AP Physics 1: Algebra-Based Vocabulary

Acceleration

The rate at which an object’s velocity changes over a period of time.

Example: "A car traveling at 20 m/s that reaches 35 m/s in 5 seconds has an          of (35 – 20) / 5 = 3 m/s², directed in the same direction as its motion."

Acceleration vector

Instantaneous acceleration found by taking the derivative of the velocity function with respect to time in unit vector notation.

Example: "If a particle's velocity function is v(t) = (3t²)î + (2t)ĵ m/s, then the          is found by differentiating: a(t) = (6t)î + 2ĵ m/s²."

Accuracy

The degree to which a measured value agrees with an accepted reference value for that measurement.

Example: "A student measures the acceleration due to gravity as 9.78 m/s², which is very close to the accepted value of 9.80 m/s², demonstrating high          even if the measurements were not perfectly precise."

Air resistance

A frictional force that slows the motion of objects as they travel through the air; when solving basic physics problems, air resistance is assumed to be zero.

Example: "When solving projectile motion problems on the AP Physics 1 exam,          is typically assumed to be zero so that only gravity acts on the object, simplifying the equations of motion."

Amplitude

The maximum displacement from the equilibrium position of an object oscillating around the equilibrium position.

Example: "A mass on a spring pulled 0.15 m from its equilibrium position and released oscillates with an          of 0.15 m, meaning it reaches 0.15 m on either side of equilibrium during each cycle."

Amplitude (A)

Maximum displacement from the equilibrium position of an object oscillating around the equilibrium position.

Example: "For a pendulum swinging with amplitude A = 0.10 m, the restoring force is greatest when the bob is at maximum displacement and zero as it passes through equilibrium."

Analytical method

The method of determining the magnitude and direction of a resultant vector using the Pythagorean theorem and trigonometric identities.

Example: "To find the resultant of two displacement vectors—one of 30 m east and one of 40 m north—the          uses the Pythagorean theorem to give a magnitude of √(30² + 40²) = 50 m at an angle of arctan(40/30) = 53° north of east."

Angular frequency

Ω,ω, rate of change of an angle with which an object that is moving on a circular path.

Example: "A wheel rotating at a frequency of 2 Hz has an          of ω = 2πf = 4π rad/s, which describes how rapidly the angle changes with time."

Angular momentum

Rotational analog of linear momentum, found by taking the product of moment of inertia and angular velocity.

Example: "A spinning figure skater with a moment of inertia I = 2.0 kg·m² and angular velocity ω = 3.0 rad/s has an          of L = Iω = 6.0 kg·m²/s, which is conserved when no external torques act."

Angular position

Angle a body has rotated through in a fixed coordinate system.

Example: "As a wheel rotates from its reference mark through π/2 radians, its          changes from 0 to π/2 rad (90°), indicating a quarter-turn in the fixed coordinate system."

Angular velocity

The rate of change of angular position of a rotating object; measured in radians per second (rad/s).

Example: "A turntable that completes one full revolution (2π radians) every 0.5 seconds has an          of ω = 2π / 0.5 = 4π rad/s ≈ 12.6 rad/s."

Antinode

The location of maximum amplitude in standing waves.

Example: "In a standing wave on a guitar string fixed at both ends, the          occur at the points of maximum amplitude halfway between each pair of adjacent nodes."

Antiparallel vectors

Two vectors with directions that differ by 180°180°.

Example: "Gravity (pointing downward at –9.8 m/s² ĵ) and the normal force on an object resting on a horizontal surface (pointing upward at +9.8 m/s² ĵ) are          because they differ in direction by exactly 180°."

Apparent weight

Reading of the weight of an object on a scale that does not account for acceleration.

Example: "A 70 kg person standing in an elevator accelerating upward at 2 m/s² reads an          of F = m(g + a) = 70(9.8 + 2) = 826 N on a scale, rather than their true weight of 686 N."

Arc length

The distance traveled along a circular path; equal to the radius multiplied by the angle in radians.

