AP Physics 1 Glossary 2027
A concept dictionary for unfamiliar physics terms. Every entry defines the term on this page first, gives a physical example when available, and then links to the relevant topic for deeper study.
What is in the AP Physics 1 glossary?
The searchable glossary defines 259 AP Physics 1 terms on the page, gives a physical example, and links each term to the deeper relevant lesson without forcing the student to click away just to understand the definition.
- 259 unique terms.
- Same-page definition first.
- Direct links to the relevant topic lesson.
A system cannot exert a net force on itself
Only interactions with the environment contribute to the net external force on the chosen system; internal force pairs cancel in the whole-system force sum.
Acceleration
Acceleration is the vector rate at which velocity changes with time. It can change speed, direction, or both.
Acceleration phase
Acceleration is opposite in sign to position: a=−ω²x.
Amplitude
Maximum magnitude of displacement from equilibrium.
Amplitude-energy relation
For spring SHM, total energy scales with A².
Angular acceleration
Rate of change of angular velocity.
Angular graphs
Slope and area relationships mirror translational kinematics.
Angular impulse
Torque acting over time changes angular momentum.
Angular momentum
A rotational momentum quantity whose change equals angular impulse about the chosen axis.
Angular position/displacement
Angular position locates rotational orientation; angular displacement is its signed change.
Angular velocity
Rate of change of angular position.
Angular vs linear conservation
A system can have one conserved quantity under conditions where the other changes, depending on external force and torque.
Angular-speed squared dependence
K_rot grows with ω².
Apparent weight
Apparent weight is the support force measured by a scale or felt by a supported person, often the normal force; it can differ from mg when acceleration is present.
Apparent weight in fluid
Scale/support force can be reduced by buoyant force.
Arc length
A point at radius r travels arc length s=rθ for angular displacement θ in radians.
Archimedes principle
Buoyant force equals the weight of displaced fluid.
Atmospheric pressure
Fluid surfaces open to air have atmospheric pressure acting on them.
Average density
Composite/porous objects can be described by total mass divided by total external volume.
Average force and collision time
For a fixed momentum change, increasing stopping time reduces average force magnitude.
Average power
Energy transferred per elapsed time.
Axis choice
For equilibrium, torque sum is zero about any axis; choosing an axis through unknown forces can simplify equations.
Axis dependence
Torque depends on the chosen rotation axis.
Balanced on one axis, unbalanced on another
Force balance is evaluated independently by axis; zero net force on one axis does not require zero net force on every axis.
Banked curves and conical pendulums
Real force components can supply the inward net force: a banked road uses a component of the normal force, while a conical pendulum uses a horizontal component of tension.
Bernoulli energy
Pressure energy, kinetic energy per volume, and gravitational potential energy per volume trade along ideal flow.
Buoyant force
Net upward force from fluid pressure differences on an immersed object.
Center of gravity near Earth
Weight can be represented as acting at the center of mass for uniform g.
Center of mass
The center of mass is the mass-weighted average position of a system. Its motion represents the translational motion of the system as a whole.
Center-of-mass connection
Total momentum relates to total mass times center-of-mass velocity.
Centripetal (radial) acceleration
Centripetal acceleration is the inward acceleration required to curve the velocity vector in circular motion; for speed v and radius r its magnitude is v²/r.
Centripetal acceleration
Always points toward the center of curvature.
Centripetal force
“Centripetal force” is not a new interaction; it is the net inward radial component of real forces that produces centripetal acceleration.
Change in momentum
Impulse equals final momentum minus initial momentum.
Changing rotational inertia
If L is conserved, decreasing I increases |ω| and increasing I decreases |ω|.
Choose useful axes after the diagram
Axes can be chosen to simplify force components—often parallel to acceleration or parallel/perpendicular to an incline—but the FBD still shows whole forces first.
Circular motion
Circular motion is motion along a circular path. Even at constant speed, the velocity direction changes, so the object has inward radial acceleration.
Circular orbit
A circular orbit is continuous free fall in which gravity supplies the inward acceleration while tangential velocity carries the object around the central body.
Circular orbit / Kepler’s third law
For a satellite in a circular orbit, gravitational attraction alone supplies the centripetal acceleration; orbital period grows with orbital radius for a fixed central mass.
Coefficients depend on surface materials
μ_s and μ_k describe the interacting surface pair; typically μ_s is greater than μ_k for that pair.
Combined kinetic energy
Rolling object has translational and rotational kinetic energy.
