Glossary of Terms
This glossary contains ISO 11179-compliant definitions for all physics concepts covered in this course. Definitions are designed to be precise, concise, distinct, non-circular, and appropriate for high school students with Algebra II and Geometry prerequisites.
Acceleration
The rate of change of velocity with respect to time, measured in meters per second squared (m/s²).
Example: A car accelerates from rest to 60 mph in 5 seconds, experiencing a constant acceleration throughout this period.
Acceleration-Time Graphs
Graphical representations showing how acceleration varies over time, with time on the horizontal axis and acceleration on the vertical axis.
Example: An acceleration-time graph for a rocket launch shows a spike during engine ignition, then drops to zero during coasting.
Acoustic Resonance
The phenomenon where a sound-producing system vibrates with maximum amplitude at specific frequencies corresponding to its natural modes.
Example: When you blow across a bottle opening, it produces a specific tone because the air column resonates at its natural frequency.
Action-Reaction Pairs
Two forces that are equal in magnitude, opposite in direction, and act on different objects as described by Newton's Third Law.
Example: When you push against a wall, the wall pushes back on you with an equal force in the opposite direction.
Amplitude
The maximum displacement of a wave or oscillating object from its equilibrium position.
Example: A pendulum swinging 10 centimeters to each side of center has an amplitude of 10 centimeters.
Angled Projection
Projectile motion where an object is launched at an angle to the horizontal, resulting in both horizontal and vertical velocity components.
Example: A soccer ball kicked at a 45-degree angle follows a parabolic path before landing downfield.
Angular Acceleration
The rate of change of angular velocity with respect to time, typically measured in radians per second squared (rad/s²).
Example: A spinning figure skater pulling in their arms experiences angular acceleration as their rotation rate increases.
Angular Displacement
The angle through which an object rotates about a fixed axis, measured in radians or degrees.
Example: A wheel completing one full rotation undergoes an angular displacement of 2π radians or 360 degrees.
Angular Frequency
The rate of change of the phase of a sinusoidal waveform, equal to 2π times the frequency, measured in radians per second.
Example: A mass oscillating on a spring with a frequency of 2 Hz has an angular frequency of 4π rad/s.
Angular Momentum
The rotational analog of linear momentum, calculated as the product of rotational inertia and angular velocity.
Example: A spinning ice skater has angular momentum that remains constant when no external torques act on them.
Angular Velocity
The rate of change of angular displacement with respect to time, typically measured in radians per second (rad/s).
Example: A merry-go-round completing one rotation every 10 seconds has an angular velocity of π/5 rad/s.
Atwood Machine
A simple mechanical system consisting of two masses connected by a string passing over a pulley, used to study Newton's laws.
Example: In a physics lab, students use an Atwood machine to measure gravitational acceleration by analyzing the motion of unequal masses.
Banked Curves
Curved roadways or tracks tilted at an angle to the horizontal, allowing vehicles to navigate turns at higher speeds safely.
Example: NASCAR race tracks have steeply banked curves that enable cars to maintain high speeds through turns without excessive friction.
Beats
A periodic variation in sound intensity produced when two waves of slightly different frequencies interfere.
Example: When tuning a guitar, you hear beats between the string being tuned and a reference pitch until they match.
Center of Mass
The point where an object's mass can be considered concentrated for analysis of translational motion.
Example: A properly balanced mobile hangs horizontally because it's suspended at its center of mass.
Centripetal Acceleration
The acceleration directed toward the center of a circular path that changes the direction of an object's velocity without changing its speed.
Example: The moon experiences centripetal acceleration toward Earth as it orbits, keeping it in its circular path.
Centripetal Force
The net force directed toward the center of a circular path that causes an object to follow that curved trajectory.
Example: When you swing a ball on a string in a circle, the tension in the string provides the centripetal force.
Charging by Contact
The transfer of electric charge between objects when they physically touch, resulting in both objects having the same type of charge.
Example: A charged metal rod touching a neutral metal sphere transfers some charge to the sphere.
Charging by Friction
The generation of electric charge through rubbing two different materials together, causing electrons to transfer from one to the other.
Example: Rubbing a balloon on your hair transfers electrons, allowing the balloon to stick to a wall.
Charging by Induction
The redistribution of charge in an object caused by the presence of a nearby charged object without direct contact.
Example: A charged rod brought near a neutral electroscope causes the leaves to separate temporarily without touching.
Coefficient of Friction
A dimensionless value representing the ratio of friction force to normal force between two surfaces.
Example: Ice on steel has a coefficient of friction around 0.02, explaining why ice skating is so smooth.
Color Addition
The process of combining colored light beams to produce new colors, where red, green, and blue are primary additive colors.
Example: Stage lighting uses red, green, and blue lights that can combine to create white light or any color.
Color Subtraction
The process of removing specific wavelengths from white light through absorption by pigments or filters.
Example: A cyan filter absorbs red light and transmits blue and green, demonstrating subtractive color mixing.
