in musical instruments, the fundamental tone is the lowest-frequency of the sounds they produce.

Oscilloscope: a device that converts sound waves into electrical signals and displays them on a screen.

Sympathetic vibrations: a phenomenon in which sound waves created by a vibrating body, for example a tuning fork, cause an identical body nearby to vibrate as well.

Reflection: the property of light or sound to be reflected from oncoming surfaces.

P

Voltage drop: a decrease in voltage in a circuit associated with the passage of electric current through a resistance.

Vaporization: the process of transition of substances from the solid or liquid state to the gaseous state.

Gear ratio: this is the ratio of the number of teeth or diameters of the gears that are in direct engagement or covered by a common chain.

Alternating current: an electric current that periodically changes its direction.

Density: the ratio of the mass of a body to its volume.

Positron: an elementary particle having the same mass as an electron but possessing a positive charge.

Semiconductor: a material that, like silicon, conducts electric current under some conditions and does not under others.

Magnet poles: the ends of a magnet, called the south and north poles, which are the regions of entry and exit of the magnetic field lines, respectively.

Transverse wave: a wave in which the motion of the medium is perpendicular to the direction of motion of the wave front.

Direct current: an electric current flowing in only one direction.

Right-hand rule: a mnemonic rule for determining the direction of a vector product. Read more in the article «Right-hand rule»

Elastic limit: the maximum force after the removal of which a compressed or stretched spring fully restores its original shape. Any applied force exceeding the elastic limit will cause residual deformation of the spring.

Object wave: a beam of laser radiation reflected from the object being photographed onto the photographic film; used in obtaining holograms.

Refraction: the property of light or sound to change its direction when passing from one medium to another.

Prism: a device that decomposes white light into its constituent colors: red, orange, yellow, green, cyan, blue and violet.

Galileo's principle of relativity: a fundamental physical principle for the laws of classical mechanics, one of the principles of symmetry, according to which all physical processes in inertial reference frames proceed in the same way, regardless of whether the system is at rest or is in a state of uniform and rectilinear motion.

Einstein's principle of relativity: a fundamental physical principle, one of the principles of symmetry, according to which all physical processes in inertial reference frames proceed in the same way, regardless of whether the system is at rest or is in a state of uniform and rectilinear motion.

Conductor: a material that conducts electric current.

Protons: elementary particles that, together with neutrons and electrons, make up the atoms of substances. Protons are located in the atomic nucleus and have a positive charge.

Antinode: the point at which a standing wave has maximum amplitude.

R

Radioactivity: the energy released during the decay of atomic nuclei.

Rocket fuel: a substance that creates thrust as a result of combustion.

S

Superconductivity: the ability of some substances, when cooled to very low temperatures, to conduct electric current without resistance.

Light: electromagnetic radiation in the wavelength range from 0.000038 to 0.000076 cm; such wavelengths are perceived by the human eye as colors.

Incandescent lamp light: light emitted by the filament when it is heated by electric current.

Lorentz force: the force with which an electromagnetic field, according to classical (non-quantum) electrodynamics, acts on a point charged particle. Sometimes the Lorentz force is called the force acting on a charge q moving with velocity v only from the side of the magnetic field, and quite often the total force — from the side of the electromagnetic field in general, in other words, from the side of the electric E and magnetic B fields.

Read more about determining the direction of the Lorentz force in the article «Right-hand rule»

Gravity: — the force acting on any physical body near the surface of an astronomical object (planet, star) and consisting of the force of gravitational attraction of this object and the centrifugal force of inertia caused by its daily rotation.

Shock wave: the loud noise produced by the rapid expansion of air when a body moves at supersonic speed.

Solenoid: a wire coil wound on a ferromagnetic core for use as an electromagnet.

Solar energy conversion: the process of obtaining electricity from the energy of the sun. Solar radiation can be used to turn water into steam that rotates a turbine, or to power solar batteries.

Static electricity: an electric charge accumulated by a body, either negative (with an excess of electrons) or positive (with a lack of them).

Scintillation counter: a device that produces an electrical signal when a charged particle enters it.

T

Timbre: the characteristic sound of a musical instrument; determined by the range of tones of the instrument and the materials from which it is made.