Example: "A point on the rim of a wheel of radius 0.5 m that rotates through an angle of 2 radians travels an          of s = rθ = (0.5)(2) = 1.0 m along the circular path."

Area vector

Vector with magnitude equal to the area of a surface and direction perpendicular to the surface.

Example: "For a flat loop of wire with area 0.04 m² lying in the xy-plane, the          has magnitude 0.04 m² and points in the z-direction, perpendicular to the surface of the loop."

Average acceleration

The change in velocity divided by the time over which it changes.

Example: "A sprinter who goes from rest to 8 m/s in 4 seconds has an          of Δv/Δt = (8 – 0) / 4 = 2 m/s² in the direction of motion."

Average power

Work done in a time interval divided by the time interval.

Example: "A motor that does 600 J of work lifting a crate over a period of 10 seconds delivers an          of P = W/t = 600/10 = 60 W."

Average speed

Distance traveled divided by time during which motion occurs.

Example: "A runner who covers a 400 m track in 50 seconds has an          of 400/50 = 8 m/s, regardless of any direction changes made along the way."

Average velocity

The displacement divided by the time over which displacement occurs under constant acceleration.

Example: "An object undergoing constant acceleration that starts at position x = 2 m and ends at x = 20 m over 6 seconds has an          of Δx/Δt = 18/6 = 3 m/s in the positive direction."

Banked curve

The curve in a road that is sloping in a manner that helps a vehicle negotiate the curve.

Example: "A highway curve banked at an angle θ allows a car of any mass to navigate the turn without friction at the design speed, because the horizontal component of the normal force provides the centripetal force: N sinθ = mv²/r."

Base quantity

Physical quantity chosen by convention and practical considerations such that all other physical quantities can be expressed as algebraic combinations of them.

Example: "Length, mass, and time are base quantities in the SI system because all kinematic and dynamic quantities—such as velocity (m/s) and force (kg·m/s²)—can be expressed as algebraic combinations of them."

Base unit

Standard for expressing the measurement of a base quantity within a particular system of units; defined by a particular procedure used to measure the corresponding base quantity.

Example: "The kilogram is the          for mass in the SI system, and it provides the standard against which all mass measurements are compared."

Beat frequency

Frequency of beats produced by sound waves that differ in frequency.

Example: "Two tuning forks vibrating at 440 Hz and 444 Hz produce a          of |444 – 440| = 4 Hz, meaning the sound alternates between loud and soft four times per second."

Beats

Constructive and destructive interference of two or more frequencies of sound.

Example: "When two sound waves of nearly equal frequencies overlap, their constructive and destructive interference produces         —periodic variations in loudness that a musician can use to tune an instrument."

Boundary

Imagined walls that separate the system and its surroundings.

Example: "In a thermodynamics problem, the          of the system is the imaginary surface separating the gas inside a piston from the external environment, across which energy may be transferred as heat or work."

Bow wake

V-shaped disturbance created when the wave source moves faster than the wave propagation speed.

Example: "A speedboat creates a V-shaped          on the water's surface because it is moving faster than the speed of the water waves it generates, causing the wave fronts to pile up into a characteristic wedge pattern."

Bulk strain

(or volume strain) strain under the bulk stress, given as fractional change in volume.

Example: "A steel sphere subjected to uniform pressure from all sides experiences          equal to the fractional change in its volume ΔV/V₀, which is very small due to steel's high bulk modulus."

Bulk stress

(or volume stress) stress caused by compressive forces, in all directions.

Example: "A submarine hull exposed to the pressure of deep ocean water experiences          because the compressive force acts uniformly from all directions, tending to reduce the hull's volume."

Calorie (cal)

Energy needed to change the temperature of 1.00 g of water by 1.00°C1.00°C.

Example: "Heating 50.0 g of water from 20.0°C to 30.0°C requires 50.0 × 10.0 = 500 cal of energy, since by definition one calorie raises 1.00 g of water by 1.00°C."

Calorimetry

Study of heat transfer inside a container impervious to heat.

