Physics 1 glossary
Browse existing editorial definitions and examples, then follow deeper reading in the subject’s native course. Shared senses can belong to more than one subject. Historical source definitions and tables remain in the 242-entry Physics source glossary.
Physics 1 printables · Physics 1 interactive and source resources
94 of 94 editorial senses
Absolute pressure
Physics 1 · Physics 2 · Definition
Absolute pressure is pressure measured relative to a perfect vacuum.
It includes the atmospheric contribution that gauge pressure omits and is required in the ideal gas law.
For example, a tire’s absolute pressure is its gauge reading plus the surrounding atmospheric pressure.
Acceleration
Physics 1 · Physics 2 · Definition
Acceleration is the vector rate of change of velocity with time.
It can change an object’s speed, direction, or both, and it is measured in meters per second squared.
For example, a satellite moving at constant speed in a circular orbit accelerates toward the center.
Amplitude
Physics 1 · Physics 2 · Definition
Amplitude is the maximum magnitude of a repeating disturbance measured from its equilibrium value.
It describes the size of the oscillation rather than its frequency or propagation speed.
For example, pulling a spring-mounted mass farther from equilibrium increases its oscillation amplitude when it is released from rest.
Angular acceleration
Physics 1 · Physics 2 · Definition
Angular acceleration is the rate of change of angular velocity.
For a fixed axis its sign follows the chosen positive rotation direction, and its units are radians per second squared.
For example, a fan speeding up has angular acceleration, whereas one turning steadily does not.
Angular displacement
Physics 1 · Physics 2 · Definition
Angular displacement is the change in an object’s rotation angle about a specified axis.
Its sign follows the chosen rotation convention, and it is commonly measured in radians.
For example, a wheel can return to the same orientation after one turn while having an angular displacement of two pi radians.
Angular frequency
Physics 1 · Physics 2 · Definition
Angular frequency measures how rapidly the phase of a sinusoidal oscillation advances.
It equals two pi times the ordinary frequency and is measured in radians per second.
For example, two oscillators at the same ordinary frequency also have the same angular frequency even if their amplitudes differ.
Angular impulse
Physics 1 · Physics 2 · Definition
Angular impulse is the change in angular momentum caused by torque acting over time.
It is the signed area under a torque-versus-time graph about a consistent axis.
For example, applying a braking torque to a wheel for a longer interval changes its angular momentum more.
Angular momentum
Physics 1 · Physics 2 · Definition
Angular momentum describes motion about a specified point or axis.
For rigid rotation about a fixed principal axis it can be written as rotational inertia times angular velocity; a translating particle can also have angular momentum about a point.
For example, a ball moving past a pole has angular momentum about the pole even though the ball’s path is straight.
Angular velocity
Physics 1 · Physics 2 · Definition
Angular velocity describes the rate and direction of rotation about an axis.
For a fixed axis, a signed angular velocity is measured in radians per second, while its magnitude is angular speed.
For example, points on one rigid turntable share the same angular speed even though outer points have greater linear speeds.
Archimedes’ principle
Physics 1 · Physics 2 · Definition
Archimedes’ principle states that a submerged object’s buoyant-force magnitude equals the weight of the fluid it displaces.
Only the submerged volume contributes to displaced fluid for a partly floating object.
For example, a floating boat displaces enough water for the water’s weight to match the boat’s total weight.
Average velocity
Physics 1 · Physics 2 · Definition
Average velocity is the displacement over an interval divided by the elapsed time.
It is a vector and need not equal the average speed, which uses total distance.
For example, a runner who returns to the starting line has zero average velocity for the full lap.
Bernoulli’s equation
Physics 1 · Physics 2 · Definition
Bernoulli’s equation relates pressure, fluid speed, and elevation along a streamline in steady ideal flow.
Its usual form assumes an incompressible, nonviscous fluid and no added or removed mechanical energy along the path.
For example, in a horizontal pipe narrowing under those assumptions, higher flow speed accompanies lower pressure.
Buoyancy
Physics 1 · Physics 2 · Definition
Buoyancy is the net upward force arising from pressure differences over an object in a fluid under gravity.
