## SAT Subject Test Physics (2012)

### GLOSSARY

**absolute zero** the lowest possible temperature at which all molecular motion would cease; 0 K

**acceleration** a change in velocity divided by the time required for the change to occur

**alpha decay** the spontaneous emission of an alpha particle, which is a helium nucleus, by certain radioactive substances

**ammeter** a device used to measure current

**amplitude** the maximum displacement of the particles of a medium

**angular acceleration** the rate of change in angular velocity over time

**angular displacement** a vector measure of the rotation of an object about an axis

**angular momentum** the product of the mass, velocity, and radius of motion

**angular velocity** the rate of change of angular displacement with respect to time

**Archimedes’ Principle** the rule stating that an object immersed in a fluid will experience a buoyant force equal to the weight of the fluid it displaces

**atomic number** the number of protons in the nucleus of an atom

**average speed** the total distance an object travels divided by the time during which it traveled that distance

**average velocity** the total change in displacement divided by the time during which the displacement occurred

**balanced forces** a combination of forces on an object that result in a net force of zero

**beat** the interference caused by two sets of sound waves with only slightly different frequencies

**Bernoulli’s Principle** the rule stating that as the speed of a moving fluid increases, the pressure exerted within the fluid decreases

**beta decay** the spontaneous emission of an electron or a positron by certain radioactive substances

**binding energy** the energy required to break apart an atomic nucleus; the difference in energy between the nucleons when they are separate and when they are bound together

**Boyles’ Law** the law that states that volume is inversely related to pressure if temperature is held constant

**buoyant force** the upward force exerted by a fluid on an object placed in it

**capacitor** an electrical device used to store charge

**center of mass** the point at which all the mass of an object can be considered to be located

**centripetal acceleration** the rate of change in velocity of a mass moving uniformly in a circle at constant speed; directed radially inward toward the center of the circular path

**centripetal force** the force directed inward along the radius of an object’s circular path

**Charles’ Law** the law that states that volume is directly proportional to temperature if pressure is held constant

**circuit** a closed path of conducting materials through which electricity can flow

**coefficient of friction** the ratio of the friction force between two surfaces and the normal force between those surfaces

**concave lens** a converging lens; a transparent piece of glass or plastic that is thicker in the middle than at the ends.

**concave mirror** a converging mirror; a reflective surface that curves away from an object

**conduction** the transfer of heat between materials that are in contact with one another

**constructive interference** the phenomenon that occurs when two waves combine in such a way that the amplitude of the resulting wave is greater than either of the two individual waves

**convection** the transfer of heat by the movement of a heated substance, such as by currents in a fluid

**convex lens** a diverging lens; a transparent piece of glass or plastic that is thicker at the ends than in the middle

**convex mirror** a diverging mirror; a reflective surface that bulges toward the object

**Coulomb’s Law** the law that states that the magnitude of the force between charged particles is proportional to the product of the two charges and varies inversely as the square of the distance between them

**critical angle** the angle of incidence at which the angle of refraction is 90° relative to the normal

**cross product** the combining of vectors in such a way that the result is a vector

**current** the amount of charge moving through a conductor per second

**density** the mass of a substance divided by its volume

**destructive interference** the phenomenon that occurs when two waves combine in such a way that the amplitude of the resulting wave is less than either of the two individual waves

**diffraction** the bending of waves around an obstacle or through an opening

**direct relationship** a correlation in which two variables increase or decrease simultaneously

**displacement** a change in position of an object, which is a vector quantity

**distance** the length between two points, which is a scalar quantity

**domain** a large groups of atoms with net spins that align

**Doppler effect** a relative change in frequency due to motion of a sound of source or its observer

**dot product** the combining of vectors in such a way that the result is a scalar

**elastic potential energy** the stored potential energy resulting when an object is deformed or distorted, such as a compressed spring

**electric field intensity** the magnitude of the electric field

**electric field** the force exerted on a charged particle by a charged object in the region around the object

**electric potential** the amount of work per unit charge required to move a charge from infinity to another point in an electric field