Example: "In a          experiment, a hot metal block is dropped into a thermally insulated container of water, and the final equilibrium temperature is used to calculate the specific heat of the metal via Qlost = Qgained."

Capacitor

Device that stores electrical charge and electrical energy.

Example: "A parallel-plate          with capacitance C = 50 μF connected to a 12 V battery stores charge Q = CV = (50 × 10⁻⁶)(12) = 6.0 × 10⁻⁴ C and electrical energy U = ½CV² = 3.6 × 10⁻³ J."

Carrier particle

A fundamental particle of nature that is surrounded by a characteristic force field; photons are carrier particles of the electromagnetic force.

Example: "The electromagnetic force between two charged particles is mediated by the exchange of photons, which are the          of that fundamental interaction."

Celsius scale

Temperature scale in which the freezing point of water is 0°C0°C and the boiling point of water is 100°C100°C.

Example: "To convert a temperature of 25°C to the absolute Kelvin scale for use in the ideal gas law PV = nRT, one adds 273.15 to obtain T = 298.15 K, since the          is offset from the Kelvin scale by 273.15 degrees."

Center of gravity

The point where the total weight of the body is assumed to be concentrated.

Example: "For a uniform meter stick, the          is located at the 50 cm mark, and the stick will balance perfectly on a fulcrum placed at that point because the gravitational torques on both sides are equal."

Center of mass

The point where the entire mass of an object can be thought to be concentrated.

Example: "For two objects of mass 2 kg at x = 0 m and 4 kg at x = 3 m, the          is located at x_cm = (2·0 + 4·3)/(2 + 4) = 2 m from the first object."

Centrifugal force

A fictitious force that tends to throw an object off when the object is rotating in a non-inertial frame of reference.

Example: "A passenger in a car turning left feels pushed to the right by what seems like a         , but this is a fictitious force arising from the car's non-inertial (rotating) reference frame—in an inertial frame, the passenger is simply continuing in a straight line."

Centripetal acceleration

Component of acceleration of an object moving in a circle that is directed radially inward toward the center of the circle.

Example: "A 0.5 kg ball moving in a circle of radius 2 m at a constant speed of 4 m/s has a          of a_c = v²/r = 16/2 = 8 m/s² directed toward the center of the circle."

Change in angular velocity

The difference between final and initial values of angular velocity.

Example: "A spinning top that slows from ωi = 10 rad/s to ωf = 4 rad/s experiences a          of Δω = ωf – ωi = –6 rad/s, indicating a decrease in rotational speed."

Change in momentum

The difference between the final and initial momentum; the mass times the change in velocity.

Example: "A 0.5 kg ball initially moving at 6 m/s to the right that rebounds at 6 m/s to the left undergoes a          of Δp = m Δv = 0.5(–6 – 6) = –6 kg·m/s, equal to the impulse applied by the wall."

Charging by induction

Process by which an electrically charged object brought near a neutral object creates a charge separation in that object.

Example: "By bringing a positively charged rod near (but not touching) a neutral metal sphere and then grounding the sphere momentarily,          leaves the sphere with a net negative charge after the ground connection is broken and the rod removed."

Chemical energy

The energy in a substance stored in the bonds between atoms and molecules that can be released in a chemical reaction.

Example: "When gasoline combusts in a car engine, the          stored in the molecular bonds is converted into thermal energy and mechanical work, propelling the vehicle forward."

Circuit

Complete path that an electrical current travels along.

Example: "A simple          consists of a 9 V battery connected by conducting wires to a 3 Ω resistor, allowing a current of I = V/R = 9/3 = 3 A to flow continuously around the closed loop."

Classical relativity

The study of relative velocities in situations where speeds are less than about 1% of the speed of light—that is, less than 3000 km/s.

Example: "A passenger on a train moving at 30 m/s throws a ball forward at 10 m/s; by         , a stationary observer on the platform sees the ball moving at 30 + 10 = 40 m/s, since this speed is far below 3000 km/s."

Closed system

System for which the mass is constant and the net external force on the system is zero.

