SAT Physics Subject Test Glossary:
A
Absolute zero: The lowest theoretical temperature a material can have, where the molecules that make up the material have no kinetic energy. Absolute zero is reached at 0 K or –273o C.
Acceleration: A vector quantity defined as the rate of change of the velocity vector with time.
Activity: In radioactive substances, the number of nuclei that decay per second. Activity, A, will be larger in large samples of radioactive material since there will be more nuclei.
Alpha decay: A form of radioactive decay where a heavy element emits an alpha particle and some energy, thus transforming into a lighter, more stable, element.
Alpha particle: A particle, which consists of two protons and two neutrons. It is identical to the nucleus of a helium atom and is ejected by heavy particles undergoing alpha decay.
Amplitude: In reference to oscillation, the amplitude is the maximum displacement of the oscillator from its equilibrium position. Amplitude tells how far an oscillator is swinging back and forth. In the periodic motion, the amplitude is the maximum displacement in each cycle of a system in periodic motion. The precise definition of amplitude depends on the particular situation: in the case of a stretched string, it would be measured in meters, whereas for sound waves it would be measured in units of pressure.
Angle of Incidence: When a light ray strikes a surface, the angle of incidence is the angle between the incident ray and the normal.
Angle of reflection: The angle between a reflected ray and the normal.
Angle of refraction: The angle between a refracted ray and the line normal to the surface.
Angular acceleration: A vector quantity, equal to the rate of change of the angular velocity vector with time. It is typically given in units of rad/s2.
Angular displacement: The net change, in a point’s angular position, It is a scalar quantity.
Angular frequency: A frequency, f, defined as the number of revolutions a rigid body makes in a given time interval. It is a scalar quantity commonly denoted in units of Hertz (Hz) or s–1.
Angular momentum: A vector quantity, L, that is the rotational analogue of linear momentum. For a single particle, the angular momentum is the cross product of the particle’s displacement from the axis of rotation and the particle’s linear momentum, For a rigid body, the angular momentum is a product of the object’s moment of inertia, I, and its angular velocity.
Angular period: The time, T, required for a rigid body to complete one revolution.
Angular position: The position, of an object according to a co-ordinate system measured in s of the angle of the object from a certain origin axis. Conventionally, this origin axis is the positive x-axis.
Angular velocity: A vector quantity, that reflects the change of angular displacement with time, and is typically given in units of rad/s. To find the direction of the angular velocity vector, take your right hand and curl your fingers along the particle or body’s direction of rotation. Your thumb then points in the direction of the body’s angular velocity.
Antinode: The points midway between nodes on a standing wave, where the oscillations are largest.
Atom: The building blocks of all matter, atoms are made up of a nucleus consisting of protons and neutrons, and a number of electrons that orbit the nucleus. An electrically neutral atom has as many protons as it has electrons.
Atomic number: A number, Z, associated with the number of protons in the nucleus of an atom. Every element can be defined in s of its atomic number since every atom of a given element has the same number of protons.
Axis of rotation: The line that every particle in the rotating rigid body circles about.
B
Basis vector: A vector of magnitude 1 along one of the coordinate axes. Generally, we take the basis vectors to be and, the vectors of length 1 along the x- and y-axes, respectively.
Beats: When two waves of slightly different frequencies interfere with one another, they produce a “beating” interference pattern that alternates between constructive (in-phase) and destructive (out-of-phase). In the case of sound waves, this sort of interference makes a “we-we-we” sound, and the frequency of the beats is equal to the difference in the frequencies of the two interfering waves.
Beta decay: A form of radioactive decay where a heavy element ejects a beta particle and a neutrino, becoming a lighter element in the process.
Beta particle: A particle, identical to an electron. Beta particles are ejected from an atom in the process of beta decay.
Bohr atomic model: A model for the atom developed in 1913 by Niels Bohr. According to this model, the electrons orbiting a nucleus can only orbit at certain particular radii. Excited electrons may jump to a more distant radius and then return to their ground state, emitting a photon in the process.
