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GLOSSARY OF PHYSICS TERMS

Absolute humidity (or Saturation value) The maximum amount of water vapor, which could be present in 1 m³ of the air at any given temperature, is called absolute humidity.

Absolute magnitude A classification scheme, which compensates for the distance, differences to stars. It calculates the brightness that stars would appear to have if they were all at a defined, standard distance of 10 parsec

Absolute scale Temperature scale set so that zero is at the theoretical lowest temperature possible. This would occur when all random motion of molecules has ceased

Absolute zero The theoretical lowest temperature possible, which occurs when all random motion of molecules has ceased

Acceleration due to gravity The acceleration produced in a body due to the earth's attraction is called acceleration due to gravity. It is denoted by the letter g. Its SI unit is m/s². On the surface of the earth, its average value is 9.8m/s². The value of g on the surface of the earth increases in going towards the poles from the equator. The acceleration due to gravity of the earth decreases with altitude and with depth inside the earth. The value of g at the center of the earth is zero.

Acceleration The rate of change of velocity of a moving object is called its acceleration. The SI units of acceleration are m / s². By definition, this change in velocity can result from a change in speed, a change in direction, or a combination of changes in speed and direction

Adiabatic cooling The decrease in temperature of an expanding gas that involves no additional heat flowing out of the gas. It is the cooling from the energy lost by expansion

Adiabatic heating The increase in temperature of compressed gas that involves no additional heat flowing into the gas. It is heating from the energy gained by compression

Air mass A large, more or less uniform body of air with nearly the same temperature and moisture conditions throughout

Allotropic forms Elements that can have several different structures with different physical properties-for example, graphite and diamond are two allotropic forms of carbon

Alpha particle The nucleus of a helium atom (two protons and two neutrons) emitted as radiation from a decaying heavy nucleus; also known as an alpha ray

Alternating current An electric current that first moves one direction, then the opposite direction with a regular frequency

Amp Unit of electric current. It is equivalent to coulomb/sec.

Ampere Full name of the unit Amp

Amplitude (of waves) The maximum displacement of particles of the medium from their mean positions during the propagation of a wave is called the amplitude of the wave.

Amplitude (of an oscillation) The maximum displacement of a body from its mean position during an oscillatory motion is called the amplitude of oscillation.

Angle of reflection Angle of a reflected ray or particle from a surface; measured from a line perpendicular to the surface (the normal)

Angular Acceleration The rate of change of angular velocity of a body moving along a circular path is called its angular acceleration. Angular acceleration is denoted by a.

Angular Displacement The angle described at the center of the circle by a moving body along a circular path is called angular displacement. It is measured in radians.

Angular Momentum Quantum Number From quantum mechanics model of the atom, one of four descriptions of the energy state of an electron wave. The quantum number describes the energy sublevels of electrons within the main energy levels of an atom

Angular Velocity The rate of change of angular displacement is called angular velocity.

Astronomical unit The radius of the earth's orbit is defined as one astronomical unit (A.U.)

Atom The smallest unit of an element that can exist alone or in combination with other elements

Atomic mass unit Relative mass unit (u) of an isotope based on the standard of the carbon-12 isotope, which is defined as a mass of exactly 12.00 u; one atomic mass unit (I u) is 1/12 the mass of a carbon-12 atom

Atomic number The number of protons in the nucleus of an atom

Atomic Weight Weighted average of the masses of stable isotopes of an element as they occur in nature, based on the abundance of each isotope of the element and the atomic mass of the isotope compared to carbon-12

Avogadro's Number The number of carbon-12 atoms in exactly 12.00 g of C that is 6.02 x 10^23 atoms or other chemical units. It is the number of chemical units in one mole of a substance

Axis The imaginary line about which a planet or other object rotates

Background Radiation Ionizing radiation (alpha, beta, gamma, etc.) from natural sources

Balanced Forces When a number of forces act on a body, and the resultant force is zero, then the forces are said to be resultant forces.