Concave Lenses
Lenses that are thinner in the center than at the edges, causing parallel light rays to diverge.
Example: Eyeglasses for nearsightedness use concave lenses to help focus distant objects correctly on the retina.
Concave Mirrors
Curved mirrors with a reflecting surface that curves inward, capable of focusing light and producing magnified images.
Example: A makeup mirror is concave, producing an enlarged, upright image of your face when held close.
Conductors
Materials that allow electric charge to flow freely due to loosely bound electrons.
Example: Copper wires are excellent conductors, making them ideal for electrical circuits.
Conservation of Angular Momentum
The principle stating that angular momentum remains constant in a closed system when no external torque acts.
Example: A figure skater spins faster when pulling in their arms because angular momentum is conserved.
Conservation of Charge
The fundamental principle that the total electric charge in an isolated system remains constant over time.
Example: When you rub a balloon on your hair, the negative charge gained by the balloon equals the positive charge left on your hair.
Conservation of Energy
The principle stating that the total energy in an isolated system remains constant, though it may transform between different forms.
Example: A roller coaster converts gravitational potential energy to kinetic energy and back as it moves through the track.
Conservation of Momentum
The principle stating that the total momentum of an isolated system remains constant when no external forces act.
Example: In a collision between billiard balls, the total momentum before impact equals the total momentum after.
Conservative Forces
Forces for which the work done in moving an object between two points is independent of the path taken.
Example: Gravity is a conservative force—lifting a book to a shelf requires the same work regardless of the path.
Constructive Interference
The combination of two or more waves where their amplitudes add together, producing a wave with greater amplitude.
Example: When two water wave crests meet, they combine through constructive interference to create a higher crest.
Convex Lenses
Lenses that are thicker in the center than at the edges, causing parallel light rays to converge at a focal point.
Example: A magnifying glass is a convex lens that focuses sunlight to a point hot enough to start a fire.
Convex Mirrors
Curved mirrors with a reflecting surface that bulges outward, producing reduced, upright virtual images.
Example: Store security mirrors are convex, providing a wide-angle view of the entire room.
Coulomb's Law
The mathematical relationship describing the electric force between two charged objects as directly proportional to the product of their charges and inversely proportional to the square of the distance between them.
Example: Doubling the distance between two charged particles reduces the electric force between them to one-fourth its original value.
Critical Angle
The angle of incidence in the denser medium above which total internal reflection occurs at the boundary with a less dense medium.
Example: Fiber optic cables use critical angles to keep light trapped inside by total internal reflection.
Cross Product
A vector operation that produces a third vector perpendicular to two input vectors, with magnitude equal to the product of their magnitudes and the sine of the angle between them.
Example: Torque is calculated as the cross product of the position vector and force vector.
Damped Harmonic Motion
Oscillatory motion in which the amplitude gradually decreases over time due to energy loss from resistive forces.
Example: A car's shock absorbers create damped harmonic motion, quickly reducing oscillations after hitting a bump.
Decibel Scale
A logarithmic scale used to measure sound intensity level, where each 10-decibel increase represents a tenfold increase in intensity.
Example: A whisper measures about 30 decibels, while a rock concert can reach 120 decibels.
Destructive Interference
The combination of two or more waves where their amplitudes subtract, producing a wave with reduced or zero amplitude.
Example: Noise-canceling headphones create sound waves opposite in phase to ambient noise, causing destructive interference that reduces unwanted sounds.
Diffraction Grating
An optical device with many closely spaced parallel slits that separates light into its component wavelengths through interference.
Example: A CD surface acts as a diffraction grating, producing rainbow patterns when white light reflects off it.
Dimensional Analysis
A mathematical technique using units of measurement to check equations and convert between different unit systems.
Example: Converting speed from miles per hour to meters per second requires dimensional analysis with conversion factors.
Dispersion
The separation of light into its component wavelengths due to the dependence of refractive index on wavelength.
Example: Sunlight passing through a prism separates into a rainbow due to dispersion.
Displacement
A vector quantity representing the straight-line distance and direction from an object's starting position to its ending position.
Example: Walking 3 blocks north, then 4 blocks east results in a displacement of 5 blocks northeast.
Distance
A scalar quantity measuring the total length of the path traveled by an object, regardless of direction.
Example: Running once around a 400-meter track covers a distance of 400 meters, even though your displacement is zero.
Dot Product
A vector operation that produces a scalar by multiplying the magnitudes of two vectors and the cosine of the angle between them.
Example: Work is calculated as the dot product of force and displacement vectors.
Doppler Effect
The change in observed frequency of a wave when there is relative motion between the source and the observer.
Example: A train whistle sounds higher pitched as it approaches and lower pitched as it moves away.
Dynamic Equilibrium
A state where an object moves with constant velocity because all forces acting on it are balanced.
Example: A parachutist falling at terminal velocity is in dynamic equilibrium with gravity and air resistance balanced.