Component equations
Apply the law independently along perpendicular axes.
Conservative force
A force for which work can be represented by a potential-energy change and is path independent between fixed endpoints.
Conservative interaction
For a conservative force, work by the force is related to the negative change in potential energy.
Constant acceleration
Constant acceleration means the acceleration vector remains constant during the modeled interval, allowing the standard constant-acceleration equations.
Constant angular velocity
Zero net torque means α=0, not necessarily ω=0.
Constant velocity
Velocity stays unchanged in both magnitude and direction.
Contact area in the simple model
For the AP ideal dry-friction model, friction magnitude does not depend on the apparent area of contact when N and the surface pair are unchanged.
Contact vs long-range interaction
Contact forces require touching surfaces; in AP Physics 1, gravitational force is the long-range interaction used in this unit.
Continuity
For steady incompressible flow, volume flow rate is constant along a tube.
Coordinate sign
A coordinate sign is the plus or minus label assigned to a vector component after a positive axis has been chosen; it represents direction, not whether speed is increasing.
Damping
Real dissipative forces reduce mechanical energy and amplitude over time.
Density
Mass contained per unit volume.
Depth dependence
Pressure increases with vertical depth in a uniform fluid.
Different objects
The two third-law forces never act on the same object.
Displacement
Displacement is the vector change in position, Δx=x_f−x_i; it depends only on initial and final position, not on path length.
Efflux/jet reasoning
Pressure or height differences can drive flow and determine speed.
Elastic collision
Both system momentum and kinetic energy are conserved.
Elastic potential energy
A deformed ideal spring stores energy relative to its relaxed length.
Elliptical orbits
In an elliptical orbit, orbital radius and speed change while total mechanical energy and angular momentum remain constant for the isolated two-body model.
Energy accounting
Rotational kinetic energy participates in conservation-of-energy analysis.
Energy at amplitude
At turning points speed is zero, so kinetic energy is zero and potential energy is maximum.
Energy at equilibrium
At equilibrium potential energy is minimum (for chosen reference) and speed/kinetic energy are maximum.
Energy bar/flow representations
Bar charts and flow diagrams track where energy is stored and transferred.
Energy landscape reasoning
A system tends to accelerate in the direction of decreasing potential energy when that interaction dominates.
Equilibrium
A state in which the relevant net force and, when rotational equilibrium is required, net torque are zero.
Equilibrium position
Position where net force is zero.
Equivalence principle
Locally, an observer in a uniformly accelerating noninertial frame can experience apparent weight effects that are indistinguishable from those associated with a gravitational field.
Escape and bound energy
With gravitational potential energy defined as zero at infinity, a bound orbit has negative total mechanical energy; escape corresponds to reaching infinity with nonnegative total energy.
Exchange with the environment
A chosen system can exchange energy or mass with its environment; the boundary determines what counts as a transfer.
Explosion/recoil
An interaction can convert internal energy to kinetic energy while conserving momentum.
External conditions can change substructure
A system’s internal configuration can change when external variables or interactions change, so the one-object model must be reconsidered when substructure affects the question.
External force
An external force is a force exerted on the chosen system by an object outside the system boundary.
External impulse
External forces can change total system momentum.
External interaction
An interaction on the system from an object outside its boundary.
External torque on system
Internal torque pairs do not change total angular momentum of a suitably chosen system; rotational dynamics use net external torque.
External work
Energy can cross a chosen system boundary through work by an external force.
Floating equilibrium
A freely floating object at rest has buoyant force equal to its weight.
Fluid pressure direction
At a point in a fluid at rest, pressure acts normal to surfaces in all directions.
Force
A force is a vector interaction exerted by one object on another that can contribute to changing the object’s velocity. Forces are measured in newtons.
Force and velocity
Mechanical power from a force depends on the component of force along velocity.
Force as an interaction
A force exists because two objects or systems interact; naming a force correctly identifies both the object exerting the force and the object receiving it.
Force components
Force components are projections of force vectors onto chosen perpendicular axes so Newton’s second law can be applied separately in each direction.
Force vector
A force vector represents both the magnitude and direction of one physical interaction acting on the chosen object or system.
Force-position graph
For spring SHM, F versus x is a straight line with negative slope −k.
Force–position graph
The signed area under an F-parallel versus position graph equals work.
Force–time graph
Signed area under an F-versus-time graph gives impulse.
Free fall/orbit
Objects can feel weightless while gravity still acts strongly.