Boiling point: The temperature at which a material will change phase from liquid to gas or gas to liquid.
Boyle’s Law: For a gas held at a constant temperature, pressure and volume are inversely proportional.
C
Calorie: The amount of heat needed to raise the temperature of one gram of water by one degree Celsius.1 cal = 4.19 J.
Celsius: A scale for measuring temperature, defined such that water freezes at 0 o C and boils at 100oC.0oC = 273 K.
Center of curvature: With spherical mirrors, the centre of the sphere of which the mirror is a part. All of the normals pass through it.
Center of mass: Given the trajectory of an object or system, the centre of mass is the point that has the same acceleration as the object or system as a whole would have if its mass were concentrated at that point. In terms of force, the centre of mass is the point at which a given net force acting on a system will produce the same acceleration as if the system’s mass were concentrated at that point.
Centripetal acceleration: The acceleration of a body experiencing uniform circular motion. This acceleration is always directed toward the centre of the circle. Centripetal force. The force necessary to maintain a body in uniform circular motion. This force is always directed radially toward the centre of the circle.
Chain reaction: The particles and energy released by the fission or fusion of one atom may trigger the fission or fusion of further atoms. In a chain reaction, fission or fusion is rapidly transferred to a large number of atoms, releasing tremendous amounts of energy.
Charles’s Law: For a gas held at constant pressure, temperature and volume are directly proportional.
The coefficient of kinetic friction: The coefficient of kinetic friction, , for two materials is the constant of proportionality between the normal force and the force of kinetic friction. It is always a number between zero and one.
The coefficient of linear expansion: A coefficient that tells how much a material will expand or contract lengthwise when it is heated or cooled.
The coefficient of static friction: The coefficient of static friction, for two materials, is the constant of proportionality between the normal force and the maximum force of static friction. It is always a number between zero and one.
The coefficient of volume expansion: A coefficient that tells how much the volume of a solid will change when it is heated or cooled.
Coherent light: Light such that all of the associated waves have the same wavelength and are in phase.
Collision: When objects collide, each object feels a force for a short amount of time. This force imparts an impulse or changes the momentum of each of the colliding objects. The momentum of a system is conserved in all kinds of collisions. Kinetic energy is conserved in elastic collisions, but not in inelastic collisions. In a perfectly inelastic collision, the colliding objects stick together after they collide.
Completely inelastic collision: A collision in which the colliding particles stick together.
Component: Any vector can be expressed as the sum of two mutually perpendicular component vectors. Usually, but not always, these components are multiples of the basis vectors, and; that is, vectors along the x-axis and y-axis. We define these two vectors as the x-and y-components of the vector.
Compression: An area of high air pressure that acts as the wave crest for sound waves. The spacing between successive compressions is the wavelength of sound, and the number of successive areas of compression that arrive at the ear per second is the frequency, or pitch, of the sound.
Concave lens: Also called a diverging lens, a lens that is thinner in the middle than at the edges. Concave lenses refract light away from a focal point.
Concave mirror: A mirror that is curved such that its centre is farther from the viewer than the edges, such as the front of a spoon. Concave mirrors reflect light through a focal point.
Conduction: Heat transfer by molecular collisions.
Conservation of Angular Momentum: If the net torque acting on a rigid body is zero, then the angular momentum of the body is constant or conserved.
Conservation of momentum: The principle stating that for any isolated system, linear momentum is constant with time.
Constant of proportionality: A constant in the numerator of a formula.
Constructive interference: The amplification of one wave by another, the identical wave of the same sign. Two constructively interfering waves are said to be “in phase.”
Convection: Heat transfer via the mass movement of molecules.
Convex lens: Also called a converging lens, a lens that is thicker in the middle than at the edges. Convex lenses refract light through a focal point.
Convex mirror: A mirror that is curved such that its centre is closer to the viewer than the edges, such as a doorknob. Convex mirrors reflect light away from a focal point.
Cosine: The cosine of an angle in a right triangle is equal to the length of the side adjacent to the angle divided by the length of the hypotenuse.