Its magnitude equals the weight of the displaced fluid in the usual hydrostatic model.
For example, a fully submerged object can rise, sink, or remain suspended depending on how buoyancy compares with its weight.
Center of mass
Physics 1 · Physics 2 · Definition
The center of mass is the position obtained by weighting each part’s position by its mass.
Its motion represents the translational motion of the whole system under the net external force.
For example, adding a heavy object to one end of a light bar shifts the center of mass toward that end.
Centripetal acceleration
Physics 1 · Physics 2 · Definition
Centripetal acceleration is the inward acceleration component that changes the direction of motion along a curved path.
For circular motion its magnitude is speed squared divided by the circle’s radius.
For example, a car moving at constant speed around a bend still has centripetal acceleration.
Centripetal force
Physics 1 · Physics 2 · Definition
Centripetal force names the inward net-force component required for motion along a circular path.
It is supplied by actual interactions such as tension, friction, gravity, or normal forces rather than being an additional type of force.
For example, gravity supplies the centripetal force on a satellite in a circular orbit.
Coefficient of friction
Physics 1 · Physics 2 · Definition
A coefficient of friction is a dimensionless parameter describing friction between a pair of surfaces in a specified model.
The static coefficient sets a maximum friction magnitude, whereas the kinetic coefficient models friction during sliding.
For example, changing a shoe’s material or the floor condition can change the coefficient without changing the shoe’s mass.
Conservation of angular momentum
Physics 1 · Physics 2 · Definition
Angular momentum is conserved about a chosen axis when the net external angular impulse about that axis is zero.
Internal interactions can change the distribution of mass and the rotation rates of parts without changing the total.
For example, a rotating skater who pulls their arms inward can spin faster as their rotational inertia decreases.
Conservation of energy
Physics 1 · Physics 2 · Definition
Conservation of energy means total energy is unchanged when the full isolated system is considered.
Energy can transfer between objects or change form, so one selected energy store need not remain constant.
For example, friction can reduce a sliding block’s kinetic energy while increasing the thermal energy of the block and floor.
Conservative force
Physics 1 · Physics 2 · Definition
A conservative force does work that depends only on the starting and ending configurations.
A potential-energy function can describe it, and its work around a closed path is zero.
For example, near-Earth gravity does the same work between two heights whether a ball follows a vertical or a curved path.
Continuity equation
Physics 1 · Physics 2 · Definition
The continuity equation expresses conservation of mass in fluid flow.
For steady incompressible flow through one unbranched channel, cross-sectional area times average flow speed is constant.
For example, water moves faster through a narrower part of a pipe when the same volume passes each second.
Cross product
Physics 1 · Physics 2 · Definition
A cross product combines two vectors to form a vector perpendicular to both.
Its magnitude depends on both magnitudes and the sine of their included angle, while reversing input order reverses its direction.
For example, a force whose line of action passes through the pivot gives zero torque cross product about that pivot.
Displacement
Physics 1 · Physics 2 · Definition
Displacement is the vector change in position from the start of an interval to its end.
It depends on those endpoints rather than the length or shape of the path traveled.
For example, walking around a closed track and returning to the start gives zero displacement but a nonzero distance traveled.
Drag
Physics 1 · Physics 2 · Definition
Drag is a force from a fluid that opposes an object’s motion relative to that fluid.
Its dependence on speed, shape, and fluid properties varies with the physical regime.
For example, a parachute increases air drag by presenting a large area to the moving air.
Elastic collision
Physics 1 · Physics 2 · Definition
An elastic collision conserves the total kinetic energy of the colliding system.
Total momentum is also conserved when the system has negligible net external impulse, although each object’s momentum and energy can change.
For example, ideal gas atoms redistribute their speeds in elastic collisions without changing the pair’s total kinetic energy.
Equilibrium position
Physics 1 · Physics 2 · Definition
An equilibrium position is a position at which the net force in the modeled coordinate is zero.
In a stable oscillator, displacement to either side produces a restoring force back toward that position.