Free-body diagram
A free-body diagram is a representation of one chosen object or system showing every external force acting on it as a vector and excluding forces it exerts on other objects.
Frequency
Cycles per second in hertz.
Friction
Contact force parallel to the interface that opposes relative slipping or its tendency.
Gravitational field
Gravitational field at a point is gravitational force per unit test mass, g=F_g/m; it points in the direction a small positive test mass would accelerate.
Gravitational force
Gravitational force is the attractive interaction between masses, directed along the line joining their centers; for point masses or spherical bodies its magnitude is Gm₁m₂/r².
Gravitational potential energy near Earth
For small height changes near Earth, Earth–object gravitational potential energy changes with vertical position.
Gravity as centripetal force
For a circular orbit, gravitational force points toward the central body and supplies inward acceleration.
Gravity near Earth
Near Earth’s surface, over height changes small compared with Earth’s radius, the gravitational field is approximately uniform and free objects have nearly constant downward acceleration g.
Hooke’s law
Hooke’s law models an ideal spring in its linear range as F_s=−kΔx, where Δx is signed deformation measured from relaxed length and k is the spring constant.
Horizontal and vertical projectile motion
In ideal projectile motion, the horizontal component has zero acceleration while the vertical component has constant downward gravitational acceleration; the two components are solved separately but use the same time.
Ideal fluid
A model fluid treated as incompressible and nonviscous for continuity/Bernoulli reasoning.
Ideal pulley
An ideal pulley has negligible mass and negligible axle friction, so it does not require a tension difference to rotationally accelerate the pulley.
Ideal tension
A massless nonstretching string over an ideal pulley has the same tension magnitude throughout.
Ideal-flow assumptions
Bernoulli/continuity models assume conditions such as steady, incompressible, negligible-viscosity flow along a streamline.
Impulse
Impulse measures accumulated force over time.
Inelastic collision
Momentum can be conserved while some kinetic energy becomes thermal, sound, deformation, or internal energy.
Inertia
Inertia is the tendency of an object to resist changes in its velocity; mass quantifies translational inertia.
Inertial frame
An inertial frame is a reference frame in which an object with zero net external force moves with constant velocity, so Newton’s first law holds without fictitious forces.
Inertial vs gravitational mass
Inertial mass controls resistance to acceleration; gravitational mass controls gravitational interaction strength, and experiments find them equivalent.
Instantaneous power
The rate of energy transfer at a particular instant.
Instantaneous value
An instantaneous motion value is the value at a particular moment, obtained conceptually as the time interval used for an average becomes extremely small.
Interaction pair
Two forces from one interaction, equal in magnitude and opposite in direction.
Internal forces
Forces between objects inside the system cannot change total system momentum by themselves.
Internal interaction
An interaction between objects that are both inside the chosen system.
Internal structure matters when relevant
A complex system may be treated as one object only when its internal arrangement/interactions do not affect the question being asked.
Internal torque transfer
Internal torques can exchange angular momentum among parts without changing total system L.
Internal-force cancellation
When both interacting objects are inside one system, each pair cancels in the whole-system force sum.
Inverse-square dependence
Force weakens as 1/r² with center-to-center separation.
Inward net force
“Centripetal force” is not a new force; real forces/components sum inward.
Isolated-system model
Momentum is conserved when external impulse is zero/negligible.
Kepler’s third law for circular orbits
For objects orbiting the same central mass, orbital period squared is proportional to orbital radius cubed, T²∝R³; larger circular orbits have longer periods.
Kinematic constraint
Center-of-mass speed and angular speed satisfy v_cm=Rω.
Kinetic energy
Energy associated with motion; translational kinetic energy uses the speed of the object or system center of mass.
Kinetic friction
Kinetic friction acts when surfaces slide relative to each other; in the ideal model its magnitude is f_k=μ_kN and its direction opposes relative sliding at the contact.
Kinetic-energy test
Comparing total K before and after distinguishes elastic from inelastic when momentum is conserved.
Lever arm
A force farther from the axis usually produces greater torque.
Line of centers
For point masses or spherically symmetric objects, the gravitational interaction acts along the line joining their centers of mass; each body experiences the force toward the other body.
Linear force graph
Within the ideal range, spring force versus signed deformation is linear with slope −k when the positive deformation axis is defined consistently.
Magnitude
Magnitude is the nonnegative size of a quantity, independent of its vector direction.
Mass dependence
At the same speed, the more massive object has more translational kinetic energy.
Mass distribution
Mass farther from the axis contributes more strongly to I.
