1. Angle of reflection Angle of a reflected ray or particle from a surface; measured
from a line perpendicular to the surface (the normal)
2. 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.
3. 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.
4. 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
5. Angular Velocity The rate of change of angular displacement is called angular
velocity.
6. Astronomical unit The radius of the earth's orbit is defined as one astronomical
7. unit (A.U.)
8. Atom The smallest unit of an element that can exist alone or in combination with
other elements
9. 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
10. Atomic number The number of protons in the nucleus of an atom
11. 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
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
13. Axis The imaginary line about which a planet or other object rotates
14. Background Radiation Ionizing radiation (alpha, beta, gamma, etc.) from natural
sources
15. 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.
16. 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
17. Barometer An instrument that measures atmospheric pressure, used in weather
forecasting and in determining elevation above sea level
18. Beat Rhythmic increases and decreases of volume from constructive and
destructive interference between two sound waves of slightly different
frequencies
19. Beta particle High-energy electron emitted as ionizing radiation from a decaying
nucleus; also known as a beta ray
20. Big bang theory Current model of galactic evolution in which the universe was
created from an intense and brilliant explosion from a primeval fireball
21. 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
22. Black hole The theoretical remaining core of a supernova that is so dense that
even light cannot escape
23. Blackbody radiation Electromagnetic radiation emitted by an ideal material (the
blackbody) that perfectly absorbs and perfectly emits radiation
24. 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
25. 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
26. Boundary The division between two regions of differing physical properties
27. British thermal unit The amount of energy or heat needed to increase the
temperature of one pound of water one degree Fahrenheit (abbreviated Btu)
28. Cathode rays Negatively charged particles (electrons) that are emitted from a
negative terminal in an evacuated glass tube
29. 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.
30. Centigrade Alternate name for the Celsius scale
31. 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
32. Centripetal force The force required to pull an object out of its natural straight-line
path and into a circular path; centripetal means
33. 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
34. Circular Motion The motion of a body along a circular path is called circular
motion.
35. 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.
36. 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.
37. 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.
38. Compressive stress A force that tends to compress the surface as the earth's
plates move into each other
39. Condensation (sound) A compression of gas molecules; a pulse of increased
density and pressure that moves through the air at the speed of sound
40. Condensation (water vapor) Where more vapor or gas molecules are returning to
the liquid state than are evaporating
41. 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
42. Condensation point the temperature at which a gas or vapor changes back to a
liquid
43. 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
44. 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
45. Control rods Rods inserted between fuel rods in a nuclear reactor to absorb
neutrons and thus control the rate of the nuclear chain reaction
46. 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)
47. 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
48. 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
49. Coulomb's law Relationship between charge, distance, and magnitude of the
electrical force between two bodies
50. Covalent bond A chemical bond formed by the sharing of a pair of electrons
51. Covalent compound Chemical compound held together by a covalent bond or
bonds
52. Crest The point of maximum positive displacement on a transverse wave is
called a crest.
53. Critical angle Limit to the angle of incidence when all light rays are reflected
internally
54. Critical mass Mass of fissionable material needed to sustain a chain reaction
55. Curvilinear Motion The motion of a body along a curved path is called curvilinear
motion.
56. Cycle A complete vibration
57. De-acceleration See retardation
58. 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
59. 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
60. Dew point temperature The temperature at which condensation begins
61. Dew Condensation of water vapor into droplets of liquid on surfaces
62. Diffraction The bending of light around the edge of an opaque object
63. 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
64. Direct current An electrical current that always moves in one direction
65. Direct proportion When two variables increase or decrease together in the same
ratio (at the same rate)
66. Dispersion The effect of spreading colors of light into a spectrum with a material
that has an index of refraction that varies with wavelength
67. 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.
68. 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.