**electromagnet** a solenoid with an iron core, which forms a magnet that can be controlled

**electromagnetic induction** the process through which an electric current can be induced by a changing magnetic field

**electromagnetic spectrum** the arrangement of electromagnetic waves in order of wavelength

**electromagnetic wave** a traveling disturbance produced by vibrating charges; travels as a series of vibrating electric and magnetic fields at right angles to one another

**electromagnetism** the relationship between electricity and magnetism

**electroscope** an instrument used to determine the presence of small electric charges

**energy** the ability to do work or cause change to a system

**entropy** a measure of the disorder of a system

**force** a push or a pull

**free-body diagram** a picture used to compare the direction and magnitude of the forces exerted on an object

**frequency** the number of revolutions or waves per unit time

**friction** the resistive force that opposes the motion of an object as a result of the contact between two surfaces

**gamma decay** the spontaneous emission of high-energy photons by certain radioactive substances

**generator** a device that transforms mechanical energy into electrical energy

**gravitational constant** the constant *G*, which has a value of 6.67 × 10^{–11} N · m^{2}/kg^{2}, and is used in the equation to calculate the gravitational force

**gravitational force** the force of attraction between any pair of objects as a result of their masses

**gravitational potential energy** the energy an object has because of its position in a gravitational field

**half-life** the time it takes for half of the radioactive nuclei in a sample to decay

**heat energy** the transfer of thermal energy from a warmer substance to a cooler substance

**heat engine** a device that converts heat to mechanical energy by doing work

**heat of fusion** the amount of energy required to change a unit mass of a substance from a solid to a liquid at the melting point

**heat of vaporization** the amount of energy required to change a unit mass of a substance from a liquid to a gas at the boiling point

**impulse** the product of the average force exerted on a mass and the time interval over which the force is exerted; vector quantity

**index of refraction:** the ratio of the speed of light in a vacuum with the speed of light in a specific medium

**indirect relationship** a correlation in which the dependent variable changes opposite to the independent variable

**instantaneous velocity** the velocity of an object at a particular instant

**internal energy** the total amount of energy of the particles and includes potential energy in addition to kinetic energy

**isotopes** atoms of the same element with different numbers of neutrons

**joule** the unit of energy equal to one newton-meter

**Joule’s Law of Heating** the law that states that the heat produced is directly proportional to the square of the current, the resistance, and the time

**kinetic energy** the energy an object has as a result of its motion

**kinetic friction** the resistive force that opposes the movement of an object already in motion

**kinetic theory** the description of matter as being made up of small particles that are in constant motion

**law of charges** the law that states that unlike charges attract one another and like charges repel one another

**law of conservation of energy** the law that states that the total energy of a system remains constant; no new energy is created and no energy is destroyed

**length contraction** the phenomenon in which an observer at rest relative to a moving object traveling at relativistic speeds would observe the length of the object to be shorter than it would be at rest relative to the observer

**longitudinal wave** a wave in which the particles of the medium vibrate parallel to the direction of motion of the wave

**mass defect** the difference between the mass of the unbound nucleons and the mass of the bound nucleons

**mechanical energy** the total of the potential and kinetic energy of a system

**mechanical wave** a traveling disturbance that requires a medium through which to travel

**momentum** the product of the mass and velocity of a moving object; vector quantity

**motor** a device that transforms electrical energy into mechanical energy

**natural frequency** the frequency at which a system that has been disturbed will vibrate once there are no disturbing forces

**normal force** the reaction force exerted on an object by a surface in contact with the object

**nuclear decay** the process through which unstable nuclei release particles or energy in order to gain stability

**nuclear fission** a nuclear reaction in which one large nucleus splits to form smaller nuclei

**nuclear fusion** a nuclear reaction in which two smaller nuclei combine to form a larger one

**Ohm’s Law** the law that states that resistance is directly proportional to voltage and indirectly proportional to current.