Crest: The points of maximum displacement along a wave. In travelling waves, the crests move in the direction of propagation of the wave. The crests of standing waves also called anti-nodes, remain in one place.
Critical angle: For two given media, the smallest angle of incidence at which total internal reflection occurs.
Cross product: A form of vector multiplication, where two vectors are multiplied to produce a third vector. The cross product of two vectors, A and B, separated by an angle, is , where is a unit vector perpendicular to both A and B. To define which direction points, you must use the right-hand rule.
Cycle: In oscillation, a cycle occurs when an object undergoing oscillatory motion completes a “round-trip.” For instance, a pendulum bob released at the angle has completed one cycle when it swings to and then back to again. In the period motion, a cycle is a sequence through which a system once during each oscillation. A cycle can consist of one trip up and down for a piece of stretched string, or of a compression followed by a rarefaction of air pressure for sound waves.
D
De Broglie wavelength: A wavelength, given by = h /mv, which is associated with matter. Louis de Broglie proposed the idea that matter could be treated as waves in 1923 and applied this theory successfully to small particles like electrons. Decay constant A constant, not to be confused with wavelength, that defines the speed at which a radioactive element undergoes decay. The greater is, the faster the element decays.
Decibel: A logarithmic unit for measuring the volume of sound, which is the square of the amplitude of sound waves.
Deposition: The process by which a gas turns directly into a solid because it cannot exist as a liquid at certain pressures.
Destructive interference: The cancellation of one wave by another wave that is exactly out of phase with the first. Despite the dramatic name of this phenomenon, nothing is “destroyed” by this interference—the two waves emerge intact once they have passed each other.
Diffraction: The bending of light at the corners of objects or as it passes through narrow slits or apertures.
Diffraction grating: A sheet, film, or screen with a pattern of equally spaced slits. Typically the width of the slits and space between them is chosen to generate a particular diffraction pattern.
Direction: The property of a vector that distinguishes it from a scalar: while scalars have only a magnitude, vectors have both a magnitude and a direction. When graphing vectors in the XY-coordinate space, the direction is usually given by the angle measured counterclockwise from the x-axis to the vector.
Directly proportional: Two quantities are directly proportional if an increase in one results in a proportional increase in the other, and a decrease in one results in a proportional decrease in the other. In a formula defining a certain quantity, those quantities to which it's directly proportional will appear in the numerator.
Dispersion: The separation of different colour light via refraction.
Displacement: A vector quantity, commonly denoted by the vector s, which reflects an object’s change in spatial position. The displacement vector points from the object’s starting position to the object’s current position in space. If an object is moved from point A to point B in space along the path the magnitude of the object’s displacement is the separation of points A and B. Note that the path an object takes to get from point A to point B does not figure when dealing displacement.
Distance: A B, A scalar quantity. If an object is moved from point A to point B space along path AB, the distance that the object has travelled is the length of the path AB. Distance is to be contrasted with displacement, which is simply a measure of the distance between points A and B and doesn’t take into account the path followed between A and B.
Doppler shift: Waves produced by a source that is moving with respect to the observer will seem to have a higher frequency and smaller wavelength if the motion is towards the observer, and a lower frequency and longer wavelength if the motion is away from the observer. The speed of the waves is independent of the motion of the source.
Dot product: A form of vector multiplication, where two vectors are multiplied to produce a scalar. The dot product of two vectors, A and B, is expressed by the equation A · B = AB cos.
Dynamics: The application of kinematics to understand why objects move the way they do. More precisely, dynamics is the study of how forces cause motion.
E
Efficiency: For a heat engine, the ratio of work done by the engine to heat intake. Efficiency is never 100%.
Elastic collision: A collision in which both kinetic energy and momentum are conserved.
Electric generator: A device that converts mechanical energy into electrical energy by rotating a coil in a magnetic field; sometimes called a “dynamo”.
Electromagnetic induction: The property by which a charge moving in a magnetic field creates an electric field.
Electromagnetic spectrum: The spectrum containing all the different kinds of electromagnetic waves, ranging in wavelength and frequency.