For example, a mass on a vertical spring oscillates about a position below the spring’s relaxed-length position because gravity shifts the balance.
Escape speed
Physics 1 · Physics 2 · Definition
Escape speed is the minimum launch speed needed to reach indefinitely large separation in a specified gravitational model without further propulsion.
Its value depends on the launch position and attracting mass, with air resistance and other bodies omitted in the simplest model.
For example, launching from a greater distance from the same spherical planet requires a smaller escape speed.
External force
Physics 1 · Physics 2 · Definition
An external force is exerted on part of a chosen system by something outside that system.
The sum of external forces determines the rate of change of the system’s total momentum.
For example, Earth’s gravitational force is external to a system consisting only of a falling ball.
Fluid
Physics 1 · Physics 2 · Definition
A fluid is a material that flows and continuously deforms under a sustained shear stress.
Liquids and gases are both fluids, although their compressibility and other properties can differ greatly.
For example, both water in a pipe and air flowing through a duct are fluids.
Force
Physics 1 · Physics 2 · Definition
A force describes an interaction that can change an object’s momentum.
It is a vector measured in newtons, so both size and direction matter when forces are added.
For example, a rope can pull a cart while the floor exerts friction in another direction.
Free fall
Physics 1 · Physics 2 · Definition
Free fall is motion in which gravity is the only significant force acting on the object.
An object can be in free fall while moving upward, downward, or sideways.
For example, a thrown ball is approximately in free fall after leaving the hand when air resistance is negligible.
Free-body diagram
Physics 1 · Physics 2 · Definition
A free-body diagram shows the external forces acting on one selected object or system.
Each arrow names a real interaction, and its direction is the direction of that force.
For example, a book resting on a desk has a downward gravitational force and an upward normal force; velocity is not an extra force arrow.
Frequency
Physics 1 · Physics 2 · Definition
Frequency is the number of complete repeating cycles per unit time.
It is measured in hertz, meaning cycles per second, and is the reciprocal of the period.
For example, a vibrating string with a higher frequency produces more cycles each second.
Gauge pressure
Physics 1 · Physics 2 · Definition
Gauge pressure is the difference between a system’s pressure and a specified surrounding reference pressure.
An ordinary pressure gauge usually uses local atmospheric pressure as its zero.
For example, a container open to the atmosphere has approximately zero gauge pressure while its absolute pressure is not zero.
Gravitational field
Physics 1 · Physics 2 · Definition
A gravitational field gives the gravitational force per unit mass at a location.
Its direction is the direction of the force on a positive test mass, and its units can be written as newtons per kilogram.
For example, near Earth the field points approximately downward, whether or not a ball is placed there.
Gravitational potential energy
Physics 1 · Physics 2 · Definition
Gravitational potential energy is energy associated with the relative positions of attracting masses.
Near Earth, changes can be approximated by mass times gravitational field strength times height change when that field is nearly constant.
For example, lifting a book increases the gravitational potential energy of the book–Earth system.
Gravity
Physics 1 · Physics 2 · Definition
Gravity is the attractive interaction between masses in the Newtonian model.
For spherical bodies or point-mass approximations, its strength decreases with the square of the separation between their centers.
For example, Earth’s gravity provides the inward force that keeps a satellite in orbit.
Hooke’s law
Physics 1 · Physics 2 · Definition
Hooke’s law models an ideal spring force as proportional to deformation and opposite in direction.
The deformation is measured from the spring’s relaxed length, and the law applies only within the spring’s approximately elastic linear range.
For example, doubling a small extension doubles the restoring-force magnitude of a spring that obeys this law.
Impulse
Physics 1 · Physics 2 · Definition
Impulse is the change in linear momentum produced by a force over a time interval.
It equals the signed vector area under a force-versus-time graph and is measured in newton-seconds.
For example, a padded landing spreads the stopping impulse over more time, reducing the average force for the same momentum change.
Incompressible fluid
Physics 1 · Physics 2 · Definition
An incompressible-fluid model treats density as constant despite pressure changes in the modeled situation.