Example: "Two ice skaters pushing off each other on frictionless ice form a         : their total mass is constant and there is no net external horizontal force, so their combined momentum remains zero throughout the interaction."

Coefficient of linear expansion

(αα) material property that gives the change in length, per unit length, per 1-°C1-°C change in temperature; a constant used in the calculation of linear expansion; the coefficient of linear expansion depends to some degree on the temperature of the material.

Example: "A steel rod (α = 1.2 × 10⁻⁵ °C⁻¹) of length 2.0 m will elongate by ΔL = αL₀ΔT = (1.2 × 10⁻⁵)(2.0)(100) = 2.4 × 10⁻³ m = 2.4 mm when heated from 20°C to 120°C, which structural engineers must account for in bridge design."

Coefficient of performance

Measure of effectiveness of a refrigerator or heat pump.

Example: "A refrigerator with a          of 4.0 removes 4.0 J of heat from the cold reservoir for every 1.0 J of electrical work input, making it an efficient cooling device."

Coefficient of volume expansion

(ββ) similar to αα but gives the change in volume, per unit volume, per 1-°C1-°C change in temperature.

Example: "A liquid with β = 2.1 × 10⁻⁴ /°C occupying 500 mL that is heated by 30°C will expand by ΔV = βV₀ΔT = (2.1 × 10⁻⁴)(500)(30) = 3.15 mL."

Commutative

Refers to the interchangeability of order in a function; vector addition is commutative because the order in which vectors are added together does not affect the final sum.

Example: "Vector addition is         : displacing a particle 5 m east and then 3 m north produces the same final position as displacing it 3 m north first and then 5 m east, because A + B = B + A."

Component (of a 2-d vector)

A piece of a vector that points in either the vertical or the horizontal direction; every 2-d vector can be expressed as a sum of two vertical and horizontal vector components.

Example: "A force vector of 100 N directed at 37° above the horizontal has a horizontal component of Fx = 100 cos(37°) ≈ 80 N and a vertical component of Fy = 100 sin(37°) ≈ 60 N."

Component form of a vector

A vector written as the vector sum of its components in terms of unit vectors.

Example: "A velocity of 5 m/s at 53° above the positive x-axis can be written in component form as v = (5 cos53°)î + (5 sin53°)ĵ = 3î + 4ĵ m/s."

Compressive strain

Strain that occurs when forces are contracting an object, causing its shortening.

Example: "A concrete column 2.0 m tall that shortens by 0.002 m under a heavy load experiences a          of ΔL/L₀ = 0.002/2.0 = 0.001, or 0.1%."

Compressive stress

Stress caused by compressive forces, only in one direction.

Example: "A pillar supporting a building experiences          equal to the applied force divided by its cross-sectional area (σ = F/A), causing the material to shorten along the vertical axis."

Conduction

Heat transfer through stationary matter by physical contact.

Example: "Heat flows from a hot metal pan through          into a wooden handle touching it, transferring thermal energy by direct physical contact between the atoms of the two materials."

Conduction electron

Electron that is free to move away from its atomic orbit.

Example: "In a copper wire,          move freely between atoms when an electric field is applied, creating a conventional current in the opposite direction to electron flow."

Conductor

Material that allows electrons to move separately from their atomic orbits; object with properties that allow charges to move about freely within it.

Example: "Copper is an excellent electrical          because its outer electrons are loosely bound and free to move throughout the metal lattice, enabling charges to redistribute rapidly in response to an electric field."

Conservation of energy

The total mechanical energy (kinetic plus potential) of an isolated system remains constant if only conservative forces act; energy cannot be created or destroyed, only converted between forms.

Example: "A 2 kg ball dropped from rest at a height of 5 m has zero kinetic energy initially; just before hitting the ground, all the gravitational potential energy (mgh = 2 × 9.8 × 5 = 98 J) has converted to kinetic energy, consistent with         ."

Conservation of mechanical energy

The rule that the sum of the kinetic energies and potential energies remains constant if only conservative forces act on and within a system.