Electromagnetic wave: A transverse travelling wave created by the oscillations of an electric field and a magnetic field. Electromagnetic waves travel at the speed of light, m/s. Examples include microwaves, X rays, and visible light.
Electron: A negatively charged particle that orbits the nucleus of the atom.
Electronvolt: A unit of measurement for energy on atomic levels. 1 eV = J.
Energy: A conserved scalar quantity associated with the state or condition of an object or system of objects. We can roughly define energy as the capacity of an object or system to do work. There are many different types of energy, such as kinetic energy, potential energy, thermal energy, chemical energy, mechanical energy, and electrical energy.
Entropy: The disorder of a system.
Equilibrium: The state of a nonrotating object upon whom the net torque acting is zero.
Equilibrium position: The stable position of a system where the net force acting on the object is zero.
F
Faraday’s Law: A law, | | =, which states that the induced emf is the change in magnetic flux in a certain time.
First Law of Thermodynamics: Essentially a restatement of energy conservation, it states that the change in the internal energy of a system is equal to the heat added plus the work is done on the system.
Focal length: The distance between the focal point and the vertex of a mirror or lens. For concave mirrors and convex lenses, this number is positive. For convex mirrors and concave lenses, this number is negative.
Focal point: The point of a mirror or lens where all light that runs parallel to the principal axis will be focused. Concave mirrors and convex lenses are designed to focus light into the focal point. Convex mirrors and concave lenses focus light away from the focal point.
Force: A push or a pull that causes an object to accelerate.
Free-body diagram: Illustrates the forces acting on an object, drawn as vectors originating from the centre of the object.
Frequency: The number of cycles executed by a system in one second. Frequency is the inverse of period, f= 1/T. Frequency is measured in hertz, Hz.
Frictional force: A force caused by the roughness of two materials in contact, deformations in the materials, and a molecular attraction between the materials. Frictional forces are always parallel to the plane of contact between two surfaces and opposite the direction that the object is being pushed or pulled.
Fundamental: The standing wave with the lowest frequency that is supported by a string with both ends tied down is called the fundamental, or resonance, of the string. The wavelength of the fundamental is twice the length of the string,
G
Gamma decay: A form of radioactivity where an excited atom releases a photon of gamma radiation, thereby returning to a lower energy state. The atomic structure itself does not change in the course of gamma radiation.
Gamma ray: An electromagnetic wave of very high frequency.
Gold foil experiment: An experiment by Ernest Rutherford that proved for the first time that atoms have nuclei.
Gravitational constant: The constant of proportionality in Newton’s Law of Gravitation. It reflects the proportion of the gravitational force and, the product of two particles’ masses divided by the square of the bodies’ separation. N · m2/kg2.
Gravitational Potential Energy: The energy associated with the configuration of bodies attracted to each other by the gravitational force. It is a measure of the amount of work necessary to get the two bodies from a chosen point of reference to their present position. This point of reference is usually chosen to be a point of infinite distance, giving the equation. Objects of mass m that are a height h above the surface of the earth have a gravitational potential energy of.
Ground state: In the Bohr model of the atom, the state in which an electron has the least energy and orbits closest to the nucleus.
H
Half-life: The amount of time it takes for one-half of a radioactive sample to decay.
Harmonic series: The series of standing waves supported by a string with both ends tied down. The first member of the series, called the fundamental, has two nodes at the ends and one anti-node in the middle. The higher harmonics are generated by placing an integral number of nodes at even intervals over the length of the string. The harmonic series is very important in music.
Heat: A transfer of thermal energy. We don’t speak about systems “having” heat, but about their “transferring” heat, much in the way that dynamical systems don’t “have” work, but rather “do” work.
Heat engine: A machine that operates by taking heat from a hot place, doing some work with that heat, and then exhausting the rest of the heat into a cool place. The internal combustion engine of a car is an example of a heat engine. Heat transfer A transfer of thermal energy from one system to another.
Hertz (Hz): The units of frequency, defined as inverse-seconds (1 Hz = 1 s–1). “Hertz” can be used interchangeably with “cycles per second.”