Mass resists acceleration
For the same net force, a larger mass has smaller acceleration.
Mass-weighted average
A mass-weighted average gives each location influence in proportion to the mass located there, so heavier parts pull the center of mass closer to themselves.
Massive-string boundary
For a string, cable, or chain with nonnegligible mass, AP Physics 1 expects qualitative reasoning about changing tension rather than unrestricted quantitative tension distributions.
Maximum static friction
Maximum static friction is the largest possible static-friction magnitude in the ideal model, f_s,max=μ_sN; actual static friction can be smaller.
Mechanical energy
Kinetic plus relevant potential energies are conserved only when no nonconservative transfer changes mechanical energy.
Microscopic origin of contact forces
Normal force, friction and tension are macroscopic models of electromagnetic interactions between atoms and molecules at contact.
Microscopic structure
Density reflects particle masses and spacing at the microscopic level.
Momentum vs kinetic energy
Momentum depends linearly on speed; kinetic energy depends on speed squared and is scalar.
Motion graphs
Motion graphs represent position, velocity, or acceleration as a function of time so that shape, slope, and signed area encode physical motion.
Multiple torques
Use signed sum of all external torques.
Near-Earth field value
When the gravitational field does not change appreciably over the motion, AP Physics 1 commonly uses g ≈ 10 N/kg, numerically equal to about 10 m/s² for a freely falling object.
Negative work
A force does negative work when its parallel component opposes displacement.
Net external force
Net external force is the vector sum of all external forces acting on the chosen system. It is a result of adding forces, not an additional force to draw.
Net force
Net force is the vector sum of all forces included in the force model for the chosen object or system; in Newton’s second law the relevant sum is the net external force.
Net force sets acceleration
Acceleration points with the vector sum of external forces.
Net torque
Rotational response depends on the sum of torques.
Net torque causes angular acceleration
A nonzero net torque changes angular velocity.
Newton-third-law interaction pair
A third-law pair consists of the two forces produced by the same interaction, one on each interacting object. They never cancel on a one-object free-body diagram because they act on different objects.
Newton’s first law
In an inertial frame, an object with zero net external force maintains constant velocity, including the special case of remaining at rest.
Newton’s second law
Newton’s second law states that the vector sum of external forces on a system equals its mass times the acceleration of its center of mass: ΣF_ext = ma_cm for a constant-mass system.
Newton’s third law
When object A exerts a force on object B, object B simultaneously exerts a force of equal magnitude and opposite direction on object A. The two forces act on different objects.
No external torque condition
Conservation requires negligible net external torque about the chosen axis.
Normal force
Normal force is the contact force a surface exerts perpendicular to itself. Its magnitude is determined by the actual perpendicular dynamics and is not automatically equal to mg.
Normal-force dependence
Changing perpendicular forces changes N and therefore friction magnitudes.
Object momentum
Momentum combines mass and velocity.
Orbital period
Farther circular orbits take longer to complete.
Orbital speed vs radius
For circular orbit around fixed central mass, farther orbits have lower speed.
Particle angular momentum
A moving particle can have angular momentum about an origin depending on r and perpendicular momentum.
Particle contribution
A point mass contributes mr².
Pendulum dependence
For small angles, T depends on length and g, not bob mass.
Perfectly inelastic collision
Objects stick and share one final velocity.
Period
Time for one full cycle.
Period and frequency
Period T is the time for one complete cycle or revolution; frequency f is cycles per second, with f=1/T.
Periodic vs SHM
All SHM is periodic, but not all periodic motion satisfies a∝−x.
Perpendicular component
Only the force component perpendicular to the radius contributes to torque.
Phase/quarter cycles
Key quantities repeat in a predictable sequence every T/4.
Position
Position specifies where an object is relative to a chosen origin and coordinate axis.
Position, displacement, velocity and acceleration
Position locates an object relative to an origin; displacement is the vector change in position; velocity is the rate of change of position; acceleration is the rate of change of velocity.
Position-time sinusoid
Position varies periodically between ±A.
Positive work
A force does positive work when its component along the displacement points with the displacement.
Positive/negative rotational work
Torque aligned with angular displacement does positive work; opposing torque does negative work.
Power in rotation
Rotational power can be related to torque and angular speed.
Power units
One watt equals one joule per second.
Pressure definition
Pressure distributes normal force over area.
Projectile
An object whose post-launch motion is modeled with gravity as the only force when air resistance is neglected.