69. 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
70. Echo A reflected sound that can be distinguished from the original sound, which
usually arrives 0.1 sec or more after the original sound
71. Elastic strain An adjustment to stress in which materials recover their original
shape after a stress is released
72. 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
73. Electric current The flow of electric charge electric field force field produced by an
electrical charge
74. 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
75. Electric generator A mechanical device that uses wire loops rotating in a
magnetic field to produce electromagnetic induction in order to generate
electricity
76. Electric potential energy Potential energy due to the position of a charge near
other charges
77. Electrical conductors Materials that have electrons that are free to move
throughout the material; for example, metals
78. Electrical energy A form of energy from electromagnetic interactions; one of five
forms of energy-mechanical, chemical, radiant, electrical, and nuclear
79. 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
80. Electrical insulators Electrical nonconductors, or materials that obstruct the flow
of electric current
81. Electrical nonconductors Materials that have electrons that are not moved easily
within the material-for example, rubber; electrical nonconductors are also called
electrical insulators
82. Electrical resistance The property of opposing or reducing electric current
83. Electrolyte Water solution of ionic substances that conducts an electric current
84. Electromagnet A magnet formed by a solenoid that can be turned on and off by
turning the current on and off
85. Electromagnetic force One of four fundamental forces; the force of attraction or
repulsion between two charged particles
86. Electromagnetic induction Process in which current is induced by moving a loop
of wire in a magnetic field or by changing the magnetic field
87. 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.
88. Electron configuration The arrangement of electrons in orbits and sub-orbits
about the nucleus of an atom
89. 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
90. Electron pair A pair of electrons with different spin quantum numbers that may
occupy an orbital
91. Electron volt The energy gained by an electron moving across a potential
difference of one volt; equivalent to 1.60 x 10^-19 Joules
92. 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
93. Electronegativity The comparative ability of atoms of an element to attract
bonding electrons
94. Electrostatic charge An accumulated electric charge on an object from a surplus
or deficiency of electrons; also called
95. 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
96. 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.
97. 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.
98. 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.
99. 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.
100. First law of motion Every object remains at rest or in a state of uniform straightline
motion unless acted on by an unbalanced force
101. 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
102. 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.
103. 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.
104. Fracture strain An adjustment to stress in which materials crack or break as a
result of the stress
105. 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.
106. 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
107. Frequency (of waves) The number of waves produced per second is called its
frequency.
108. Frequency (of oscillations) The number of oscillations made by an oscillating
body per second is called the frequency.
109. 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.
110. Fuel rod Long zirconium alloy tubes containing fissionable material for usein a
nuclear reactor
111. 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
112. Fundamental frequency The lowest frequency (longest wavelength) thatcan set
up standing waves in an air column or on a string
113. 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
114. 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)
115. Gamma ray Very short wavelength electromagnetic radiation emitted by
decaying nuclei
116. 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
117. Gram-atomic weight The mass in grams of one mole of an element that is
numerically equal to its atomic weight
118. Gram-formula weight The mass in grams of one mole of a compound that is
numerically equal to its formula weight
119. Gram-molecular weight The gram-formula weight of a molecular compound
120. 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.
121. Gravitational potential energy = mgh
122. 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
123. Ground state Energy state of an atom with electrons at the lowest energy state
possible for that atom
124. Half-life The time required for one-half of the unstable nuclei in a radioactive
substance to decay into a new element
125. 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).
126. 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
127. Hertz Unit of frequency; equivalent to one cycle per second
128. Horsepower Measurement of power defined as a power rating of 550 ft-lb/sec
129. Hypothesis A tentative explanation of a phenomenon that is compatible with the
data and provides a framework for understanding and describing that
phenomenon
130. 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.
131. 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.
132. 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.
133. 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
134. Incident ray Line representing the direction of motion of incoming light
approaching a boundary
135. Index of refraction The ratio of the speed of light in a vacuum to the speed of light
in a material
136. 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.
137. Infrasonic Sound waves having too low a frequency to be heard by the human
ear; sound having a frequency of less than 20 Hz
138. 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
139. Intensity A measure of the energy carried by a wave
140. 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
141. Intermolecular forces Forces of interaction between molecules
142. Internal energy Sum of all the potential energy and all the kinetic energy of all the
molecules of an object
143. 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)
144. Ionization Process of forming ions from molecules
145. 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
146. 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
147. Joule Metric unit used to measure work and energy; can also be used to
measure heat; equivalent to newton-meter
148. 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.
149. Kepler's first law Relationship in planetary motion that each planet moves in an
elliptical orbit, with the sun located at one focus
150. Kepler's laws of planetary motion The three laws describing the motion of the
planets
151. 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
152. 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
153. Kilocalorie The amount of energy required to increase the temperature of one
kilogram of water one degree Celsius: equivalent to 1,000 calories
154. Kilogram The fundamental unit of mass in the metric system of measurement
155. Kinetic Energy Energy possessed by a body by the virtue of its motion is called
kinetic energy. Kinetic energy = 1/2 m v²