This approximation often works for liquids over modest pressure ranges but is not a universal property of all fluids.
For example, water flowing through a narrowing pipe can often be treated as incompressible.
Inelastic collision
Physics 1 · Physics 2 · Definition
An inelastic collision does not conserve the colliding system’s total kinetic energy.
Momentum can still be conserved when the net external impulse is negligible, and total energy remains conserved when all stores are included.
For example, carts that latch together undergo a completely inelastic collision and convert some initial kinetic energy into other forms.
Inertia
Physics 1 · Physics 2 · Definition
Inertia is an object’s resistance to a change in its velocity.
Mass measures translational inertia, whereas rotational inertia also depends on how mass is distributed relative to an axis.
For example, a loaded cart accelerates less than an empty cart under the same net force.
Inertial frame
Physics 1 · Physics 2 · Definition
An inertial frame is a reference frame in which an object with no net external force moves at constant velocity.
Frames moving at constant velocity relative to an inertial frame are also inertial in the Newtonian model.
For example, a steadily moving train is approximately inertial, whereas a train accelerating out of a station is not.
Inertial mass
Physics 1 · Physics 2 · Definition
Inertial mass measures how strongly an object resists acceleration under a given net force.
It is the mass in Newton’s second law and is measured in kilograms.
For example, comparing accelerations under the same calibrated force lets an experiment compare two objects’ inertial masses.
Instantaneous velocity
Physics 1 · Physics 2 · Definition
Instantaneous velocity is the rate of change of position at a particular moment.
On a position-versus-time graph, its component is the slope of the tangent at that time.
For example, the velocity just before a ball lands differs from the average velocity of its entire flight.
Internal force
Physics 1 · Physics 2 · Definition
An internal force is an interaction between parts of a chosen system.
Newton’s third-law partners cancel in the total force sum for the whole system, although individual parts can accelerate.
For example, two skaters pushing each other exert internal forces when the two skaters are analyzed together.
Isolated system
Physics 1 · Physics 2 · Definition
An isolated system exchanges neither energy nor matter with its surroundings.
In a momentum problem, conservation of total momentum specifically requires zero net external impulse over the interval analyzed.
For example, two colliding carts can be treated as momentum-isolated horizontally when the external horizontal impulse is negligible.
Kinematics
Physics 1 · Physics 2 · Definition
Kinematics describes motion using position, velocity, acceleration, and time without first analyzing its forces.
The familiar constant-acceleration equations apply only over intervals in which that acceleration is constant.
For example, a ball falling near Earth with negligible air resistance can be modeled with constant vertical acceleration.
Kinetic energy
Physics 1 · Physics 2 · Definition
Kinetic energy is energy associated with motion relative to a chosen reference frame.
For a nonrelativistic translating object it is one half of its mass times speed squared.
For example, doubling a cart’s speed quadruples its translational kinetic energy when its mass stays fixed.
Kinetic friction
Physics 1 · Physics 2 · Definition
Kinetic friction acts between surfaces that slide relative to one another.
It opposes their relative slipping and is often modeled with magnitude equal to the kinetic-friction coefficient times the normal force.
For example, a rapidly moving belt can exert forward kinetic friction on a slower box sliding on it.
Lever arm
Physics 1 · Physics 2 · Definition
A lever arm is the perpendicular distance from a chosen rotation axis to a force’s line of action.
It determines the torque magnitude for a given force and need not equal the distance to the point of application.
For example, a force aimed directly toward a hinge has zero lever arm and produces no torque about that hinge.
Linear momentum
Physics 1 · Physics 2 · Definition
Linear momentum is a vector describing an object’s motion and equals mass times velocity in the nonrelativistic model.
The vector sum of momenta is conserved when the net external impulse on the system is zero.
For example, two identical carts moving equally fast in opposite directions have zero total linear momentum but nonzero total kinetic energy.
Magnitude
Physics 1 · Physics 2 · Definition
Magnitude is the nonnegative size of a vector quantity.
It does not specify direction, and it differs from a signed component.
For example, a westward velocity can have a negative x component while its speed, the velocity magnitude, stays positive.
