Georgia Unified Physics key terms

A vector giving the straight-line change in position from a starting point to an ending point, including direction. It differs from distance traveled, which is a scalar measuring total path length.

The rate at which displacement changes with time, a vector quantity with both magnitude and direction. Average velocity divides total displacement by elapsed time; instantaneous velocity is the limit as the time interval shrinks toward zero.

The rate at which velocity changes with time, a vector quantity. An object accelerates when it speeds up, slows down, or changes direction, so circular motion at constant speed still involves acceleration.

The net force on an object equals its mass times its acceleration, written as the vector equation F_net = ma. It links causes of motion (forces) to the resulting change in motion.

A sketch showing one object in isolation with every external force drawn as an arrow acting at the appropriate point, labeled by type and magnitude. Used to set up net-force equations before solving.

The perpendicular contact force a surface exerts on an object resting against it. Its magnitude adjusts to other forces, so on an incline it equals mg cos(theta) rather than simply the object's weight.

A contact force opposing relative sliding or the tendency to slide between surfaces. Static friction adjusts up to a maximum value mu_s times the normal force; kinetic friction is roughly constant at mu_k times the normal force.

The net inward force required to keep an object moving on a circular path, of magnitude mv^2/r. It is not a new kind of force but a role played by tension, gravity, friction, or another force.

In an isolated system, total energy stays constant while transforming between kinetic, potential, thermal, and other forms. Mechanical energy alone is conserved only when no nonconservative forces such as friction do work.

The energy transferred to or from an object by a force acting through a displacement, computed as F d cos(theta) for a constant force. Work is zero when force is perpendicular to displacement.

The rate at which work is done or energy is transferred, measured in watts, where one watt equals one joule per second. Average power equals work divided by time, or force times velocity for constant force.

The impulse delivered by a net force over a time interval equals the object's change in momentum, written J = F_avg * delta_t = delta_p. Extending collision time with the same impulse reduces the average force.

In a system with no net external force, total momentum before an interaction equals total momentum after. It applies to collisions and explosions, and holds separately along each axis.

A collision in which both total momentum and total kinetic energy are conserved. Billiard-ball-like interactions approximate this; in perfectly inelastic collisions the objects stick together and kinetic energy is lost.

Oscillation in which restoring force is proportional and opposite to displacement from equilibrium, producing sinusoidal motion. Period of a mass-spring system depends on mass and spring constant, not amplitude.

The state in which two or more objects in contact have the same temperature, so no net heat flows between them. It is the condition that defines temperature measurement with a thermometer.

Energy transferred between objects because of a temperature difference, measured in joules. Heat flows spontaneously from hotter to colder objects until thermal equilibrium is reached.

The energy needed to raise the temperature of one kilogram of a substance by one kelvin, measured in J/(kg*K). Used in Q = mc delta_T to calculate heating or cooling energy.

Energy absorbed or released during a phase change at constant temperature, per kilogram of substance. Melting and boiling absorb energy; freezing and condensing release it, without changing temperature.

The change in internal energy of a system equals heat added to the system minus work done by the system. It is conservation of energy applied to thermal processes and sign conventions matter.

A thermodynamic change with no heat exchange with the surroundings, so Q = 0 and internal energy change equals negative work done. Rapid compression or expansion approximates adiabatic behavior.

The equation PV = nRT relating pressure, volume, moles, and absolute temperature for a gas model with negligible particle volume and no intermolecular forces. Temperature must be in kelvin.

The entropy of an isolated system never decreases; heat flows spontaneously from hot to cold. It sets the maximum efficiency of heat engines and forbids a perfect converter of heat to work.

A measure of the number of microscopic arrangements consistent with a system's macroscopic state, often described as disorder. It increases in irreversible processes and stays constant in reversible ones.

The distance between consecutive corresponding points on a wave, such as crest to crest, measured in meters. It relates to frequency and speed by v = f lambda.

The number of complete wave cycles passing a point per second, measured in hertz. Frequency is set by the source and stays constant when a wave crosses into a new medium, while speed and wavelength change.

The time for one complete cycle of a repeating motion or wave, measured in seconds and equal to the reciprocal of frequency. It also describes the time for one full oscillation in harmonic motion.

The bending of a wave as it passes between media with different speeds, caused by a change in wavelength while frequency stays fixed. Snell's law relates angles to the refractive indices.

Complete reflection of light at a boundary when traveling from a denser to a less dense medium beyond the critical angle. It underlies optical fibers and is described by n1 sin(theta_c) = n2.

The spreading of waves around obstacles and through openings, most noticeable when the opening is comparable to the wavelength. It explains interference fringes in double-slit and single-slit patterns.

The superposition of waves producing regions of reinforced amplitude (constructive) or canceled amplitude (destructive). Path differences of whole or half wavelengths determine which occurs.

A large amplitude response that occurs when a periodic driving frequency matches a system's natural frequency. It appears in mechanical oscillators, acoustic cavities, and electrical circuits.

The electric force between two point charges is proportional to the product of the charges and inversely proportional to the square of their separation, acting along the line joining them. It is attractive for opposite charges and repulsive for like charges.

The force per unit positive charge at a point in space, a vector pointing away from positive charge and toward negative charge. Field lines map its direction and relative strength.

Electric potential energy per unit charge at a point, measured in volts. Potential difference between two points drives current through a conductor and equals work per unit charge moved between them.

For a conductor at constant temperature, current is proportional to potential difference, written V = IR. Resistance is in ohms, and the relation fails for non-ohmic devices such as filament lamps.

In series, components share one current path and voltages add; in parallel, components share the same voltage and currents add. Equivalent resistance adds directly in series but reciprocally in parallel.

The amount of magnetic field passing through a given area, computed as B A cos(theta), measured in webers. Changing flux through a loop induces an electromotive force according to Faraday's law.

The production of an electromotive force and current in a conductor by a changing magnetic flux through it. Faraday's law gives magnitude; Lenz's law says the induced current opposes the change.

The ejection of electrons from a metal surface when light of sufficiently high frequency strikes it. It shows light delivers energy in discrete photons, with maximum electron energy depending on frequency, not intensity.

A quantum of electromagnetic radiation with energy given by E = hf, where h is Planck's constant. Photon energy depends on frequency, and intensity reflects the number of photons arriving per second.

The minimum energy needed to remove an electron from a metal surface, typically a few electron-volts. In the photoelectric effect, incident photon energy must exceed it for emission to occur.

The time for half the nuclei in a radioactive sample to decay, a constant characteristic of each isotope. After n half-lives, the fraction remaining is (1/2)^n regardless of starting amount.

The spontaneous transformation of unstable nuclei into more stable ones by emitting alpha, beta, or gamma radiation. Each decay conserves charge and nucleon number while releasing energy.

The relation E = mc^2 stating that mass is a form of energy. It explains binding energy in nuclei and the energy released in nuclear reactions as a small loss of mass.

The digits in a measurement that carry meaningful information about precision, including one estimated digit. Results of calculations are rounded to match the least precise input.

The absolute difference between an experimental value and an accepted value, divided by the accepted value, times one hundred. It expresses accuracy, not precision, of a measurement.

The estimated range within which a measured value is likely to lie, reflecting instrument limits and random variation. It is reported with a value and used to judge whether results agree.

Transforming data so a relationship plots as a straight line, such as graphing period squared versus length for a pendulum. The slope then yields a physical constant with clear units.