Example: "A roller coaster at the top of a 20 m hill has gravitational potential energy mgh that converts entirely to kinetic energy (½mv²) at the bottom, giving v = √(2gh) = √(2 × 9.8 × 20) ≈ 19.8 m/s, assuming no friction."

Conservation of momentum principle

When the net external force is zero, the total momentum of the system is conserved or constant.

Example: "In a head-on collision between a 3 kg cart moving at 4 m/s and a stationary 1 kg cart on a frictionless track, the total momentum before (12 kg·m/s) must equal the total momentum after, since there is no net external force."

Conservative force

A force that does the same work for any given initial and final configuration, regardless of the path followed.

Example: "Gravity is a         : whether a ball falls straight down or slides down a frictionless ramp of any shape, the work done by gravity depends only on the vertical displacement, not on the path taken."

Conserved quantity

One that cannot be created or destroyed, but may be transformed between different forms of itself.

Example: "Total energy is a         —in a pendulum swinging without friction, energy continuously converts between gravitational potential and kinetic forms, but the total always remains constant."

Constructive interference

When two waves arrive at the same point exactly in phase; that is, the crests of the two waves are precisely aligned, as are the troughs.

Example: "When two water waves of amplitude A = 0.5 m arrive at a point in phase (path difference = nλ), they undergo         , producing a resultant wave of amplitude 2A = 1.0 m at that location."

Continuous charge distribution

Total source charge composed of so large a number of elementary charges that it must be treated as continuous, rather than discrete.

Example: "To find the electric field on the axis of a uniformly charged ring, the ring is treated as a          and integrated using dE = k dq / r², because the ring contains so many closely spaced charges that a discrete sum is impractical."

Conventional current

Current that flows through a circuit from the positive terminal of a battery through the circuit to the negative terminal of the battery.

Example: "In a circuit,          flows from the positive terminal of the battery through the external resistors to the negative terminal, even though the actual charge carriers (electrons) move in the opposite direction inside the wire."

Conversion factor

A ratio that expresses how many of one unit are equal to another unit.

Example: "To convert 60 miles per hour to meters per second, you use         : 60 mi/h × (1609 m / 1 mi) × (1 h / 3600 s) ≈ 26.8 m/s."

Coriolis force

The fictitious force causing the apparent deflection of moving objects when viewed in a rotating frame of reference.

Example: "Hurricanes rotate counterclockwise in the Northern Hemisphere because the         —a fictitious force arising from Earth's rotation—deflects moving air masses to the right as seen from a rotating reference frame."

Corkscrew right-hand rule

A rule used to determine the direction of the vector product.

Example: "To find the direction of the torque τ = r × F, you apply the         : curl the fingers of your right hand from r toward F, and your thumb points in the direction of the resulting torque vector."

Cosmic rays

Comprised of particles that originate mainly from outside the solar system and reach Earth.

Example: "High-energy          originating from outside the solar system continuously bombard Earth's upper atmosphere, producing secondary showers of particles that are detected at ground level."

Coulomb interaction

The interaction between two charged particles generated by the Coulomb forces they exert on one another.

Example: "The          between a proton (+e) and an electron (–e) separated by 5.3 × 10⁻¹¹ m in a hydrogen atom provides the centripetal force that keeps the electron in its orbit."

Coulomb's law

The mathematical equation calculating the electrostatic force vector between two charged particles.

Example: "        , F = kq₁q₂/r², shows that if the separation between two charges is doubled, the electrostatic force decreases by a factor of four, illustrating the inverse-square dependence on distance."

Coulomb’s law

Mathematical equation calculating the electrostatic force vector between two charged particles.

Example: "        , F = kq₁q₂/r², shows that if the separation between two charges is doubled, the electrostatic force decreases by a factor of four, illustrating the inverse-square dependence on distance."

Critical damping

The condition in which the damping of an oscillator causes it to return as quickly as possible to its equilibrium position without oscillating back and forth about this position.