Projectile motion
Projectile motion is two-dimensional motion of an object that, after launch, is acted on only by gravity in the ideal AP model. Horizontal and vertical motions share the same elapsed time but have different accelerations.
Proportionality
In ideal SHM, restoring acceleration magnitude grows linearly with displacement magnitude.
Rate of change
A rate of change measures how much one quantity changes per unit change of another; in kinematics the independent variable is usually time.
Reciprocal relationship
Period and frequency describe the same cycle rate in inverse ways: f=1/T and T=1/f.
Recoil/explosion
Objects can gain opposite momenta while total remains fixed.
Reference frame
A reference frame is the coordinate system and observer relative to which position and velocity are measured.
Reference level
The zero of potential energy can be chosen for convenience; physically meaningful predictions use differences.
Relative slipping
Relative slipping means the two contacting surfaces move relative to each other at the contact point; friction direction is determined by actual or impending relative slip, not simply by center-of-mass velocity.
Relative velocity
Relative velocity is the velocity of one object as measured from another chosen object or frame. In one dimension, v_A/B=v_A−v_B using one consistent sign convention.
Relaxed length
Relaxed length is the spring length at which its deformation is zero and an ideal spring exerts zero Hooke-law force.
Relaxed length vs system equilibrium
Relaxed length is a property of the spring; equilibrium is where the net force on the attached object/system is zero and can be shifted by other forces.
Rest as constant velocity
Zero velocity is one valid constant velocity.
Restoring direction
In the Hooke’s-law model, the spring’s own force opposes the signed change in spring length from relaxed length. The current CED also describes spring force as directed toward the object–spring system equilibrium; in multi-force setups, keep that wording distinct from the net force that determines mechanical equilibrium.
Restoring force
A force directed toward equilibrium after displacement.
Rigid-body angular momentum
For fixed-axis rigid rotation, L=Iω along the rotation axis direction.
Rigid-body rotation
All points of a rigid body share the same angular displacement, angular velocity, and angular acceleration about the axis.
Rolling connection preview
For rolling without slipping, translational center-of-mass speed connects to angular speed by v_cm=Rω.
Rolling while slipping
An object can translate and rotate while the contact point slips relative to the surface; then the no-slip constraint v_cm=Rω does not apply.
Rolling without slipping
The point of contact is instantaneously at rest relative to the surface for ideal no-slip rolling.
Rotational analog of mass
I plays in rotational dynamics a role analogous to mass in translation.
Rotational inertia resists angular acceleration
For the same net torque, larger I means smaller α.
Rotational kinetic energy
A rotating object stores kinetic energy because its mass elements move around an axis.
Rotational work
A torque acting through angular displacement transfers energy.
Rotational-inertia dependence
For equal ω, larger I means larger K_rot.
Same work, different time
Doing the same work in less time requires greater average power.
Same-depth pressure
In a connected static fluid of uniform density, points at the same depth have equal pressure regardless of container shape.
Scalar
A quantity described by magnitude only.
Scalar and vector
A scalar is fully described by magnitude alone. A vector requires both magnitude and direction.
Scalar energy
Kinetic energy has magnitude but no direction, even though velocity is a vector.
Shape comparison
Different shapes with equal M and R can have different I because mass is distributed differently.
Signed area on a motion graph
Signed area counts regions above the time axis as positive and below as negative; area under v–t gives displacement and under a–t gives change in velocity.
Signed vector addition
In one dimension, vector addition is ordinary signed addition after opposite directions are assigned opposite signs.
Sinking/rising
If net force is downward, object accelerates downward; if upward, it accelerates upward (ignoring/including drag as specified).
Slope on a motion graph
Slope is change in the vertical-axis quantity divided by change in time; x–t slope gives velocity and v–t slope gives acceleration.
Specific comparison
Relative density helps predict buoyancy trends when compared with fluid density.
Speed-squared dependence
Because K is proportional to v², doubling speed multiplies kinetic energy by four.
Spring constant k
Measures stiffness: change in force magnitude per unit deformation in the linear Hooke’s-law region.
Spring force
Spring force is the restoring contact force an ideal spring exerts when stretched or compressed from its relaxed length; it points in the direction that tends to reduce the deformation.
Spring-mass dependence
T increases with mass and decreases with spring stiffness.
Spring-system equilibrium
Spring-system equilibrium is the position where the net force on the attached object/system is zero; it need not coincide with the spring’s relaxed length.
Static equilibrium
For an object completely at rest, both net force and net torque are zero.
