Click here to explore thousands of examiner marked IA, EE and TOK exemplars!
Are you studying for your IB exams and need to learn key definitions? This post outlines the top 100 IB Physics definitions so that you will be well-prepared to tackle the exam!
IB Physics Definitions
Core Definitions (SL & HL)
Space, Time, and Motion
Displacement: The instantaneous distance of a moving object from a fixed reference point in a specified direction.
Velocity: The rate of change of displacement with respect to time, which is a vector quantity.
Speed: The rate of change of distance with respect to time, which is a scalar quantity.
Acceleration: The rate of change of velocity with respect to time, representing both changes in speed and changes in direction.
Terminal Speed: The constant maximum speed reached by a falling object when the resistive force of air resistance completely balances the downward force of gravity.
Newton's First Law of Motion: An object will remain at rest or continue to move at a constant velocity unless acted upon by a net external force.
Newton's Second Law of Motion: The net external force acting on an object is directly proportional to the rate of change of its linear momentum.
Newton's Third Law of Motion: When two bodies interact, the force exerted by the first body on the second is equal in magnitude and opposite in direction to the force exerted by the second body on the first.
Law of Conservation of Linear Momentum: The total linear momentum of an isolated system remains constant, provided no external forces act on the system.
Impulse: The product of the net external force acting on an object and the time interval over which it acts, which equals the change in momentum.
Work Done: The product of the magnitude of a force applied to an object and the displacement of the object in the direction of that force.
Principle of Conservation of Energy: Energy cannot be created or destroyed, but can only be transformed from one form to another within an isolated system.
Efficiency: The ratio of useful work or energy output from a system to the total work or energy input into the system.
Thermal Physics
Temperature: A macroscopic measure of the average random kinetic energy of the molecules within a substance.
Internal Energy: The total potential energy and random kinetic energy of the molecules that make up a substance.
Specific Heat Capacity (c): The amount of thermal energy required to raise the temperature of one kilogram of a substance by one Kelvin (or one degree Celsius).
Specific Latent Heat (L): The amount of thermal energy required to change the phase of one kilogram of a substance at a constant temperature.
Ideal Gas: A theoretical gas composed of identical, perfectly elastic point particles that interact only through collisions and obey the gas laws under all conditions.
Conduction: The transfer of thermal energy through a material via atomic vibrations and the movement of free delocalized electrons without bulk movement of the medium.
Convection: The transfer of thermal energy through a fluid (liquid or gas) via the bulk motion of the fluid caused by differences in density.
Radiation: The transfer of energy across space by means of electromagnetic waves without requiring a physical medium.
Wave Behaviour
Simple Harmonic Motion (SHM): A periodic motion where the acceleration of a system is directly proportional to its displacement from a fixed equilibrium position and is always directed toward that equilibrium position.
Transverse Wave: A wave in which the oscillations of the medium particles are perpendicular to the direction of wave propagation and energy transfer.
Longitudinal Wave: A wave in which the oscillations of the medium particles are parallel to the direction of wave propagation and energy transfer.
Wavefront: A line or surface connecting adjacent points of a wave that are currently oscillating in the same phase.
Ray: A line drawn perpendicular to a wavefront that indicates the direction of energy propagation of the wave.
Intensity: The amount of wave energy passing per unit time through a unit area perpendicular to the direction of wave propagation.
Refractive Index (n): The ratio of the speed of electromagnetic waves in a vacuum to the speed of the waves within a given material.
Superposition Principle: When two or more waves of the same type meet at a point, the resultant displacement is the vector sum of the individual displacements of the waves.
Coherent Sources: Two or more wave sources that produce waves with a constant phase relationship and identical frequencies.
Polarized Light: Light waves in which the electric field vectors oscillate within a single geometric plane perpendicular to the direction of propagation.
Fields
Electric Current: The rate of flow of electric charge past a specific point or cross-section in a circuit.
Potential Difference (V): The electrical work done per unit charge when a charge moves from one point to another within an electric field.
Electromotive Force (emf): The total energy per unit charge converted from other forms (such as chemical energy) into electrical energy by a power source.
Ohm's Law: The current flowing through a conductor is directly proportional to the potential difference across it, provided its temperature remains constant.
Internal Resistance: The inherent electrical resistance to the flow of current present inside a power supply or battery itself.
Electric Field Strength (E): The electrostatic force exerted per unit positive test charge placed at a specific point in space.
