Praxis Physics 5265 key terms

The product of a constant net force and the time interval over which it acts; it equals the change in an object's momentum and is measured in newton-seconds.

In an isolated system with no net external force, the total vector momentum of all interacting objects stays constant before and after any collision or explosion.

A collision in which both total momentum and total kinetic energy are conserved, so the objects separate with no loss of kinetic energy to deformation, heat, or sound.

A collision in which total momentum is conserved but kinetic energy is not; in the perfectly inelastic case the objects stick together and share a common final velocity.

The acceleration of an object moving on a circular path, directed toward the center, with magnitude v squared divided by the radius of the path.

Motion along a circular path at constant speed, where velocity direction changes continuously and a net inward force supplies the required centripetal acceleration.

The rotational effect of a force, computed as the cross product of the lever-arm vector and the force; it changes an object's angular momentum and is measured in newton-meters.

A body's resistance to angular acceleration, equal to the sum of each mass element times its squared distance from the rotation axis; it depends on axis location and mass distribution.

The rotational analog of linear momentum, equal to moment of inertia times angular velocity for a rigid body; it is conserved when no net external torque acts.

The net work done on an object by all forces equals its change in kinetic energy, linking force and displacement to the object's speed.

When only conservative forces do work, the sum of kinetic and potential energy in a system remains constant, allowing speeds and heights to be related without tracking forces.

The electrostatic force between two point charges is proportional to the product of the charges and inversely proportional to the square of their separation, directed along the line joining them.

The force per unit positive charge at a point in space, a vector quantity whose magnitude and direction determine the force on any charge placed there.

The electric potential energy per unit charge at a point, a scalar measured in volts; only differences in potential have physical significance for moving charges.

The net electric flux through any closed surface equals the enclosed charge divided by the permittivity of free space; it simplifies fields for symmetric charge distributions.

The ratio of stored charge to potential difference across a device; for a parallel-plate capacitor it equals permittivity times plate area divided by plate separation.

Circuit analysis principles: the junction rule states charge is conserved at any node, and the loop rule states the sum of potential differences around any closed loop is zero.

The energy per unit charge supplied by a source such as a battery or generator to drive current around a circuit; it is a potential difference, not a force.

The dot product of the magnetic field and an area vector, giving the field passing perpendicularly through a surface; it is measured in webers and underlies induction.

A changing magnetic flux through a loop induces an electromotive force equal to the negative rate of change of that flux, with the sign given by Lenz's law.

The line integral of magnetic field around a closed loop equals the permeability of free space times the net current enclosed, useful for highly symmetric current distributions.

Oscillation in which restoring force is proportional and opposite to displacement, producing sinusoidal motion with constant period independent of amplitude for ideal systems.

A large amplitude response that occurs when a driving frequency matches a system's natural frequency, limited in real systems by damping.

A wave pattern formed by two identical waves traveling in opposite directions, with fixed nodes and antinodes; boundary conditions restrict it to discrete frequencies.

The change in observed frequency when a source and observer move relative to each other; approach raises frequency and recession lowers it.

The spreading and bending of waves as they pass an obstacle or opening, becoming pronounced when the aperture size is comparable to the wavelength.

The superposition of waves producing regions of reinforced and canceled amplitude; constructive interference requires path differences of whole wavelengths, destructive requires half-wavelength offsets.

Color effects in thin layers caused by interference between light reflected from the top and bottom surfaces, with a possible half-wavelength phase shift at one boundary.

The relation that the product of refractive index and sine of the angle from the normal is constant across an interface between two transparent media.

The complete reflection of light at a boundary when it travels from a denser to a less dense medium at an angle beyond the critical angle.

The change in internal energy of a system equals heat added to the system minus work done by the system, expressing energy conservation for thermal processes.

A thermodynamic process with no heat exchange with the surroundings; work done comes entirely from internal energy, so the gas cools when it expands.

The maximum possible efficiency of a heat engine operating between two reservoirs, equal to one minus the ratio of cold to hot absolute temperatures.

A state function measuring energy dispersal in a system; for a reversible process its change equals heat transferred divided by absolute temperature, and it never decreases for an isolated system.

A characteristic molecular speed in a gas, equal to the square root of the average squared molecular speed; it rises with temperature and falls with molar mass.

A model explaining gas pressure and temperature from molecular motion and collisions with container walls, relating average translational kinetic energy to absolute temperature.

In thermal equilibrium each quadratic degree of freedom of a molecule carries an average energy of one-half kT, determining the internal energy of a gas.

The emission of electrons from a metal surface struck by light above a threshold frequency, explained by photons transferring discrete energy packets to electrons.

The minimum energy needed to remove an electron from a metal surface; in the photoelectric effect it equals photon energy minus maximum electron kinetic energy.

The energy carried by a single quantum of electromagnetic radiation, equal to Planck's constant times the radiation frequency, or Planck's constant times light speed divided by wavelength.

The wavelength associated with a particle, equal to Planck's constant divided by the particle's momentum; it becomes significant for low-mass particles.

The principle that mass is a form of energy, with rest energy equal to mass times the square of light speed; it explains energy release in nuclear reactions.

The energy required to separate a bound system completely, such as the energy needed to remove a nucleon from a nucleus; the mass defect equals this energy divided by light speed squared.

The spontaneous transformation of unstable nuclei emitting alpha, beta, or gamma radiation; activity decreases exponentially with a characteristic half-life.

The digits in a measured value that carry meaningful information about precision; rules govern rounding results of multiplication, division, addition, and subtraction.

The procedure for combining individual measurement uncertainties to estimate uncertainty in a calculated result, using absolute uncertainties for sums and relative uncertainties for products.

A consistent bias in measurements caused by faulty instruments or flawed procedure; it shifts results in one direction and is not reduced by averaging repeated trials.

Unpredictable scatter in repeated measurements from uncontrolled variables; averaging many trials reduces its effect on the mean but does not eliminate the spread.

A measure of the spread of repeated measurements about their mean, equal to the square root of the average squared deviation; it quantifies random uncertainty.

A statistical method fitting a straight line to data by minimizing squared residuals, yielding a slope and intercept used to extract physical constants from a graph.