OAE Physics (035) key terms

A cyclical process of observing, forming testable hypotheses, designing controlled experiments, analyzing data, and revising explanations based on evidence. Conclusions are provisional and open to replication and peer scrutiny.

A testable, falsifiable proposed explanation for an observed pattern, stated precisely enough that data could support or contradict it. It guides experimental design rather than serving as a settled conclusion.

A factor held constant across experimental trials so that observed changes can be attributed to the manipulated variable. Uncontrolled variables confound results and weaken causal claims.

Pre-publication evaluation of a study's methods and reasoning by independent experts in the field. It filters obvious errors and unsupported claims but does not guarantee correctness.

A broad, well-tested explanatory framework supported by many independent lines of evidence, such as thermodynamics or evolution. In science the word does not mean a guess or speculation.

A concise statement, often mathematical, describing a regular relationship observed in nature, such as Newton's second law. Laws describe patterns; they do not by themselves explain underlying mechanisms.

The digits in a measurement that carry meaningful information about precision, including one estimated digit. Addition and subtraction keep the least precise decimal place; multiplication and division keep the fewest significant figures.

A compact way of writing very large or small numbers as a coefficient between 1 and 10 multiplied by a power of ten. It simplifies unit conversion and keeps track of order of magnitude.

The internationally agreed measurement system built on seven base units, including the meter, kilogram, second, ampere, kelvin, mole, and candela. Derived units such as newtons and joules combine these bases.

Checking or converting units by treating them as algebraic quantities that must match on both sides of an equation. It catches setup errors and predicts the form of a relationship.

The estimated range within which a measured value likely lies, arising from instrument limits and random or systematic error. Reporting it communicates how much confidence a result deserves.

Accuracy is closeness to the true value; precision is closeness of repeated measurements to one another. A miscalibrated instrument can be precise yet inaccurate, so both must be evaluated.

First: objects keep constant velocity unless a net force acts. Second: net force equals mass times acceleration. Third: forces between two bodies are equal and opposite. Together they explain most everyday motion.

An object's resistance to changes in its state of motion, quantified by its mass. Greater mass means a smaller acceleration for the same net force.

A sketch isolating one object and showing every external force acting on it as labeled arrows. It is the standard first step for applying Newton's second law to a problem.

A contact force opposing relative sliding or the tendency to slide between surfaces. Static friction adjusts up to a maximum; kinetic friction stays roughly constant once motion begins.

The perpendicular push a surface exerts on an object resting against it, adjusting to prevent penetration. On a flat surface it equals weight only when no other vertical forces act.

The product of mass and velocity, a vector quantity. In an isolated system total momentum is conserved in every collision, elastic or inelastic.

The product of an average force and the time over which it acts, equal to the change in momentum. Extending collision time with padding or airbags reduces peak force.

Energy can be transferred or transformed but never created or destroyed within an isolated system. Tracking energy between kinetic, potential, and thermal forms solves many mechanics problems without forces.

The energy transferred when a force moves an object along a displacement, calculated as the force component parallel to the displacement times the distance. Force perpendicular to motion does no work.

The rate at which work is done or energy is transferred, measured in watts, equal to one joule per second. It describes how fast energy moves, not how much.

The net inward force that keeps an object moving in a circular path, directed toward the center. It changes direction of velocity, not speed, and equals mass times speed squared over radius.

A measure of rotational motion equal to moment of inertia times angular velocity for a rigid body. It remains constant when no external torque acts, explaining why spinning skaters speed up when pulling in their arms.

The rotational effect of a force, equal to force times lever arm measured perpendicular to the force line. Net torque causes angular acceleration, and zero net torque means rotational equilibrium.

The electric force between two point charges is proportional to the product of the charges and inversely proportional to the square of their separation. 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.

The electric potential energy per unit charge at a point, measured in volts relative to a chosen reference. Charges spontaneously move from higher to lower potential, and potential difference drives current.

For a resistor at constant temperature, current equals voltage divided by resistance. It is an empirical relationship for ohmic materials, not a universal law of nature.