Balmer series A set of four line spectra, narrow lines of color emitted by hydrogen atom electrons as they drop from excited states to the ground state

Barometer An instrument that measures atmospheric pressure, used in weather forecasting and in determining elevation above sea level

Beat Rhythmic increases and decreases of volume from constructive and destructive interference between two sound waves of slightly different frequencies

Beta particle High-energy electron emitted as ionizing radiation from a decaying nucleus; also known as a beta ray

Big bang theory Current model of galactic evolution in which the universe was created from an intense and brilliant explosion from a primeval fireball

Binding energy The energy required to break a nucleus into its constituent protons and neutrons; also the energy equivalent released when a nucleus is formed

Black hole The theoretical remaining core of a supernova that is so dense that even light cannot escape

Blackbody radiation Electromagnetic radiation emitted by an ideal material (the blackbody) that perfectly absorbs and perfectly emits radiation

Bohr model Model of the structure of the atom that attempted to correct the deficiencies of the solar system model and account for the Balmer series

Boiling point The temperature at which a phase change of liquid to gas takes place through boiling. It is the same temperature as the condensation point

Boundary The division between two regions of differing physical properties

British thermal unit The amount of energy or heat needed to increase the temperature of one pound of water one degree Fahrenheit (abbreviated Btu)

Cathode rays Negatively charged particles (electrons) that are emitted from a negative terminal in an evacuated glass tube

Celsius scale of temperature In the celsius scale of temperature, the ice-point is taken as taken as the lower fixed point (0 deg C ) and the steam-point is taken as the upper fixed point (100 deg C). The interval between the ice point and steam point is divided into 100 equal divisions. Thus, the unit division on this scale is 1degC. This scale was earlier called the centigrade scale. 1 deg C = 9/5 deg F.

Centigrade Alternate name for the Celsius scale

Centrifugal force An apparent outward force on an object following a circular path that. This force is a consequence of the third law of motion

Centripetal force The force required to pull an object out of its natural straight-line path and into a circular path; centripetal means

Chain reaction A self-sustaining reaction where some of the products are able to produce more reactions of the same kind; in a nuclear chain reaction neutrons are the products that produce more nuclear reactions in a self-sustaining series

Circular Motion The motion of a body along a circular path is called circular motion.

Coefficient of cubical expansion The increase in volume of a substance per unit original volume per degree rise in temperature is called its coefficient of cubical expansion. The SI unit of coefficient of cubical expansion is K-1.

Coefficient of linear expansion The increase in length per unit original length per degree rise in temperature is called the coefficient of linear expansion. The SI unit of the coefficient of linear expansion is K-1.

Compression A part of a longitudinal wave in which the density of the particles of the medium is higher than the normal density is called a compression.

Compressive stress A force that tends to compress the surface as the earth's plates move into each other

Condensation (sound) A compression of gas molecules; a pulse of increased density and pressure that moves through the air at the speed of sound

Condensation (water vapor) Where more vapor or gas molecules are returning to the liquid state than are evaporating

Condensation nuclei Tiny particles such as tiny dust, smoke, soot, and salt crystals that are suspended in the air on which water condenses condensation point the temperature at which a gas or vapor changes back to a liquid

Condensation point the temperature at which a gas or vapor changes back to a liquid

Conduction The transfer of heat from a region of higher temperature to a region of lower temperature by increased kinetic energy moving from molecule to molecule

Constructive interference The condition in which two waves arriving at the same place, at the same time and in phase, add amplitudes to create a new wave

Control rods Rods inserted between fuel rods in a nuclear reactor to absorb neutrons and thus control the rate of the nuclear chain reaction

Convection Transfer of heat from a region of higher temperature to a region of lower temperature by the displacement of high-energy molecules-for example, the displacement of warmer, less dense air (higher kinetic energy) by cooler, denser air (lower kinetic energy)

Conventional current Opposite to electron current-that is, considers an electric current to consist of a drift of positive charges that flow from the positive terminal to the negative terminal of a battery

Coulomb Unit used to measure quantity of electric charge; equivalent to the charge resulting from the transfer of 6.24 billion particles such as the electron

Coulomb's law Relationship between charge, distance, and magnitude of the electrical force between two bodies

Covalent bond A chemical bond formed by the sharing of a pair of electrons

Covalent compound Chemical compound held together by a covalent bond or bonds

Crest The point of maximum positive displacement on a transverse wave is called a crest.

Critical angle Limit to the angle of incidence when all light rays are reflected internally

Critical mass Mass of fissionable material needed to sustain a chain reaction

Curvilinear Motion The motion of a body along a curved path is called curvilinear motion.