Hooke’s Law: For an oscillating spring, the restoring force exerted by the spring is directly proportional to the displacement. That is, the more the spring is displaced, the stronger the force that will pull toward the equilibrium position. This law is expressed mathematically as F = –kx, where F is the restoring force and x is the displacement. The constant of proportionality, –k, is the spring constant.
Hypotenuse: The longest side of a right triangle, opposite to the right angle.
I
Ideal gas law: An equation, P V = n R T, that relates the pressure, volume, temperature, and quantity of an ideal gas. An ideal gas is one that obeys the approximations laid out in the kinetic theory of gases.
Impulse: A vector quantity defined as the product of the force acting on a body multiplied by the time interval over which the force is exerted.
Incident ray: When dealing with reflection or refraction, the incident ray is the ray of light before it strikes the reflecting or refracting surface.
Inclined plane: A wedge or a slide. The dynamics of objects sliding down inclined planes is a popular topic on SAT II Physics.
Index of refraction: The index of refraction n = c / v of a substance characterizes the speed of light in that substance,v. It also characterizes, by way of Snell's Law, the angle at which light refracts in that substance.
Induced current: The current induced in a circuit by a change in magnetic flux.
Inelastic collision: A collision in which momentum is conserved but kinetic energy is not.
Inertia: The tendency of an object to remain at a constant velocity or its resistance to being accelerated. Newton’s First Law is alternatively called the Law of Inertia because it describes this tendency.
Inertial reference frame: A reference frame in which Newton’s First Law is true. Two inertial reference frames move at a constant velocity relative to one another. According to the first postulate of Einstein’s theory of special relativity, the laws of physics are the same in all inertial reference frames.
Instantaneous velocity: The velocity at any given instant in time. To be contrasted with average velocity, which is a measure of the change in displacement over a given time interval.
Internal energy: The energy stored in a thermodynamic system.
Inversely proportional: Two quantities are inversely proportional if an increase in one results in a proportional decrease in the other, and a decrease in one results in a proportional increase in the other. In a formula defining a certain quantity, those quantities to which it's inversely proportional will appear in the denominator.
Isolated system: A system that no external net force acts upon. Objects within the system may exert forces upon one another, but they cannot receive any impulse from outside forces. Momentum is conserved in isolated systems.
Isotope: 7Atoms of the same element may have different numbers of neutrons and therefore different masses. Atoms of the same element but with different numbers of neutrons are called isotopes of the same element.
J
Joule: The joule(J) is the unit of work and energy. A joule is 1 N·m or 1 kg · m2/s2.
K
Kelvin: A scale for measuring temperature, defined such that theoretical temperature a material can have. 273K = 00c
Kepler’s First Law: The path of each planet around the sun is an ellipse with the sun at one focus.
Kepler’s Second Law: If a line is drawn from the sun to the planet, then the area swept out by this line in a given time interval is constant.
Kepler’s Third Law: Given the period, T, and semi-major axis, a, of a planet’s orbit, the ratio is the same for every planet. Kinematic equations 0K is the lowest 0oC. The five equations used to solve problems in kinematics in one dimension with uniform acceleration.
Kinematics: Kinematics is the study and description of the motion of objects.
Kinetic energy: Energy associated with the state of motion. The translational kinetic energy of an object is given by the equation.
Kinetic friction: The force between two surfaces moving relative to one another. The frictional force is parallel to the plane of contact between the two objects and in the opposite direction of the sliding object’s motion.
Kinetic theory of gases: A rough approximation of how gases work, that is quite accurate in everyday conditions. According to the kinetic theory, gases are made up of tiny, round molecules that move about in accordance with Newton’s Laws, and collide with one another and other objects elastically. We can derive the ideal gas law from the kinetic theory.
L
Latent heat of fusion: The amount of heat necessary to transform a solid at a given temperature into a liquid of the same temperature, or the amount of heat needed to be removed from a liquid of a given temperature to transform it into a solid of the same temperature.
