AP Physics 1: Algebra-Based Vocabulary

Absolute Pressure

The total pressure at a point in a fluid, equal to the sum of atmospheric pressure and gauge pressure: P_abs = P_atm + ρgh.

Example: "The          at the bottom of the swimming pool includes both the atmospheric pressure and the pressure due to the water above."

Acceleration

The rate of change of velocity with respect to time; a vector quantity measured in m/s².

Example: "A car increasing its speed from rest experiences a positive          in the direction of motion."

Acceleration Due to Gravity

The acceleration experienced by an object in free fall near Earth's surface, approximately 9.8 m/s² directed downward.

Similar definitions: gravitational acceleration, g

Example: "When dropped from a tall building, the ball fell with an          of 9.8 m/s²."

Accuracy

How close a measured value is to the true or accepted value of the quantity being measured.

Example: "If the actual length is 2.00 m and a student measures 2.01 m, the measurement has high         ."

Action-Reaction Pair

Two forces described by Newton's third law that are equal in magnitude, opposite in direction, and act on different objects.

Example: "When you push on a wall, the wall pushes back on you — these two forces form an         ."

Air Resistance

A force opposing the motion of an object through air, dependent on the object's speed, shape, and surface area.

Similar definitions: drag force, aerodynamic drag

Example: "A skydiver reaches terminal velocity when          equals the force of gravity."

Amplitude

The maximum displacement of an oscillating object from its equilibrium position.

Example: "The          of the pendulum's swing decreased over time due to damping."

Angular Acceleration

The rate of change of angular velocity with respect to time, measured in rad/s².

Similar definitions: rotational acceleration

Example: "When the spinning wheel slowed down, it experienced a negative         ."

Angular Displacement

The angle through which an object rotates about a fixed axis, measured in radians.

Example: "After two full rotations, the wheel had an          of 4π radians."

Angular Frequency

The rate of oscillation measured in radians per second; ω = 2πf = 2π/T. Used in SHM and circular motion.

Example: "The          of the spring-mass system determines how rapidly it oscillates back and forth."

Angular Impulse

The product of torque and the time interval over which it acts, equal to the change in angular momentum.

Example: "The          delivered by the brake pad brought the rotating disc to a stop."

Angular Momentum

The rotational analog of linear momentum, defined as L = Iω for rigid bodies; a conserved quantity when no net external torque acts.

Example: "An ice skater pulling in her arms reduces her moment of inertia and increases her angular velocity, conserving         ."

Angular Position

The angle of an object relative to a reference line, measured in radians; the rotational analog of position.

Example: "The          of the minute hand on a clock changes by 2π radians every hour."

Angular Velocity

The rate of change of angular displacement with respect to time, measured in rad/s.

Similar definitions: rotational velocity

Example: "The          of the merry-go-round increased as more force was applied."

Apparent Weight

The normal force experienced by an object, which can differ from true weight when the object is accelerating (e.g., in an elevator).

Example: "When the elevator accelerates upward, your          increases because the floor must push harder to accelerate you."

Applied Force

A force that is applied to an object by a person or another object through direct contact.

Example: "The worker pushed the crate across the floor by exerting an          of 50 N."

Archimedes' Principle

The buoyant force on an object submerged in a fluid equals the weight of the fluid displaced by that object.

Example: "Using         , we can determine that a block of wood floats because it displaces a weight of water equal to its own weight."

Area Under the Curve

On a physics graph, the area between the plotted line and the horizontal axis represents a physical quantity (e.g., area under a v-t graph gives displacement; area under an F-t graph gives impulse).

Example: "The          of a velocity-time graph equals the object's displacement during that interval."

Atwood Machine

A device consisting of two masses connected by a string over a pulley, used to study Newton's second law and acceleration due to unbalanced forces.

Example: "In the         , the heavier mass accelerates downward while the lighter mass accelerates upward."

Average Acceleration

The change in velocity divided by the elapsed time interval: a_avg = Δv/Δt.

Example: "The          of the sprinter was calculated by dividing the change in speed by the time taken."

Average Speed

The total distance traveled divided by the total time elapsed; a scalar quantity.

Example: "Even though the runner slowed down during the race, her          was 8 m/s over the entire distance."

Average Velocity

The total displacement divided by the total time elapsed: v_avg = Δx/Δt; a vector quantity.