Cycle A complete vibration

De-acceleration See retardation

Decibel scale A nonlinear scale of loudness based on the ratio of the intensity level of a sound to the intensity at the threshold of hearing

Destructive interference The condition in which two waves arriving at the same point at the same time out of phase add amplitudes to create zero total disturbance. (also see constructive interference

Dew point temperature The temperature at which condensation begins

Dew Condensation of water vapor into droplets of liquid on surfaces

Diffraction The bending of light around the edge of an opaque object

Diffuse reflection Light rays reflected in many random directions, as opposed to the parallel rays reflected from a perfectly smooth surface such as a mirror

Direct current An electrical current that always moves in one direction

Direct proportion When two variables increase or decrease together in the same ratio (at the same rate)

Dispersion The effect of spreading colors of light into a spectrum with a material that has an index of refraction that varies with wavelength

Displacement The change in the position of an object in a particular direction is called displacement. Displacement may also be defined as the shortest distance between the initial and final position of a moving body. It is a vector quantity.

Distance The actual length of the path traveled by a body irrespective of the direction is called the distance traveled. It is a scalar quantity.

Doppler effect An apparent shift in the frequency of sound or light due to relative motion between the source of the sound or light and the observer

Echo A reflected sound that can be distinguished from the original sound, which usually arrives 0.1 sec or more after the original sound

Elastic strain An adjustment to stress in which materials recover their original shape after a stress is released

Electric circuit Consists of a voltage source that maintains an electrical potential, a continuous conducting path for a current to follow, and a device where work is done by the electrical potential; a switch in the circuit is used to complete or interrupt the conducting path

Electric current The flow of electric charge electric field force field produced by an electrical charge

Electric field lines A map of an electric field representing the direction of the force that a test charge would experience; the direction of an electric field shown by lines of force

Electric generator A mechanical device that uses wire loops rotating in a magnetic field to produce electromagnetic induction in order to generate electricity

Electric potential energy Potential energy due to the position of a charge near other charges

Electrical conductors Materials that have electrons that are free to move throughout the material; for example, metals

Electrical energy A form of energy from electromagnetic interactions; one of five forms of energy-mechanical, chemical, radiant, electrical, and nuclear

Electrical force A fundamental force that results from the interaction of electrical charge and is billions and billions of times stronger than the gravitational force; sometimes called the

Electrical insulators Electrical nonconductors, or materials that obstruct the flow of electric current

Electrical nonconductors Materials that have electrons that are not moved easily within the material-for example, rubber; electrical nonconductors are also called electrical insulators

Electrical resistance The property of opposing or reducing electric current

Electrolyte Water solution of ionic substances that conducts an electric current

Electromagnet A magnet formed by a solenoid that can be turned on and off by turning the current on and off

Electromagnetic force One of four fundamental forces; the force of attraction or repulsion between two charged particles

Electromagnetic induction Process in which current is induced by moving a loop of wire in a magnetic field or by changing the magnetic field

Electromagnetic waves The waves which are due to oscillating electrical and magnetic fields and do not need any material medium for their propagation are called electromagnetic waves. These waves can, however, travel through material medium also. Light waves, radio waves are examples of electromagnetic waves. All electromagnetic waves travel in vacuum with a speed of 3×10 8 m/s.

Electron configuration The arrangement of electrons in orbits and sub-orbits about the nucleus of an atom

Electron current Opposite to conventional current; that is, considers electric current to consist of a drift of negative charges that flows from the negative terminal to the positive terminal of a battery

Electron pair A pair of electrons with different spin quantum numbers that may occupy an orbital

Electron volt The energy gained by an electron moving across a potential difference of one volt; equivalent to 1.60 x 10^-19 Joules

Electron Subatomic particle that has the smallest negative charge possible and usually found in an orbital of an atom, but gained or lost when atoms become ions

Electronegativity The comparative ability of atoms of an element to attract bonding electrons

Electrostatic charge An accumulated electric charge on an object from a surplus or deficiency of electrons; also called

Element A pure chemical substance that cannot be broken down into anything simpler by chemical or physical means; there are over 100 known elements, the fundamental materials of which all matter is made

Energy The capacity of a body to do work is called its energy. Energy is a scalar quantity. The SI unit of energy is Joule.

Escape Velocity The minimum velocity with which an object must be thrown upwards so as to overcome the gravitational pull and escape into space, is called escape velocity (V esc ). The escape velocity depends upon the mass and radius of the planet/star. It does not depend upon the mass of the body thrown up. The escape velocity of earth is given by.