**parallel circuit** a circuit through which current can follow multiple paths

**Pascal’s Principle** the rule stating that any external pressure applied to a confined static fluid is distributed uniformly throughout the fluid

**photoelectric effect** the phenomenon in which electrons along the surface of a metal are emitted when electromagnetic energy with a certain minimum frequency is incident on the metal

**photon** a discrete bundle, or quantum, of electromagnetic energy

**pitch** the characteristic of sound that describes how high or low it is perceived; determined by the frequency of the sound wave

**potential energy** the energy an object has as a result of its position or condition

**power** the rate at which work is done or energy is used

**pressure** the force per unit area

**radiation** the transfer of heat by electromagnetic waves, or particles given off by radioactive substances

**radioactivity** the spontaneous emission of radiation

**real image** an image formed by a mirror or lens that exists where rays meet, and which therefore can be focused on a screen

**reflection** the process through which light bounces off a surface

**refraction** the bending of a light ray when it passes at an angle from one medium to another

**resistance** the opposition to the flow of charges offered by a material

**resonance:** the tendency of a system to vibrate at a greater amplitude at some frequencies than others

**resonant frequency** a natural vibrating frequency of an object

**right-hand rule** a method of finding the direction of a magnetic field around a current-carrying wire or the force acting on a wire or charge in magnetic field

**scalar quantity** a quantity that is described by magnitude without regard to direction; examples include mass and temperature

**scientific notation** a shorthand notation for writing very large or small numbers using a coefficient that is greater or equal to 1 and less than 10 multiplied by base 10 to an exponent

**series circuit** a circuit through which current can flow through each element without branching

**significant figures** digits in a number that are known with some degree of certainty

**Snell’s Law of Refraction** the law that states that the ratio of the sine of the angle of incidence to the sine of the angle of refraction is equal to the relative index of refraction for the two mediums

**solenoid** a series of closely spaced coils of wire

**special theory of relativity** the theory proposed by Einstein that suggests that the speed of light is constant in all reference frames, despite any relative motion between an observer and the light source, and the laws of physics are the same in all inertial reference frames

**specific heat** the amount of heat required to raise the temperature of one mass unit by one degree Celsius

**standing wave** a stationary wave pattern formed when two sets of waves with equal wavelength and amplitude interfere

**static friction** the resistive force that opposes the start of motion between two surfaces in contact

**strong force** a short-range force that holds the nucleons of an atom together despite the like charges of the protons

**temperature** the average kinetic energy of the molecules in a sample of matter

**thermal energy** the total kinetic energy of all the particles in a sample of matter

**threshold frequency** the minimum frequency of the incident electromagnetic energy on a metal for the photoelectric effect to be observed

**time dilation** the phenomenon in which an observer at rest relative to a moving object traveling at relativistic speeds would observe the length of time to be longer than it would be at rest relative to the observer

**torque** the tendency of a force to cause rotation about an axis, which is measured as the product of the force and the length of the lever arm

**total internal reflection** the process in which light incident on the boundary between two mediums, passing from the medium with the higher index of refraction, is reflected back into the original medium

**transverse wave** a wave in which the particles of the medium vibrate perpendicular to the direction of motion of the wave

**unbalanced forces** a combination of forces on an object that do not result in a net force of zero

**uniform circular motion** motion around a circle at a constant speed

**uniformly accelerated motion** motion in which an object accelerates at a constant rate

**vector quantity** a quantity that is described by both magnitude and direction; examples include force and acceleration

**virtual image** an image formed by a mirror or lens that exists where rays appear to meet, but do not, and therefore cannot be focused on a screen

**voltage** potential difference, or the amount of electric potential

**voltmeter** a device used to measure voltage

**wave** a disturbance that carries energy from one location to another

**wavelength** the distance between similar points on consecutive waves

**weight** the product of mass and the acceleration due to gravity at a particular location

**work** the product of the force exerted on an object and the distance the object moves as a result of that force

**work-energy theorem** the idea that the work done on a system or by a system equals the change in the energy of the system