Example: "Although the car sped up and slowed down, its          over the entire trip was 50 km/h north."

Axis of Rotation

The fixed or instantaneous line about which an object rotates; torque and moment of inertia are defined relative to this line.

Example: "A door's hinges define the          around which the door swings open and closed."

Balanced Forces

Forces acting on an object that are equal in magnitude and opposite in direction, resulting in a net force of zero and no change in motion.

Example: "A book resting on a table has          because gravity pulling it down is matched by the normal force pushing it up."

Banked Curve

A curved road or track tilted at an angle so that a component of the normal force provides centripetal force, reducing or eliminating the need for friction.

Example: "A          allows cars to take a turn at higher speeds because the tilt of the road helps supply the centripetal force."

Bernoulli's Equation

A statement of energy conservation for flowing fluids that relates pressure, velocity, and height: P + ½ρv² + ρgh = constant.

Similar definitions: Bernoulli's principle

Example: "Using         , we can explain why airplane wings generate lift as air moves faster over the top surface."

Buoyancy

The tendency of a fluid to exert an upward force on an object placed in it, allowing objects less dense than the fluid to float.

Example: "A ship floats because of          — the water pushes up on the hull with a force equal to the weight of the displaced water."

Buoyant Force

The upward force exerted by a fluid on an immersed object, equal in magnitude to the weight of the displaced fluid.

Example: "The          acting on the submerged ball was large enough to push it back to the surface."

Center of Mass

The point at which a system's entire mass can be considered concentrated; it moves as though all external forces act on it.

Example: "The          of the two-object system followed a parabolic trajectory even as the objects spun around each other."

Center of Mass Velocity

The velocity of the center of mass of a system, found by dividing the total momentum by the total mass: v_cm = p_total / m_total.

Example: "In an explosion, the          of the fragments remains the same as the velocity of the original object before the explosion."

Centripetal Acceleration

The acceleration directed toward the center of a circular path, with magnitude a_c = v²/r.

Example: "As the car rounded the curve, the          kept it on the circular path."

Centripetal Force

The net inward force that causes an object to follow a curved or circular path, directed toward the center of curvature.

Example: "Tension in the string provides the          needed to keep the ball moving in a circle."

Closed System

A system that exchanges no matter with its surroundings. When no net external force acts, momentum is conserved; when no net external torque acts, angular momentum is conserved.

Similar definitions: isolated system

Example: "In a         , the total momentum before and after a collision remains the same."

Coefficient of Kinetic Friction

The ratio of the kinetic friction force to the normal force for two surfaces in relative motion; denoted μ_k.

Example: "The          between the box and the floor determined how much force was needed to keep it sliding."

Coefficient of Static Friction

The ratio of the maximum static friction force to the normal force for two surfaces not in relative motion; denoted μ_s. Always greater than or equal to μ_k for the same surfaces.

Example: "The          between rubber tires and dry pavement is high, preventing the car from slipping."

Collision

An interaction between two or more objects in which they exert forces on each other over a short time interval, often resulting in changes in velocity.

Example: "During the         , the two carts exchanged momentum, and the total momentum of the system was conserved."

Component

The projection of a vector along a coordinate axis; any vector can be broken into perpendicular components (e.g., F_x = F cos θ, F_y = F sin θ).

Example: "The horizontal          of the velocity determines how far the projectile travels sideways."

Compression (Spring)

A force or deformation that squeezes or shortens an object, such as a spring pushed together from its natural length.

Example: "When you push both ends of a spring together, the spring is under         ."

Conservation of Angular Momentum

The total angular momentum of a system remains constant when no net external torque acts on it.

Example: "The          explains why a spinning figure skater speeds up when pulling her arms inward."

Conservation of Energy

The total energy of an isolated system remains constant; energy can be transformed from one form to another but cannot be created or destroyed.

Example: "Using the principle of         , we can equate the potential energy at the top of a hill to the kinetic energy at the bottom."

Conservation of Linear Momentum

The total linear momentum of a closed system remains constant when no net external force acts on it.

Similar definitions: conservation of momentum

Example: "The          allows us to predict the velocities of two objects after they collide."

Conservative Force

A force for which the work done is independent of the path taken and depends only on the initial and final positions; examples include gravity and spring forces.