Mass density
Physics 1 · Physics 2 · Definition
Mass density is mass per unit volume of a material or sample.
It is commonly measured in kilograms per cubic meter and can vary with temperature or pressure.
For example, equal-volume samples of water and oil generally have different masses because their densities differ.
Mechanical energy
Physics 1 · Physics 2 · Definition
Mechanical energy is the sum of the kinetic and potential energies included in a model.
It stays constant when transfers to or from other energy stores and across the chosen boundary are absent.
For example, a pendulum’s mechanical energy can remain approximately constant while energy shifts between motion and gravitational configuration.
Mechanical equilibrium
Physics 1 · Physics 2 · Definition
Mechanical equilibrium means there is no translational or angular acceleration for the system being considered.
For a rigid body, both the net external force and the net external torque must vanish.
For example, a stationary ladder supported against a wall requires both force balance and torque balance.
Mechanical work
Physics 1 · Physics 2 · Definition
Mechanical work is energy transferred by a force through displacement of its point of application.
For a constant force on a particle, it depends on the force component along the particle’s displacement, and it can be positive, negative, or zero.
For example, a magnetic force perpendicular to a particle’s displacement does zero work on that particle.
Net force
Physics 1 · Physics 2 · Definition
Net force is the vector sum of all forces acting on the object or system under consideration.
For constant mass in an inertial frame, it equals mass times acceleration.
For example, equal upward and downward forces give zero net force even though neither force is zero.
Nonconservative force
Physics 1 · Physics 2 · Definition
A nonconservative force can do work that depends on the path followed.
Its effects cannot be described by a single configuration-dependent potential energy for that interaction alone.
For example, sliding friction transfers more mechanical energy into thermal energy along a longer sliding path under the same conditions.
Normal force
Physics 1 · Physics 2 · Definition
A normal force is a contact force perpendicular to the local surface of contact.
Its magnitude is set by the motion and the other forces, so it need not equal the object’s weight.
For example, a wall’s normal force on a leaning ladder points horizontally rather than upward.
Orbital period
Physics 1 · Physics 2 · Definition
An orbital period is the time needed for one complete orbit.
In a two-body model it depends on the attracting mass and the orbit’s size rather than just the orbiting object’s mass.
For example, a larger circular orbit around the same planet has a longer orbital period.
Oscillation period
Physics 1 · Physics 2 · Definition
An oscillation period is the time required for one complete repeating cycle.
It is the reciprocal of frequency and is measured in seconds.
For example, measuring the time for several pendulum swings and dividing by the number of cycles estimates the period.
Oscillation phase
Physics 1 · Physics 2 · Definition
Phase specifies the position within a repeating oscillation cycle.
A phase difference tells how much one oscillation leads or lags another at a chosen place and time.
For example, two sinusoidal waves half a cycle out of phase can cancel when their amplitudes are equal.
Parallel-axis theorem
Physics 1 · Physics 2 · Definition
The parallel-axis theorem relates rotational inertia about a center-of-mass axis to inertia about a parallel displaced axis.
The displaced-axis value is the center-of-mass value plus total mass times the squared separation of the axes.
For example, a uniform rod has greater rotational inertia about one end than about a parallel axis through its middle.
Pendulum
Physics 1 · Physics 2 · Definition
A pendulum is a system that swings about a support under a restoring torque.
A simple pendulum approximates a small mass on a light string and follows simple harmonic motion only for sufficiently small angles.
For example, a short string pendulum completes small swings more quickly than a longer one under the same gravitational field.
Physical system
Physics 1 · Physics 2 · Definition
A physical system is the object or collection of objects chosen for an analysis.
Its boundary determines which forces and energy transfers count as internal or external.
For example, friction between a block and a floor is an external interaction for the block alone but internal when both are included.
Potential energy
Physics 1 · Physics 2 · Definition
Potential energy describes energy associated with the configuration of interacting parts of a system.
Its numerical zero is a chosen reference, while differences in potential energy determine physical energy changes.
For example, separating Earth and a ball changes their gravitational potential energy even though the energy belongs to their interaction.