In series, components share one current path, so current is the same and voltages add. In parallel, components share the same voltage and branch currents add, giving lower total resistance.

The rate at which a circuit transfers electrical energy, equal to current times voltage, or current squared times resistance. It determines heating in resistors and energy use in appliances.

A vector field produced by moving charges and magnets that exerts forces on other moving charges and magnetic materials. Its direction is given by the north pole of a compass needle.

The generation of an electromotive force in a conductor by a changing magnetic flux through it. This principle underlies generators, transformers, and wireless charging.

An induced current flows in the direction whose magnetic field opposes the change in flux that produced it. This consequence of energy conservation means induction always resists the change.

The total force on a charge moving through electric and magnetic fields. The magnetic part is perpendicular to both velocity and field, so it curves paths without changing speed.

Waves are characterized by amplitude, wavelength, frequency, period, and speed, related by speed equals frequency times wavelength. Amplitude relates to energy, while frequency sets pitch or color.

Overlapping waves add algebraically, producing constructive reinforcement where crests align and destructive cancellation where crest meets trough. Stable interference patterns require coherent sources.

The spreading and bending of waves around obstacles and through openings, most noticeable when aperture size is comparable to wavelength. It explains why sound bends around corners more than light.

The change in direction of a wave crossing into a medium where its speed differs, described by Snell's law. Light bending toward the normal when entering glass reflects its slower speed there.

The shift in observed frequency when a wave source and observer move relative to each other. Approaching sources are observed at higher frequency and receding sources at lower frequency.

The ordered range of electromagnetic radiation from radio waves through microwaves, infrared, visible light, ultraviolet, X-rays, and gamma rays. All travel at light speed in vacuum but differ in wavelength and photon energy.

Emission of electrons from a metal surface struck by light above a threshold frequency. It demonstrates that light delivers energy in discrete photons rather than continuously.

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

The total entropy of an isolated system never decreases; heat flows spontaneously from hotter to colder bodies. It sets the direction of natural processes and limits heat engine efficiency.

A measure of the number of microscopic arrangements consistent with a system's macroscopic state, often described as disorder. It increases in spontaneous processes and never decreases in isolation.

Heat is energy transferred due to a temperature difference; temperature measures average molecular kinetic energy. Adding heat does not always raise temperature, as during phase changes.

The energy needed to raise one kilogram of a substance by one kelvin, measured in joules per kilogram-kelvin. Water's high value explains its role in climate and cooling systems.

Energy absorbed or released during a phase change at constant temperature, such as melting or boiling. It breaks or forms intermolecular bonds rather than increasing molecular kinetic energy.

A model treating a gas as many tiny particles in random motion whose collisions with walls create pressure. Average kinetic energy is proportional to absolute temperature.

The relationship pressure times volume equals the number of moles times the gas constant times absolute temperature. It combines Boyle's, Charles's, and Avogadro's laws for dilute gases.

Einstein's framework in which the speed of light in vacuum is the same for all inertial observers. It predicts time dilation, length contraction, and mass-energy equivalence at speeds near light speed.

The principle that mass and energy are interchangeable, expressed as energy equals mass times the speed of light squared. It explains energy release in nuclear reactions and particle annihilation.

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

The principle that light and matter exhibit both wave and particle behavior depending on the experiment. Interference reveals waves; the photoelectric effect and single-particle detection reveal particles.

The wavelength associated with a moving particle, equal to Planck's constant divided by its momentum. It becomes measurable for electrons and explains electron diffraction patterns.

Discrete allowed energies that bound electrons in atoms or nuclei can occupy. Transitions between levels emit or absorb photons of specific frequencies, producing line spectra.

Spontaneous transformation of unstable nuclei by alpha, beta, or gamma emission, changing identity or energy state. Each decay type has a characteristic half-life and penetrating power.

The time required for half the nuclei in a radioactive sample to decay, independent of starting quantity. It enables radiometric dating and radiation-safety planning.