Example: "Gravity is a          because the work it does on a falling object depends only on the change in height."

Constant Acceleration

Motion in which the acceleration does not change over time, allowing the use of kinematic equations.

Similar definitions: uniform acceleration

Example: "Free fall near Earth's surface is an example of          at 9.8 m/s² downward."

Constant Velocity

Motion in which both speed and direction remain unchanged over time, meaning acceleration is zero.

Similar definitions: uniform velocity

Example: "A car cruising on a straight highway at 60 km/h is traveling at         ."

Contact Force

A force that requires physical contact between two objects to act, such as friction, tension, or the normal force.

Example: "When you push a box across the floor, your hand exerts a          on it."

Continuity Equation

A principle stating that for an incompressible fluid flowing through a pipe, the product of cross-sectional area and velocity remains constant: A₁v₁ = A₂v₂.

Example: "The          explains why water flows faster through a narrower section of a garden hose."

Controlled Experiment

An experiment in which one variable is changed at a time while all others are held constant, allowing a cause-and-effect relationship to be determined.

Example: "In a         , we changed only the mass on the spring while keeping the spring constant the same to study the effect on period."

Conversion Factor

A ratio used to convert a measurement from one unit to another without changing the quantity's value (e.g., 1 km = 1000 m).

Similar definitions: unit conversion

Example: "To convert 5 km to meters, multiply by the          of 1000 m per km."

Cross-Sectional Area

The area of a two-dimensional slice through an object or pipe, perpendicular to a specified direction; important in fluid dynamics and pressure calculations.

Example: "In the continuity equation, the          of the pipe and the fluid velocity are inversely related."

Damped Oscillation

Oscillatory motion in which the amplitude decreases over time due to energy loss from non-conservative forces like friction or air resistance.

Similar definitions: damped harmonic motion

Example: "A pendulum swinging in air undergoes          because friction and air resistance gradually reduce its amplitude."

Damping

The gradual loss of energy in an oscillating system due to non-conservative forces such as friction or air resistance.

Example: "The          of the swinging pendulum caused its amplitude to decrease with each cycle."

Deceleration

A decrease in the speed of an object; occurs when acceleration is opposite to the direction of velocity. Not a separate type of acceleration — it is simply negative acceleration relative to the direction of motion.

Example: "The car experienced          when the driver applied the brakes, slowing from 30 m/s to rest."

Density

The mass per unit volume of a substance, measured in kg/m³; ρ = m/V.

Example: "Objects with a          less than that of water will float on the surface."

Dependent Variable

The variable in an experiment that is measured and expected to change in response to changes in the independent variable.

Example: "In studying how force affects acceleration, acceleration is the          because it changes when force is varied."

Dimensional Analysis

A technique for checking the validity of an equation or converting units by analyzing the dimensions (such as length, mass, and time) on both sides.

Example: "Using         , we can verify that kinetic energy (½mv²) has units of kg·m²/s², which is equivalent to joules."

Direction

The orientation of a vector quantity in space, typically described using angles, compass bearings, or positive/negative signs along an axis.

Example: "Velocity includes both speed and         , such as 25 m/s to the east."

Displacement

The change in position of an object; a vector quantity with both magnitude and direction, measured in meters.

Example: "A runner who completes one lap around a circular track has a          of zero."

Displacement-Time Graph

A graph plotting an object's position (displacement) on the vertical axis versus time on the horizontal axis. The slope at any point gives the instantaneous velocity.

Similar definitions: position-time graph, x-t graph

Example: "A straight line with positive slope on a          indicates motion at constant positive velocity."

Dissipated Energy

Energy that is converted from mechanical energy into thermal energy (heat), sound, or other non-recoverable forms due to non-conservative forces.

Example: "When brakes are applied, kinetic energy is transformed into          as friction heats the brake pads."

Distance

The total length of the path traveled by an object, regardless of direction; a scalar quantity.

Example: "Even though the hiker returned to the starting point, the total          covered was 10 km."

Dynamic Equilibrium

A state in which an object moves at constant velocity because the net force acting on it is zero.

Example: "A skydiver falling at terminal velocity is in          because the drag force equals the gravitational force."

Dynamics

The branch of mechanics that studies the causes of motion, focusing on forces and torques and how they produce acceleration.