Evaporation Process of more molecules leaving a liquid for the gaseous state than returning from the gas to the liquid. It can occur at any given temperature from the surface of a liquid. Evaporation takes place only from the surface of the liquid. Evaporation causes cooling. Evaporation is faster if the surface of the liquid is large, the temperature is higher and the surrounding atmosphere does not contain a large amount of vapor of the liquid.

Fahrenheit scale of temperature On the Fahrenheit scale, the ice point, the ice point (lower fixed point) is taken as 32? F and the steam point (upper fixed point) is taken as 212 deg F. The interval between these two points is divided into 180 equal divisions. Thus, unit division on the Fahrenheit scale is 1deg F. The temperatures on the Celsius scale and the Fahrenheit scale are related by the relationship, C/100 = (F - 32) / 180. The temperature of a normal healthy person is 37 deg C or 98.6 deg F.

First law of motion Every object remains at rest or in a state of uniform straight-line motion unless acted on by an unbalanced force

Fluids Matter that has the ability to flow or be poured; the individual molecules of a fluid are able to move, rolling over or by one another

Force Force is a push or pull which tends to change the state of rest or of uniform motion , the direction of motion, or the shape and size of a body. Force is a vector quantity. The SI unit of force is Newton, denoted by N. One N is the force which when acts on a body of mass 1 kg produces an acceleration of 1 m/s².

Force of gravitation The force with which two objects attract each other by virtue of their masses is called the force of gravitation. The force of attraction acts even if the two objects are not connected to each other. It is an action-at-a-distance force.

Fracture strain An adjustment to stress in which materials crack or break as a result of the stress

Free fall The motion of a body towards the earth when no other force except the force of gravity acts on it is called free fall. All freely falling bodies are weightless.

Freezing point The temperature at which a phase change of liquid to solid takes place; the same temperature as the melting point for a given substance

Frequency (of waves) The number of waves produced per second is called its frequency.

Frequency (of oscillations) The number of oscillations made by an oscillating body per second is called the frequency.

Friction The force that resists the motion of one surface relative to another with which it is in contact. The cause of friction is that surfaces, however smooth they may look to the eye, on the microscopic scale have many humps and crests. Thus the actual area of contact is very small indeed, and the consequent very high pressure leads to local pressure welding of the surface. In motion the welds are broken and remade continually.

Fuel rod Long zirconium alloy tubes containing fissionable material for use in a nuclear reactor

Fundamental charge Smallest common charge known; the magnitude of the charge of an electron and a proton, which is 1.60 x 10^-19 coulomb

Fundamental frequency The lowest frequency (longest wavelength) that can set up standing waves in an air column or on a string

Fundamental properties A property that cannot be defined in simpler terms other than to describe how it is measured; the fundamental properties are length, mass, time, and charge

g Symbol representing the acceleration of an object in free fall due to the force of gravity; its magnitude is 9.80 m/sec^2 (32.0 ft/sec^2)

Gamma ray Very short wavelength electromagnetic radiation emitted by decaying nuclei

Gases A phase of matter composed of molecules that are relatively far apart moving freely in a constant, random motion and have weak cohesive forces acting between them, resulting in the characteristic indefinite shape and indefinite volume of a gas

Gram-atomic weight The mass in grams of one mole of an element that is numerically equal to its atomic weight

Gram-formula weight The mass in grams of one mole of a compound that is numerically equal to its formula weight

Gram-molecular weight The gram-formula weight of a molecular compound

Gravitational constant G The constant G which appears in the equation for Newton's law of gravitation is called the universal constant of gravitation or the gravitational constant. Numerically it is equal to the force of gravitation, which acts between two bodies of mass 1kg each separated by a distance of 1m. The value of G is 6.67×10-11 Nm²/kg².

Gravitational potential energy = mgh

Greenhouse effect The process of increasing the temperature of the lower parts of the atmosphere through redirecting energy back toward the surface; the absorption and reemission of infrared radiation by carbon dioxide, water vapor, and a few other gases in the atmosphere

Ground state Energy state of an atom with electrons at the lowest energy state possible for that atom

Half-life The time required for one-half of the unstable nuclei in a radioactive substance to decay into a new element

Heat Heat is a form of energy, which makes a body hot or cold. Heat is measured by the temperature-effect it produces in any material body. The SI unit of heat is Joule( J).