Temperature: an indirect measure of the average speed of vibration of the molecules of a substance.

Thermal energy: a quantitative measure of the internal energy of a substance; it is the sum of the kinetic energy of the molecules of the substance, determined by its temperature.

Thermal conductivity: the ability of bodies to conduct heat to one degree or another.

Heat of phase transition: the energy required to accomplish a phase transition in a substance.

Thermal power engineering: a method of producing electricity in which the heat released during the combustion of organic fuel turns water into steam; this steam then rotates the blade wheel of a turbine.

Boiling point: the temperature at which a substance passes from the liquid state to the vapor state.

Transition point: the temperature at which a conductor of electricity completely loses resistance and becomes a superconductor.

Transistor: a semiconductor that can be used as a switch in electronic circuits.

Friction: the force opposing the relative displacement of bodies in contact.

Gravitational force: the force responsible for the mutual attraction of separated masses. The gravitational force between two bodies is proportional to the mass of these bodies and inversely proportional to the square of the distance between them.

U

Angular momentum: a measure of the rotational energy of a body; the magnitude of the angular momentum depends on the mass of the body and the angular velocity of its rotation.

Node: the point at which a standing wave has zero amplitude.

F

Ferromagnetic material: a material that can be magnetized, for example iron.

Physics: a field of natural science: the science of the most general laws of nature, of matter, its structure, motion and the rules of transformation.

The concepts of physics and its laws underlie all natural science. It is an exact science.

Focal point: the point at which all light rays reflected from a mirror or passing through a lens converge.

Focal length: the distance from the focal point to the center of the lens or mirror.

Phosphorus: a chemical element that emits visible light when excited by radiation.

Wave front: the moving crest of a wave.

Ts

Circuit: a closed loop through which electric current flows. Resistances in a circuit can be connected in parallel (in this case each resistance is installed in a separate branch of the circuit) and in series, i.e. one after another.

Ch

Frequency: the number of crests of a moving wave passing through a given point in one second.

E

Electrical voltage: the force that causes the acceleration of electrons in a closed conducting circuit and thereby creates an electric current.

Voltage

Read more in the article «Potential difference»

Electrical resistance: — a physical quantity characterizing the property of a conductor to impede the passage of electric current and equal to the ratio of the voltage at the ends of the conductor to the current strength flowing through it.

Electrical resistance

Electricity: a field created by a charged particle; a stationary particle creates static electricity, a moving one creates an electric current.

Electromotive force (voltage): the force that causes the acceleration of electrons in a closed conducting circuit and thereby creates an electric current.

Electromagnet: a magnet made in the form of a coil with current surrounding a core of ferromagnetic material; the electric current induces a magnetic field in the core.

Electromagnetic induction: the phenomenon of the emergence of an electric current in a conductor crossing the lines of force of a magnetic field.

Electromagnetic radiation: the transfer of energy by means of electromagnetic waves (photons) moving at the speed of light; as they propagate, electromagnetic waves generate both an electric and a magnetic field. The energy of an electromagnetic wave is inversely proportional to the wavelength of the radiation. Gamma radiation has the highest energy and the shortest wavelength; then, in order of decreasing energy and increasing wavelength, come: X-ray radiation, ultraviolet radiation, visible light, infrared radiation and radio waves.

Electron cloud: a visual model reflecting the distribution of the probability density function of finding an electron in an atom or molecule depending on the energy of the electron.

Electron cloud

Electrons: elementary particles that, together with protons and neutrons, make up the atoms of substances. Electrons have a negative electric charge and orbit around the atomic nucleus.

Electrons

Energy level: one of the orbits on which the electrons of an atom can be located.

Yu

Young's modulus: — a physical quantity characterizing the ability of a material to resist tension and compression under elastic deformation.

Synonyms: modulus of longitudinal elasticity, modulus of normal elasticity.

Young's modulus

Ya

Nuclear energy: the energy released during the radioactive decay of atomic nuclei. It is usually used to turn water into steam, which then rotates a turbine connected to an electric generator.

Nucleus: the central part of atom , around which electrons move in orbit; it consists of protons and neutrons.

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Article author: Andrei Olegovich