Latent heat of sublimation: The amount of heat necessary for a material undergoing sublimation to make a phase change from gas to solid or solid to gas, without a change in temperature.
Latent heat of transformation: The amount heat necessary to cause a substance to undergo a phase transition.
Latent heat of vaporization: The amount of heat necessary to transform a liquid at a given temperature into a gas of the same temperature, or the amount of heat needed to be taken away from a gas of a given temperature to transform it into a liquid of the same temperature.
Law of conservation of energy: Energy cannot be made or destroyed; energy can only be changed from one place to another or from one form to another.
Law of reflection: For a reflected light ray, . In other words, a ray of light reflects of a surface in the same plane as the incident ray and the normal, and at an angle to the normal that is equal to the angle between the incident ray and the normal.
Legs: The two shorter sides of a right triangle that meet at the right angle. Lenz’s Law States that the current induced in a circuit by a change in magnetic flux is in the direction that will oppose that change in flux. Using the right-hand rule, point your thumb in the opposite direction of the change in magnetic flux. The direction your fingers curl into a fist indicates the direction of the current.
Longitudinal waves: Waves that oscillate in the same direction as the propagation of the wave. The sound is carried by longitudinal waves since the air molecules move back and forth in the same direction the sound travels.
Loudness: The square of the amplitude of a sound wave is called the sound’s loudness, or volume.
M
Magnetic flux: The dot product of the area and the magnetic field passing through it. Graphically, it is a measure of the number and length of magnetic field lines passing through that area. It is measured in Webers (Wb).
Magnification: The ratio of the size of the image produced by a mirror or lens to the size of the original object. This number is negative if the image is upside-down.
Magnitude: A property common to both vectors and scalars. In the graphical representation of a vector, the vector’s magnitude is equal to the length of the arrow.
The Margin of error: The amount of error that’s possible in a given measurement.
Mass: A measurement of a body’s inertia, or resistance to being accelerated.
Mass defect: The mass difference between a nucleus and the sum of the masses of the constituent protons and neutrons.
Mass number: The mass number, A, is the sum of the number of protons and neutrons in a nucleus. It is very close to the weight of that nucleus in atomic mass units.
Maxima: In an interference or diffraction pattern, the places where there is the most light.
Mechanical energy: The sum of a system’s potential and kinetic energy. In many systems, including projectiles, pulleys, pendulums, and motion on frictionless surfaces, mechanical energy is conserved. One important type of problem in which mechanical energy is not conserved is the class of problems involving friction.
Medium: The substance that is displaced as a wave propagates through it. Air is the medium for sound waves, the string is the medium of transverse waves on a string, and water is the medium for ocean waves. Note that even if the waves in a given medium travel great distances, the medium itself remains more or less in the same place.
Melting point: The temperature at which a material will change phase from solid to liquid or liquid to solid.
Meson: A class of elementary particle whose mass is between that of a proton and that of an electron. A common kind of meson is the pion.
Michelson-Morley experiment: An experiment in 1879 that showed that the speed of light is constant to all observers. Einstein used the results of this experiment as support for his theory of special relativity.
Minima: In an interference or diffraction pattern, the places where there is the least light.Mole The number of hydrogen atoms in one gram of hydrogen, equal to 6.023×1023. When counting the number of molecules in a gas, it is often convenient to count them in moles.
Moment of inertia: A rigid body’s resistance to being rotated. The moment of inertia for a single particle is MR2, where M is the mass of the rigid body and R is the distance to the rotation axis. For rigid bodies, calculating the moment of inertia is more complicated, but it generally takes the form of a constant multiplied by MR2.
Momentum: Linear momentum, p, commonly called “momentum” for short, is a vector quantity defined as the product of an object’s mass, m, and its velocity, v.
Motional emf: The emf created by the motion of a charge through a magnetic field. Mutual Induction. The property by which a changing current in one coil of wire induces an emf in another.
N
Neutrino: An almost massless particle of neutral charge that is released along with a beta particle in beta decay.
Neutron: A neutrally charged particle that, along with protons, constitutes the nucleus of an atom.
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