Heisenberg uncertainty principle You cannot measure both the exact momentum and the exact position of a subatomic particle at the same time-when the more exact of the two is known, the less certain you are of the value of the other

Hertz Unit of frequency; equivalent to one cycle per second

Horsepower Measurement of power defined as a power rating of 550 ft-lb/sec

Hypothesis A tentative explanation of a phenomenon that is compatible with the data and provides a framework for understanding and describing that phenomenon

Ice-point It is the melting point of pure melting ice under 1 atm pressure. The ice point is taken as the lower fixed point ( 0 deg C or 32 deg F ) for temperature scales.

Impulse The impulse acting on a body is equal to the product of the force acting on the body and the time for which it acts. If the force is variable, the impulse is the integral of Fdt from t0 to t1. The impulse of a force acting for a given time interval is equal to change in momentum produced over that interval. J=m(v-u), assuming that the mass m remains constant while the velocity changes from v to u. The SI units of impulse are kg m/s.

Impulsive force The force which acts on a body for a very short time but produces a large change in the momentum of the body is called an impulsive force.

Incandescent Matter emitting visible light as a result of high temperature for example, a light bulb, a flame from any burning source, and the sun are all incandescent sources because of high temperature

Incident ray Line representing the direction of motion of incoming light approaching a boundary

Index of refraction The ratio of the speed of light in a vacuum to the speed of light in a material

Inertia The property of matter that causes it to resist any change in its state of rest or of uniform motion. There are three kinds of inertia- inertia of rest, inertia of motion and inertia of direction. The mass of a body is a measure of its inertia.

Infrasonic Sound waves having too low a frequency to be heard by the human ear; sound having a frequency of less than 20 Hz

Insulators Materials that are poor conductors of heat-for example, heat flows slowly through materials with air pockets because the molecules making up air are far apart; also, materials that are poor conductors of electricity, for example, glass or wood

Intensity A measure of the energy carried by a wave

Interference Phenomenon of light where the relative phase difference between two light waves produces light or dark spots, a result of light's wavelike nature

Intermolecular forces Forces of interaction between molecules

Internal energy Sum of all the potential energy and all the kinetic energy of all the molecules of an object

Inverse proportion The relationship in which the value of one variable increases while the value of the second variable decreases at the same rate (in the same ratio)

Ionization Process of forming ions from molecules

Ionized An atom or a particle that has a net charge because it has gained or lost electrons

Isostasy A balance or equilibrium between adjacent blocks of crust

Isotope Atoms of an element with identical chemical properties but with different masses; isotopes are atoms of the same element with different numbers of neutrons

Joule Metric unit used to measure work and energy; can also be used to measure heat; equivalent to newton-meter

Kelvin scale of temperature On this scale, the ice-point (the lower fixed point) is taken as 273.15K and the (the upper fixed point) is taken as 373.15K. The interval between these two points is divided into 100 equal parts. Each division is equal to 1K.

Kepler's first law Relationship in planetary motion that each planet moves in an elliptical orbit, with the sun located at one focus

Kepler's laws of planetary motion The three laws describing the motion of the planets

Kepler's second law Relationship in planetary motion that an imaginary line between the sun and a planet moves over equal areas of the ellipse during equal time intervals

Kepler's third law Relationship in planetary motion that the square of the period of an orbit is directly proportional to the cube of the radius of the major axis of the orbit

Kilocalorie The amount of energy required to increase the temperature of one kilogram of water one degree Celsius: equivalent to 1,000 calories

Kilogram The fundamental unit of mass in the metric system of measurement

Kinetic Energy Energy possessed by a body by the virtue of its motion is called kinetic energy. Kinetic energy = 1/2 m v²

Latent heat of evaporization The heat absorbed when one gram of a substance changes from the liquid phase to the gaseous phase, or the heat released when one gram of gas changes from the gaseous phase to the liquid phase

Latent heat of fusion The quantity of heat required to convert one unit mass of a substance from solid to the liquid state at its melting point (without any change in its temperature) is called its latent heat of fusion (L). The SI unit of latent heat of fusion is J kg-1.

Latent heat Refers to the heat hidden in phase changes

Law of Conservation of Energy The change of one form of energy into another is called transformation of energy. For example, when a body falls its potential energy is converted to kinetic energy.

Law of conservation of mass Same as law of conservation of matter; mass, including single atoms, is neither created nor destroyed in a chemical reaction