Power
Physics 1 · Physics 2 · Definition
Power is the rate at which energy is transferred or converted.
It is measured in watts, with one watt equal to one joule per second.
For example, two motors can lift the same load through the same height but have different average powers if they take different times.
Pressure
Physics 1 · Physics 2 · Definition
Pressure is the normal force per unit area exerted on a surface.
It is a scalar measured in pascals, with one pascal equal to one newton per square meter.
For example, a gas exerts pressure throughout its volume through many microscopic collisions, even when its bulk motion is zero.
Projectile motion
Physics 1 · Physics 2 · Definition
Projectile motion describes an object after launch when gravity is the only significant force in the chosen model.
Near Earth, horizontal and vertical motion can be analyzed separately using the same time interval and approximately constant downward acceleration.
For example, a ball rolling off a table continues horizontally while its downward velocity increases.
Radian
Physics 1 · Physics 2 · Definition
A radian is an angle measure defined by arc length divided by radius.
One complete turn is two pi radians, and angle formulas connecting linear and rotational motion use this measure.
For example, an arc whose length equals the circle’s radius subtends one radian at the center.
Reference frame
Physics 1 · Physics 2 · Definition
A reference frame specifies the observer and coordinates used to describe positions and motion.
Different observers can assign different velocities to the same object.
For example, a seated passenger is at rest relative to a train but moving relative to the station.
Restoring force
Physics 1 · Physics 2 · Definition
A restoring force points toward an equilibrium position when an object is displaced from it.
Simple harmonic motion requires the net restoring force to be proportional to displacement and opposite in direction.
For example, a compressed ideal spring pushes its attached object back toward the spring’s relaxed length.
Resultant vector
Physics 1 · Physics 2 · Definition
A resultant vector is the vector sum of two or more vectors.
Its components are the sums of the corresponding components of the vectors being combined.
For example, two equal forces in opposite directions have a zero resultant even though both forces are present.
Right-hand rule
Physics 1 · Physics 2 · Definition
A right-hand rule is a convention for determining the direction of a vector cross product or a current-produced magnetic field.
The chosen gesture must use the correct input vectors in their correct order, with reversal when a negative charge requires it.
For example, the thumb-and-curl rule around a straight wire uses conventional current as the thumb direction.
Rolling without slipping
Physics 1 · Physics 2 · Definition
Rolling without slipping means the point of contact has no instantaneous relative motion along the contacting surface.
For a wheel rolling on a stationary surface, the center-of-mass speed equals angular speed times radius.
For example, a wheel rolling smoothly along a road has a momentarily stationary contact point while its top moves faster than its center.
Rotational equilibrium
Physics 1 · Physics 2 · Definition
Rotational equilibrium means the net external torque about the chosen axis is zero.
A rigid body’s angular velocity then stays constant when its rotational inertia is fixed; it need not be at rest.
For example, opposing torques can balance on a wheel that is already rotating steadily.
Rotational inertia
Physics 1 · Physics 2 · Definition
Rotational inertia measures how strongly a mass distribution resists a change in angular velocity about a specified axis.
Mass farther from that axis contributes more strongly because each contribution depends on squared distance.
For example, moving small masses outward along a rotating rod increases its rotational inertia without changing its total mass.
Rotational kinetic energy
Physics 1 · Physics 2 · Definition
Rotational kinetic energy is the kinetic energy associated with rotation about an axis.
For a rigid body about a fixed axis it is one half of rotational inertia times angular speed squared.
For example, a rolling wheel can possess both translational kinetic energy of its center of mass and rotational kinetic energy about that center.
Scalar
Physics 1 · Physics 2 · Definition
A scalar is a quantity described by a value and unit without a spatial direction.
A scalar can have a sign when its definition or reference permits one; scalar does not mean always positive.
For example, mass is a scalar, whereas the velocity of that mass also needs a direction.
Simple harmonic motion
Physics 1 · Physics 2 · Definition
Simple harmonic motion occurs when the net restoring force is proportional to displacement from equilibrium and points in the opposite direction.