Example: "While kinematics describes how objects move,          explains why they move by analyzing the forces involved."

Efficiency

The ratio of useful work output to total energy input, often expressed as a percentage: efficiency = (W_out / E_in) × 100%.

Example: "The          of the motor was only 60%, meaning 40% of the input energy was lost as heat."

Elastic Collision

A collision in which both momentum and kinetic energy are conserved; the objects bounce off each other with no energy lost to deformation or heat.

Example: "Two billiard balls striking each other approximate an          because very little kinetic energy is lost."

Elastic Potential Energy

The energy stored in an elastic object, such as a spring, when it is stretched or compressed; given by PE = ½kx².

Similar definitions: spring potential energy

Example: "A compressed spring stores          that is released when the spring returns to its natural length."

Energy

The ability to do work or cause change; a scalar quantity measured in joules (J) that can exist in many forms including kinetic, potential, and thermal.

Example: "A moving car has kinetic         , and a stretched spring has elastic potential         ."

Energy Bar Chart

A visual representation showing the amounts of different types of energy (kinetic, gravitational PE, elastic PE, thermal) in a system at different points in a process, used to track energy transformations.

Example: "An          for a ball dropped from a height would show gravitational PE decreasing and kinetic energy increasing."

Energy Conservation (Mechanical)

In the absence of non-conservative forces, the total mechanical energy (KE + PE) of a system remains constant: KE_i + PE_i = KE_f + PE_f.

Example: "Using         , we can find the speed of a roller coaster at the bottom of a hill from its height at the top."

Energy Transformation

The process of energy changing from one form to another, such as potential energy converting to kinetic energy or mechanical energy converting to thermal energy.

Example: "As a ball falls, an          occurs: gravitational potential energy converts into kinetic energy."

Equilibrium

A state in which the net force and net torque on an object are both zero, so the object has no translational or rotational acceleration.

Example: "A balanced seesaw with equal weights on both sides is in         ."

Equilibrium Position

The position at which the net force on an oscillating object is zero; the point about which it oscillates in simple harmonic motion.

Similar definitions: rest position

Example: "A mass on a spring oscillates back and forth through its          where the spring is neither stretched nor compressed."

Explosion

An event in which a single object or system breaks apart into multiple pieces; internal forces do the work, and total momentum is conserved if the system is isolated.

Example: "When a firecracker at rest explodes into two pieces, the pieces fly off in opposite directions, but total momentum remains zero — this is analyzed as an         ."

External Force

A force applied to a system from outside its boundaries that can change the system's total momentum or mechanical energy.

Example: "Friction from the road is an          acting on the car system, slowing it down."

Float

The condition of an object resting at the surface of a fluid, occurring when the buoyant force equals the object's weight; requires the object's average density to be less than or equal to the fluid's density.

Example: "A block of wood will          on water because its density is less than that of water."

Flow Rate

The volume of fluid passing through a given cross-section per unit time; Q = Av.

Similar definitions: volume flow rate

Example: "The          through the pipe increased when the valve was opened wider."

Fluid

A substance that can flow and takes the shape of its container; both liquids and gases are classified as fluids.

Example: "Water and air are both examples of a          because they flow and conform to the shape of their containers."

Fluid Dynamics

The study of fluids in motion, including concepts such as flow rate, the continuity equation, and Bernoulli's equation.

Example: "         helps engineers design pipes and airplane wings by analyzing how fluids behave when they move."

Fluid Statics

The study of fluids at rest, including concepts such as pressure variation with depth, Pascal's principle, and buoyancy.

Similar definitions: hydrostatics

Example: "         explains why the pressure at the bottom of a swimming pool is greater than at the surface."

Force

A push or pull on an object that can cause it to accelerate, decelerate, or change direction; measured in newtons (N). A vector quantity.

Example: "A          of 10 N was applied to the box, causing it to slide across the floor."

Force of Gravity

The attractive force between any two objects with mass; near Earth's surface, F_g = mg directed downward.

Similar definitions: gravitational force, weight

Example: "The          on a 2 kg object near Earth's surface is approximately 19.6 N downward."

Force Pair

The two equal-and-opposite forces described by Newton's third law; they always act on two different objects simultaneously.