Magnetic Field Strength / Magnetic Flux Density (B): The magnetic force exerted per unit length on a straight conductor carrying a unit current perpendicular to the field lines.
Gravitational Field Strength (g): The gravitational force exerted per unit mass on a small test mass placed at a specific point in space.
Nuclear and Quantum Physics
Nucleon: A collective term used to describe either a proton or a neutron present within an atomic nucleus.
Isotope: Nuclides that share the same atomic number (number of protons) but possess a different mass number (number of neutrons).
Radioactive Half-Life: The time required for half of the unstable nuclei in a radioactive sample to undergo decay.
Unified Atomic Mass Unit (u): A standard unit of mass defined as exactly one-twelfth of the mass of a single carbon-12 atom at rest.
Mass Defect: The difference between the total combined mass of the individual constituent nucleons and the actual mass of the intact nucleus they form.
Nuclear Binding Energy: The minimum energy required to completely separate an atomic nucleus into its individual constituent nucleons.
Elementary Particle: A fundamental subatomic particle that possesses no known internal structure and cannot be broken down into smaller components.
Antiparticle: A subatomic particle that possesses the exact same mass as its corresponding matter particle but carries an opposite electric charge.
Greenhouse Effect and Energy Production
Albedo: The ratio of the total reflected power of electromagnetic radiation from a surface to the total incident power striking it.
Emissivity: The ratio of the power radiated per unit area by a specific object to the power radiated per unit area by a perfect black body at the same temperature.
Solar Constant: The mean intensity of solar electromagnetic radiation received per unit area at the outer edge of Earth’s atmosphere when Earth is at its average distance from the Sun.
Specific Energy: The total amount of useful energy stored per unit mass of a fuel source, measured in J kg-1.
Energy Density: The total amount of useful energy stored per unit volume of a fuel source, measured in J m-3.
Black Body: A theoretical, idealized physical object that absorbs 100% of all incident electromagnetic radiation falling upon it and is a perfect emitter of thermal radiation.
Astrophysics
Event Horizon: The boundary surrounding a black hole where the escape velocity of the gravitational field matches or exceeds the speed of light in a vacuum.
Schwarschild Radius (Rs): The radius from the centre of a mass configuration inside which the mass must be compressed to form a black hole.
Doppler Redshift (z): The fractional shift toward longer, redder wavelengths observed in electromagnetic radiation when an astronomical light source is moving away from the observer.
HL-Only Definitions
Advanced Motion and Rigid Bodies
Angular Displacement: The angle in radians through which a point or a line has been rotated around a specified axis of rotation.
Angular Velocity (ω): The rate of change of angular displacement with respect to time for a rotating system.
Centripetal Acceleration: The inward radial acceleration experienced by an object undergoing uniform circular motion, directed toward the centre of the circular path.
Torque: The turning or rotational effect produced by a force, calculated as the product of the force and the perpendicular distance from the pivot to the line of action of the force.
Moment of Inertia (I): A measure of a rigid body's rotational inertia, representing its resistance to changes in its angular velocity around a specified axis.
Angular Momentum (L): The rotational analogue of linear momentum, calculated as the product of a body's moment of inertia and its angular velocity.
Advanced Thermodynamics
First Law of Thermodynamics: A statement of conservation of energy applied to thermal systems, where the heat added to a system equals the change in internal energy plus the work done by the system.
Second Law of Thermodynamics: A fundamental law stating that the total entropy of an isolated system can never decrease over time, and thermal energy cannot spontaneously transfer from a cold body to a hot body.
Isothermal Process: A thermodynamic process that occurs at a constant, uniform temperature throughout the change.
Adiabatic Process: A thermodynamic process in which no heat energy is exchanged between the system and its surrounding environment (ΔQ = 0).
Carnot Cycle: An idealized, reversible thermodynamic cycle that represents the maximum theoretical efficiency possible for a heat engine operating between two temperatures.
Wave Phenomena
Resolution (Rayleigh Criterion): Two sources are just resolvable when the principal central maximum of the diffraction pattern of one image coincides with the first minimum of the diffraction pattern of the second image.
Doppler Effect: The observed change in the frequency or wavelength of a wave resulting from the relative motion between the wave source and the observer.
Standing Wave: A wave pattern formed by the superposition of two identical travelling waves moving in opposite directions, characterized by fixed nodes and antinodes.