Static friction
Static friction acts between surfaces that are not slipping relative to each other and adjusts to the value needed to prevent slipping, up to a maximum.
Static friction role
Static friction can supply torque without necessarily dissipating mechanical energy.
Streamline
A curve tangent to the local fluid velocity in steady flow.
Symmetry and center of mass
For a uniform highly symmetric object, the center of mass lies on every line or plane of symmetry, often allowing it to be located without summing particles.
System
A system is the object or group of objects deliberately chosen for analysis. The system boundary determines which interactions are internal and which are external.
System boundary
A system boundary is the conceptual boundary separating the chosen system from its environment. Forces crossing that boundary are external to the system.
System center-of-mass motion
For an extended system, translational kinetic energy refers to whole-system motion and is distinct from rotational or internal energy.
System choice
A multi-object system can eliminate internal forces from the equation.
System momentum
Total system momentum is the vector sum of momenta of all objects.
System properties and interactions
Macroscopic system behavior depends on interactions among constituent objects; individual parts can behave differently from the system as a whole.
Tangential acceleration
Tangential acceleration is the component of acceleration tangent to a circular path that changes speed, while radial acceleration changes direction.
Tangential speed
Linear speed of a point is v=rω.
Tangential velocity
Velocity is tangent to the path at each instant.
Tension
Tension is the pulling force transmitted by a taut string, rope, or cable. In an ideal massless string over ideal supports, the tension magnitude is uniform.
Thermal/internal energy
Friction can transform organized mechanical energy into thermal/internal energy without violating total-energy conservation.
Torque sign
Clockwise and counterclockwise torques can be assigned opposite signs.
Torque–angle graph
Area under τ versus θ gives rotational work.
Torque–time graph
Signed area under τ versus time equals angular impulse.
Torricelli’s theorem
A result for efflux speed from an ideal-fluid opening, connecting pressure/height energy to kinetic energy.
Total acceleration in nonuniform circular motion
When speed changes on a curved path, the acceleration is the vector sum of perpendicular inward centripetal and tangential components.
Total energy conservation
The total energy of an isolated system remains constant even as forms change.
Total mechanical energy
Ideal oscillator’s K+U remains constant.
Translation plus rotation
A rigid body can have center-of-mass acceleration and angular acceleration simultaneously.
Translational acceleration
Translational acceleration is the acceleration of an object or system as a whole—equivalently, for an extended system, the acceleration of its center of mass. It describes change in the system’s translational velocity and is distinct from angular acceleration.
Translational equilibrium
Translational equilibrium means the net external force is zero, so acceleration is zero and velocity is constant; the object may be at rest or moving uniformly.
Translational motion
Translational motion is motion of an object or system as a whole from one location to another, tracked by the position, velocity and acceleration of a representative point such as its center of mass.
Translational motion of a system
Translational motion is motion of the system as a whole, represented by changes in the center-of-mass position and therefore its center-of-mass velocity and acceleration.
Uniform material
For uniform density, mass is proportional to volume.
Universal attraction
Every pair of masses exerts equal-and-opposite gravitational forces.
Vector
A vector is a physical quantity with a magnitude and a direction; along one axis its direction can be encoded by a plus or minus sign.
Vector components
Vector components are perpendicular parts of one vector whose vector sum reproduces the original vector.
Vector conservation
Momentum conservation must preserve direction/sign or components.
Vector direction
Momentum points in the same direction as velocity for positive mass.
Vector impulse
Impulse direction matches the direction of momentum change.
Velocity
Velocity is the directed rate at which position changes with time. Average velocity is Δx/Δt; instantaneous velocity describes that rate at one moment.
Velocity phase
Velocity is quarter-cycle out of phase with position and is largest at equilibrium.
Volume flow rate
Q=Av measures volume passing a cross-section per time.
Weight
Weight is the gravitational force acting on an object; near Earth its magnitude is approximately mg.
Weight / gravitational force
Long-range force exerted by Earth on an object near Earth.
Weight near Earth
For small height changes near Earth, F_g ≈ mg is a useful local approximation.
Whole forces on an AP free-body diagram
Draw each external force as its own straight vector from the dot/center-of-mass representation; do not replace the force with x/y components on the FBD.
Work–energy theorem for rotation
Net rotational work equals change in rotational kinetic energy.
Zero net torque
Rotational equilibrium requires Στ=0 about the chosen axis.
Zero work
Work is zero when force is perpendicular to displacement or when displacement is zero.