Similar definitions: action-reaction pair, Newton's third law pair

Example: "When a hammer hits a nail, the hammer exerts a force on the nail and the nail exerts an equal force back on the hammer — they are a         ."

Free Body Diagram

A visual representation showing all the forces acting on a single object, drawn as arrows indicating magnitude and direction.

Similar definitions: force diagram, FBD

Example: "Drawing a          helps identify all the forces on an object so you can apply Newton's second law."

Free Fall

Motion of an object under the influence of gravity alone, with no air resistance, where the only acceleration is g ≈ 9.8 m/s² downward.

Example: "An astronaut training in a special aircraft experiences          for short periods when the plane follows a parabolic trajectory."

Frequency

The number of complete oscillations or cycles per unit time, measured in hertz (Hz); f = 1/T.

Example: "A mass on a spring completing 5 oscillations per second has a          of 5 Hz."

Friction

A contact force that opposes the relative motion or tendency of motion between two surfaces; can be static or kinetic.

Example: "Without         , it would be impossible to walk because your feet would slip on the ground."

Fulcrum

The pivot point about which a lever rotates; the location of the axis of rotation for a lever.

Example: "A seesaw balances when the torques on either side of the          are equal."

Gauge Pressure

The pressure measured relative to atmospheric pressure; the difference between absolute pressure and atmospheric pressure: P_gauge = P_abs − P_atm.

Example: "A tire pressure reading of 32 psi is a          measurement, not including atmospheric pressure."

Gravitational Constant

The proportionality constant G = 6.674 × 10⁻¹¹ N·m²/kg² in Newton's law of universal gravitation.

Example: "The          is extremely small, which is why gravitational forces between everyday objects are negligible."

Gravitational Field

The region of space around a massive object in which another mass experiences a gravitational force; field strength is g = F/m, measured in N/kg or m/s².

Example: "Earth's          strength decreases with increasing altitude above the surface."

Gravitational Field Strength

The force per unit mass experienced by an object in a gravitational field; g = GM/r² at a distance r from the center of a mass M. Near Earth's surface, g ≈ 9.8 N/kg.

Example: "The          on the surface of Mars is about 3.7 N/kg, which is less than on Earth."

Gravitational Force

The attractive force between any two objects with mass, described by Newton's law of universal gravitation: F = Gm₁m₂/r².

Similar definitions: gravity

Example: "The          between Earth and the Moon keeps the Moon in orbit."

Gravitational Potential Energy

The energy stored in an object due to its position in a gravitational field; near Earth's surface, PE = mgh.

Example: "A book on a high shelf has more          than the same book on the floor."

Hertz

The SI unit of frequency, equal to one cycle per second: 1 Hz = 1 s⁻¹.

Example: "A pendulum completing two full swings per second has a frequency of 2         ."

Hooke's Law

The restoring force of a spring is proportional to the displacement from equilibrium and acts in the opposite direction: F = −kx.

Example: "         predicts that doubling the stretch of a spring doubles the restoring force."

Horizontal Projectile

A projectile launched with an initial velocity that is entirely horizontal, so its initial vertical velocity is zero.

Example: "A ball rolling off the edge of a table becomes a          and follows a parabolic path to the ground."

Hydraulic Press

A device that uses an enclosed fluid to multiply force; based on Pascal's principle, a small force on a small piston creates a large force on a large piston.

Similar definitions: hydraulic lift, hydraulic jack

Example: "A          allows a mechanic to lift a heavy car by applying a small force to a small piston."

Hydrostatic Pressure

The pressure exerted by a fluid at rest due to the weight of the fluid above a given point: P = ρgh.

Example: "         increases with depth, which is why a diver feels more pressure the deeper they go."

Ideal Fluid

A theoretical fluid that is incompressible, has no viscosity, and flows without energy loss due to internal friction.

Example: "Bernoulli's equation applies exactly only to an         , but it provides a good approximation for many real fluids."

Impulse

The product of the net force acting on an object and the time interval over which it acts; equal to the change in momentum: J = FΔt = Δp.

Example: "An airbag increases the time of impact, reducing the average force while delivering the same          to the passenger."

Impulse-Momentum Theorem

The net impulse on an object equals its change in momentum: J = FΔt = Δp = mΔv.

Example: "The          explains why catching a ball with soft hands (longer time) reduces the impact force."