The resulting position varies sinusoidally with time in the ideal model.
For example, a mass attached to an ideal spring can execute simple harmonic motion when damping is negligible.
Spring constant
Physics 1 · Physics 2 · Definition
A spring constant measures the stiffness of a spring within its approximately linear range.
Its units are newtons per meter, and a larger value means more force is needed for the same deformation.
For example, two springs stretched by the same distance exert different forces if one is stiffer.
Spring potential energy
Physics 1 · Physics 2 · Definition
Spring potential energy is energy stored in an ideal spring’s deformation from its relaxed length.
It is proportional to the square of deformation, so equal extension and compression magnitudes store equal energy.
For example, compressing a spring before releasing a toy transfers energy that can later become kinetic energy.
Static friction
Physics 1 · Physics 2 · Definition
Static friction opposes the tendency for relative sliding between surfaces that are not sliding at their contact.
In the simple model it adjusts up to a maximum set by the coefficient of static friction and normal force.
For example, static friction can push a walking person forward when the foot pushes backward on the ground.
Streamline
Physics 1 · Physics 2 · Definition
A streamline is a curve tangent to the local fluid velocity at each point at one instant.
In steady flow its shape stays fixed and fluid particles follow it, while in changing flow a streamline need not be a particle’s full path.
For example, streamline arrows around a smooth obstacle show the local direction of the passing fluid.
Superposition
Physics 1 · Physics 2 · Definition
Superposition means adding the separate contributions to obtain a total response in a linear model.
Vector fields add vectorially, scalar potentials add algebraically, and wave disturbances add with their signs at each place and time.
For example, equal but opposite electric-field contributions can give zero net field at one point while both sources remain present.
Tension
Physics 1 · Physics 2 · Definition
Tension is a pulling force transmitted through a stretched rope, string, or similar connector.
It acts along the connector away from the object it pulls, and an ideal massless rope has the same tension throughout an uninterrupted segment.
For example, a rope supporting an accelerating load can have a tension different from the load’s weight.
Torque
Physics 1 · Physics 2 · Definition
Torque describes a force’s turning effect about a chosen axis or point.
Its magnitude is force times the perpendicular lever arm, and its direction or sign describes the rotation tendency.
For example, pushing near the handle of a door produces more torque than the same perpendicular push near the hinge.
Unit vector
Physics 1 · Physics 2 · Definition
A unit vector has magnitude one and specifies a direction.
Multiplying it by a signed component gives the vector contribution along that direction.
For example, the Cartesian unit vectors identify the positive x, y, and z directions.
Vector
Physics 1 · Physics 2 · Chemistry · Definition
A vector is a quantity with a magnitude and a direction, represented by an arrow or by components along chosen axes.
Vectors add by adding corresponding components rather than simply adding their magnitudes.
For example, an eastward displacement followed by a northward displacement produces a resultant pointing northeast.
The zero vector has zero magnitude and no unique direction.
Vector component
Physics 1 · Physics 2 · Definition
A vector component describes the part of a vector along a chosen axis.
Its signed value changes when the axes change, even though the physical vector remains the same.
For example, a diagonal launch velocity can be resolved into horizontal and vertical components that share the same elapsed time.
Velocity
Physics 1 · Physics 2 · Definition
Velocity describes how position changes with time and includes direction.
Instantaneous velocity describes one moment, while average velocity is displacement divided by elapsed time.
For example, a car turning a corner can change velocity while maintaining the same speed.
Viscosity
Physics 1 · Physics 2 · Definition
Viscosity measures a fluid’s resistance to relative motion between neighboring layers.
Viscous effects can dissipate mechanical energy and alter the velocity profile of flowing fluid.
For example, honey flows more reluctantly than water under comparable conditions because it is more viscous.
Weight
Physics 1 · Physics 2 · Definition
Weight is the gravitational force exerted on an object by a specified attracting body.
Near Earth’s surface its magnitude is approximately mass times the local gravitational field strength, and it is measured in newtons.
For example, an astronaut has less weight on the Moon while retaining the same mass.