Node: A point along a standing wave where the amplitude of oscillation is permanently zero due to destructive interference.
Antinode: A point along a standing wave where the amplitude of oscillation reaches its maximum value due to constructive interference.
Brewster's Law: A law stating that when unpolarized light strikes a boundary at a specific polarizing angle, the reflected light is completely plane-polarized parallel to the surface.
Thin-Film Interference: The phenomenon where light waves reflected from the upper and lower boundaries of a thin layer interfere with each other, creating colourful patterns.
Advanced Fields and Potential
Gravitational Potential (Vg): The work done per unit mass in bringing a small test mass from infinity to a specific point within a gravitational field.
Electric Potential (Ve): The work done per unit charge in bringing a small positive test charge from infinity to a specific point within an electric field.
Escape Speed: The minimum speed required for a projectile to escape the gravitational field of a massive body from a given starting position without further propulsion.
Equipotential Surface: A continuous surface or line in space connecting points that all share the exact same gravitational or electrical potential.
Gravitational Potential Energy: The total work done in moving a mass from infinity to a specific position within a gravitational field.
Electromagnetic Induction
Magnetic Flux (ϕ): The product of the magnetic field strength and the cross-sectional area perpendicular to the magnetic field lines through which it passes.
Magnetic Flux Linkage (Nϕ): The product of the magnetic flux passing through a single loop of a coil and the total number of turns in that coil.
Faraday's Law of Electromagnetic Induction: The magnitude of the induced electromotive force (emf) in a circuit is directly proportional to the rate of change of magnetic flux linkage.
Lens's Law: The direction of an induced electromotive force (emf) or current is always such that it creates a magnetic field that opposes the change in magnetic flux that caused it.
Root Mean Square (rms) Current: The value of alternating current that would produce the same average power dissipation in a purely resistive load as an equivalent direct current.
Capacitance (C): The ratio of the charge stored on one of the plates of a capacitor to the potential difference across the plates.
Capacitive Reactance (XC): The opposition offered to the flow of alternating current by a capacitor, which varies inversely with the frequency of the AC signal.
Quantum and Nuclear Physics
Photoelectric Effect: The emission of electrons from the surface of a metal when electromagnetic radiation of sufficiently high frequency strikes the metal surface.
Work Function (ϕ): The minimum energy required to liberate an electron from the surface of a specific metal.
Threshold Frequency (f0): The minimum frequency of incident light required to cause the photoelectric emission of electrons from a metal surface.
De Broglie Wavelength: The wavelength associated with a moving matter particle, showing that matter possesses dual wave-particle characteristics.
Heisenberg’s Uncertainty Principle (Position-Momentum): It is fundamentally impossible to simultaneously measure both the position and momentum of a particle with absolute precision.
Heisenberg’s Uncertainty Principle (Energy-Time): The uncertainty in the energy state of a quantum system is inversely related to the time interval over which that energy state is observed.
Quantum Tunnelling: A quantum mechanical phenomenon where a particle transitions through a potential energy barrier that it cannot classically overcome.
Bohr Model Condition: An electron can only orbit a nucleus stably without radiating energy in discrete, non-radiating orbits where its angular momentum is quantized.
Decay Constant (λ): The probability of decay per unit time for an individual unstable nucleus within a radioactive sample.
Relativistic Mechanics
Lorentz Factor (γ): A dimensionless scaling factor used in special relativity that dictates the magnitude of time dilation and length contraction as speed approaches the speed of light.
Time Dilation: The relativistic phenomenon where the time interval between two events appears longer to an observer moving relative to the frame where the events occurred.
Length Contraction: The relativistic phenomenon where the length of an object is measured to be shorter when it is moving at high speed relative to the observer.
Proper Time (Δt0): The time interval between two events measured by an observer in whose reference frame the two events occur at the exact same spatial position.
Proper Length (L0): The length of an object measured in the rest frame of the object by an observer who is stationary relative to it.
We hope you found this post helpful. For more useful materials associated with the IB, check out the wide variety of IA, EE and TOK exemplars available at Clastify and other guides available on our blog.
The Fast Track To Your
Best IB Coursework & College Essays
All content on this website has been developed independently from and is not endorsed by the International Baccalaureate Organization. International Baccalaureate and IB are registered trademarks owned by the International Baccalaureate Organization.