AEPA Physics (NT308) key terms

A vector quantity giving the straight-line change in position from a starting point to an ending point, including both distance and direction. It differs from distance traveled, which is a scalar and depends on the actual path.

The rate at which displacement changes with time, a vector with both speed and direction. Average velocity is displacement divided by elapsed time; instantaneous velocity is the limit of that ratio as time approaches zero.

The rate at which velocity changes with time, a vector quantity. An object accelerates when it speeds up, slows down, or changes direction, and the acceleration points in the direction of the net force.

The net force on an object equals its mass times its acceleration (F = ma). It links force, mass, and acceleration, and implies that heavier objects need more force for the same acceleration.

The tendency of an object to resist changes in its state of motion. Mass is the quantitative measure of inertia, so a more massive object requires a larger net force to produce a given acceleration.

The product of an object's mass and velocity, a vector quantity. In an isolated system the total momentum stays constant, which is the basis for analyzing collisions and recoil.

In a system with no net external force, the total momentum before an interaction equals the total momentum after it. This principle applies to collisions, explosions, and rocket propulsion.

The product of a force and the time interval over which it acts, equal to the change in an object's momentum. Extending the contact time reduces the peak force for a given momentum change.

The energy transferred to or from an object when a force acts through a displacement, calculated as force times displacement times the cosine of the angle between them. Work is measured in joules.

The energy an object possesses because of its motion, equal to one-half its mass times the square of its speed. Doubling the speed quadruples the kinetic energy.

Energy cannot be created or destroyed, only transferred between forms or between objects. In a closed system the total mechanical energy stays constant when only conservative forces act.

The net force directed toward the center of a circular path that keeps an object moving in that circle. It equals mass times speed squared divided by the radius of the path.

The force exerted perpendicular to a surface divided by the area of that surface. In fluids, pressure increases with depth and is transmitted equally in all directions in a confined fluid.

The upward force a fluid exerts on an object placed in it, equal to the weight of the fluid displaced by the object. An object floats when this force balances its weight.

The mass of a substance per unit volume, commonly expressed in kilograms per cubic meter or grams per cubic centimeter. Density determines whether an object sinks or floats in a given fluid.

A fundamental property of matter that comes in positive and negative types, measured in coulombs. Like charges repel and opposite charges attract, and charge is conserved in isolated systems.

The electrostatic force between two point charges is proportional to the product of the charges and inversely proportional to the square of the distance between them. The force acts along the line joining the charges.

A vector field describing the force per unit positive charge at each point in space around a charge distribution. Field lines point away from positive charge and toward negative charge.

The work required per unit charge to move a charge between two points, measured in volts. It is also called voltage and drives current through a circuit.

The rate at which electric charge flows through a conductor, measured in amperes. One ampere equals one coulomb of charge passing a point per second.

A measure of how strongly a material opposes the flow of electric current, measured in ohms. Resistance depends on material, length, cross-sectional area, and temperature.

For many conductors at constant temperature, current equals voltage divided by resistance (I = V/R). It relates potential difference, current, and resistance in a simple circuit.

A vector field that exerts forces on moving charges and magnetic materials, produced by currents and permanent magnets. Its direction is given by the direction a compass needle points.

The production of an electric potential difference in a conductor by a changing magnetic flux through it. This principle underlies generators, transformers, and many sensors.

The distance between two consecutive corresponding points on a wave, such as crest to crest, measured in meters. Wavelength relates to frequency and wave speed by the wave equation.

The number of complete wave cycles that pass a given point each second, measured in hertz. Frequency is the reciprocal of period and determines pitch for sound and color for light.

The rate at which a wave disturbance travels through a medium, equal to frequency times wavelength. It depends on the properties of the medium rather than on the wave's amplitude.

A condition in which a system is driven at one of its natural frequencies, producing a large-amplitude response. It explains standing waves in instruments and the collapse of structures in wind.

A wave pattern formed by two identical waves traveling in opposite directions, producing fixed nodes and antinodes. Standing waves occur on strings and in air columns at specific resonant frequencies.

The bending of a wave as it passes from one medium into another where its speed differs. The change in direction is described by Snell's law and depends on the indices of refraction.

The spreading of waves as they pass through an opening or around an obstacle. The effect becomes more pronounced when the obstacle or slit is comparable in size to the wavelength.

The combination of two or more waves that overlap, producing regions of greater amplitude where they reinforce and lesser amplitude where they cancel. It is evidence for the wave nature of light.

The ratio of the speed of light in a vacuum to its speed in a given medium. A larger index means light travels more slowly and bends more when entering that material.

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

A measure of the average kinetic energy of the particles in a substance. It determines the direction of heat flow and is measured in kelvin, degrees Celsius, or degrees Fahrenheit.

The state in which two objects in contact exchange no net heat because they are at the same temperature. Net heat flow stops once this condition is reached.

The change in internal energy of a system equals the heat added to it minus the work it does. It is a statement of energy conservation applied to thermal systems.

The total entropy of an isolated system never decreases; heat flows spontaneously from hot to cold. It sets the direction of natural processes and limits the efficiency of heat engines.

A measure of the disorder or number of microscopic arrangements available to a system. Entropy increases in spontaneous processes in isolated systems, reflecting energy dispersal.

The emission of electrons from a metal surface when light above a threshold frequency strikes it. It demonstrates that light carries energy in discrete packets called photons.

A discrete packet of electromagnetic energy whose energy equals Planck's constant times the wave's frequency. Photons have no rest mass and travel at the speed of light.

The minimum energy needed to remove an electron from the surface of a particular metal. In the photoelectric effect, incident photon energy must exceed this value for electrons to be emitted.

The time required for half of the radioactive nuclei in a sample to decay. Each radioactive isotope has a characteristic half-life that does not depend on sample size or conditions.

The spontaneous transformation of an unstable atomic nucleus into a more stable one, emitting particles or energy. Common modes include alpha decay, beta decay, and gamma emission.

The splitting of a heavy nucleus into lighter nuclei, releasing a large amount of energy. It can proceed as a chain reaction when released neutrons trigger further fissions.

A testable, falsifiable proposed explanation for an observed phenomenon. A good hypothesis makes specific predictions that can be checked by experiment or further observation.

The factor that an experimenter deliberately changes or manipulates in an investigation. Its effect is measured through the dependent variable while other conditions are held constant.

The factor that is measured or observed in an experiment and is expected to respond to changes in the independent variable. It represents the outcome of the investigation.

An investigation in which all variables except the independent variable are held constant, and a control group is compared with an experimental group. This design supports causal conclusions.

The digits in a measured value that carry meaningful information about its precision. Rules for significant figures govern how calculated results are rounded to reflect measurement uncertainty.