Example: "The shock absorbers in a car are designed to produce          so that after hitting a bump, the car returns to its equilibrium height as quickly as possible without bouncing up and down."

Critical point

For a given substance, the combination of temperature and pressure above which the liquid and gas phases are indistinguishable.

Example: "For water, the          occurs at T = 374°C and P = 22.1 MPa; above this temperature and pressure, the liquid and gas phases of water are indistinguishable, forming a single supercritical fluid phase."

Critically damped

Condition in which the damping of an oscillator causes it to return as quickly as possible to its equilibrium position without oscillating back and forth about this position.

Example: "A door closer is          when it shuts in the minimum time without swinging back—the system returns to equilibrium in the shortest possible time without oscillating."

Current density

Flow of charge through a cross-sectional area divided by the area.

Example: "A copper wire of cross-sectional area 2.0 × 10⁻⁶ m² carrying a current of 4.0 A has a          of J = I/A = 4.0/2.0 × 10⁻⁶ = 2.0 × 10⁶ A/m², which is related to the electric field by J = σE."

Cyclic process

Process in which the state of the system at the end is same as the state at the beginning.

Example: "In an ideal Carnot cycle, the gas undergoes isothermal expansion, adiabatic expansion, isothermal compression, and adiabatic compression, returning to exactly its initial pressure, volume, and temperature—a         ."

Cyclotron

Device used to accelerate charged particles to large kinetic energies.

Example: "In a         , protons are accelerated in a spiral path by alternating electric fields within the dees while a perpendicular magnetic field curves their trajectory, increasing their kinetic energy with each pass."

Cylindrical symmetry

System only varies with distance from the axis, not direction.

Example: "A long straight wire carrying current has         —the magnetic field magnitude depends only on the radial distance r from the wire's axis, not on the angular direction around it."

Dalton’s law of partial pressures

Physical law that states that the total pressure of a gas is the sum of partial pressures of the component gases.

Example: "A gas mixture of nitrogen at 40 kPa, oxygen at 21 kPa, and argon at 1 kPa has a total pressure of 62 kPa, as given by         : Ptotal = PN₂ + PO₂ + PAr."

Deceleration

Acceleration in the direction opposite to velocity; acceleration that results in a decrease in velocity.

Example: "A car traveling at 25 m/s that brakes to a stop in 5 seconds has a          (acceleration opposite to velocity) of magnitude a = Δv/Δt = 25/5 = 5 m/s², directed opposite to its motion."

Decibel

A logarithmic unit used to measure sound intensity level; a difference of 10 dB corresponds to a tenfold increase in intensity.

Example: "A sound measured at 70 dB is ten times more intense than a 60 dB sound, because each 10 dB increase represents a tenfold increase in sound intensity according to the logarithmic          scale."

Dees

Large metal containers used in cyclotrons that serve contain a stream of charged particles as their speed is increased.

Example: "Inside a cyclotron, two hollow D-shaped metal containers called          enclose the charged particles as they travel in semicircular arcs, shielding them from the electric field while the magnetic field bends their path."

Defibrillator

A machine used to provide an electrical shock to a heart attack victim's heart in order to restore the heart's normal rhythmic pattern.

Example: "A          rapidly discharges a capacitor through a patient's chest, delivering a brief but powerful electrical pulse—on the order of several hundred joules—that can restore normal sinus rhythm to a fibrillating heart."

Degree of freedom

Independent kind of motion possessing energy, such as the kinetic energy of motion in one of the three orthogonal spatial directions.

Example: "A monatomic ideal gas (like helium) has three translational degrees of freedom—one for each spatial direction—so its average thermal energy per molecule is 3 × (½kBT) = (3/2)kBT."

Derived quantity

Physical quantity defined using algebraic combinations of base quantities.

Example: "Speed is a          because it is defined as distance divided by time (v = d/t), combining the base quantities of length and time rather than being independently defined."

Derived units

Units that can be calculated using algebraic combinations of the fundamental units.

Example: "The newton (N) is a derived unit for force, defined as 1 kg·m/s² by combining the SI base units of mass, length, and time through Newton's second law: F = ma."

Destructive interference

When two identical waves arrive at the same point exactly out of phase; that is, precisely aligned crest to trough.

Example: "In Young's double-slit experiment,          occurs at positions where the path difference is a half-integer multiple of the wavelength (Δr = (m + ½)λ), producing dark fringes on the screen where the two waves cancel."

Dielectric

Insulating material used to fill the space between two plates.

Example: "Inserting a glass          (κ ≈ 5) between the plates of a capacitor increases its capacitance by a factor of 5, since C = κε₀A/d, allowing more charge to be stored at the same voltage."

Dielectric breakdown

Phenomenon that occurs when an insulator becomes a conductor in a strong electrical field.

Example: "When the electric field between the capacitor plates exceeded 3 MV/m,          occurred and the air gap began conducting, discharging the capacitor in a visible spark."

Dielectric constant

Factor by which capacitance increases when a dielectric is inserted between the plates of a capacitor.

Example: "Inserting a glass dielectric with a          of κ = 5.6 between the plates of a 10 μF capacitor increased its capacitance to 56 μF, as given by C = κC₀."

Dielectric strength

Critical electrical field strength above which molecules in insulator begin to break down and the insulator starts to conduct.

Example: "Teflon has a          of approximately 60 MV/m, meaning the applied electric field must remain below this value to prevent the insulator from becoming conductive."

Difference of two vectors

Vector sum of the first vector with the vector antiparallel to the second.

Example: "To find the displacement from point B back to point A, you compute the difference A – B by adding vector A to the vector antiparallel to B, effectively reversing B's direction before summing."

Dimension

Expression of the dependence of a physical quantity on the base quantities as a product of powers of symbols representing the base quantities; in general, the dimension of a quantity has the form LaMbTcIdΘeNfJgLaMbTcIdΘeNfJg for some powers a, b, c, d, e, f, and g.

Example: "The          of force is [F] = M·L·T⁻², which can be verified from Newton's second law F = ma: mass has          M, and acceleration has          L·T⁻²."

Dimensionally consistent

Equation in which every term has the same dimensions and the arguments of any mathematical functions appearing in the equation are dimensionless.

Example: "The kinematic equation v² = v₀² + 2aΔx is          because every term has dimensions of (m/s)² = m²/s², confirming that the equation is physically valid."

Dimensionless

Quantity with a dimension of L0M0T0I0Θ0N0J0=1;L0M0T0I0Θ0N0J0=1; also called quantity of dimension 1 or a pure number.

Example: "The strain of a material (ΔL/L₀) is a          quantity because the units of length cancel, yielding a pure number that represents the fractional change in the object's length."

Diode

Nonohmic circuit device that allows current flow in only one direction.

Example: "A          in a circuit allows conventional current to flow only in the forward-bias direction (from anode to cathode), acting essentially as a one-way valve for electric charge."

Dipole

A molecule's lack of symmetrical charge distribution, causing one side to be more positive and another to be more negative.

Example: "A water molecule (H₂O) is an electric          because the oxygen atom pulls electron density away from the hydrogen atoms, creating a partial negative charge on one side and partial positive charges on the other."

Dipole moment

Property of a dipole; it characterizes the combination of distance between the opposite charges, and the magnitude of the charges.

Example: "A water molecule has a          of approximately 6.17 × 10⁻³⁰ C·m due to the separation of partial charges across its asymmetric O–H bonds, making it highly polar."

Direct current

(DC) the flow of electric charge in only one direction.

Example: "A 9 V battery drives          through a circuit, so charge carriers move consistently from the negative terminal through the external circuit to the positive terminal without reversing direction."

Direction angle

In a plane, an angle between the positive direction of the x-axis and the vector, measured counterclockwise from the axis to the vector.

Example: "A vector with components (3, 4) m makes a          of θ = arctan(4/3) ≈ 53° measured counterclockwise from the positive x-axis, which fully specifies its orientation in the plane."