Efficiency
The ratio of useful output energy to input energy, typically expressed as a percentage.
Example: An electric motor with 80% efficiency converts 80 joules of electrical energy into 64 joules of mechanical work.
Elastic Collisions
Collisions in which both momentum and kinetic energy are conserved.
Example: Billiard balls colliding on a pool table approximate elastic collisions, bouncing apart with minimal energy loss.
Elastic Potential Energy
Energy stored in a deformed elastic object, such as a compressed spring or stretched rubber band.
Example: A compressed spring stores elastic potential energy that can launch a toy car when released.
Electric Charge
A fundamental property of matter that causes it to experience electromagnetic force, existing in two types: positive and negative.
Example: Rubbing a balloon creates an excess of electrons, giving it a negative electric charge.
Electric Field
A region around a charged object where other charged objects experience an electric force.
Example: The space around a charged balloon creates an electric field that can attract small pieces of paper.
Electric Field Lines
Imaginary lines used to visualize electric fields, pointing in the direction of the force on a positive test charge.
Example: Electric field lines radiate outward from a positive charge and inward toward a negative charge.
Electric Force
The push or pull experienced by charged objects due to their electric charges.
Example: Two electrons repel each other with an electric force because both carry negative charge.
Electric Potential
The electric potential energy per unit charge at a point in an electric field, measured in volts.
Example: A 9-volt battery maintains a 9-joule energy difference per coulomb of charge between its terminals.
Electric Potential Energy
The energy stored in a system of charged objects due to their positions in an electric field.
Example: Separating opposite charges requires work, increasing their electric potential energy like lifting a mass increases gravitational potential energy.
Electromagnetic Spectrum
The complete range of electromagnetic waves organized by wavelength or frequency, from radio waves to gamma rays.
Example: The electromagnetic spectrum includes visible light (a tiny portion), radio waves, microwaves, infrared, ultraviolet, X-rays, and gamma rays.
Energy Diagrams
Graphical representations showing how potential energy and total energy vary with position for a system.
Example: An energy diagram for a pendulum shows potential energy highest at the ends of the swing and kinetic energy highest at the bottom.
Equilibrium
A state in which all forces acting on an object are balanced, resulting in zero net force.
Example: A book resting on a table is in equilibrium with gravity pulling down and the table pushing up with equal force.
Error Analysis
The systematic study of uncertainties in measurements and their propagation through calculations.
Example: When measuring a pendulum's period, error analysis accounts for reaction time uncertainty and calculates the resulting uncertainty in calculated gravity.
Field Strength
The magnitude of electric field at a point, equal to the force per unit charge, measured in newtons per coulomb.
Example: Near a Van de Graaff generator, field strength can be strong enough to make your hair stand on end.
Focal Length
The distance from a lens or mirror to its focal point where parallel rays converge or appear to diverge from.
Example: A magnifying glass with a 10-centimeter focal length focuses sunlight at a point 10 centimeters from the lens.
Force
A vector quantity representing a push or pull that can cause an object to accelerate, measured in newtons.
Example: Pushing a shopping cart with 50 newtons of force accelerates it forward.
Forced Oscillations
Oscillatory motion driven by an external periodic force rather than occurring naturally.
Example: Pushing a child on a swing at regular intervals creates forced oscillations.
Free Fall
Motion under the sole influence of gravity, where all objects accelerate downward at the same rate regardless of mass.
Example: A feather and hammer dropped on the Moon fall at the same rate because there's no air resistance.
Frequency
The number of complete oscillations or wave cycles occurring per unit time, measured in hertz (Hz).
Example: Middle C on a piano has a frequency of 261.6 Hz, meaning the string vibrates 261.6 times per second.
Friction
A force that opposes the relative motion or attempted motion between surfaces in contact.
Example: Friction between your shoes and the ground allows you to walk without slipping.
Graphical Analysis
The interpretation of physical relationships by examining graphs of related quantities.
Example: The slope of a position-time graph reveals an object's velocity.
Gravitational Potential Energy
Energy stored in an object due to its position in a gravitational field, calculated as mass times gravitational acceleration times height.
Example: A 10-kg boulder on a 5-meter cliff has 490 joules of gravitational potential energy.
Grounding
The process of connecting a charged object to Earth, allowing excess charge to flow away and neutralize the object.
Example: Lightning rods protect buildings by grounding them, providing a safe path for electric charge to reach Earth.
Harmonics
Standing wave patterns that occur at integer multiples of a system's fundamental frequency.
Example: A guitar string vibrates at its fundamental frequency and higher harmonics simultaneously, creating its distinctive tone.
Hooke's Law
The principle stating that the restoring force in a spring is directly proportional to its displacement from equilibrium.
Example: Stretching a spring 5 centimeters requires twice the force needed to stretch it 2.5 centimeters.
Horizontal Projection
Projectile motion where an object is launched horizontally, having initial horizontal velocity but zero initial vertical velocity.
Example: A marble rolled off a table edge has horizontal motion while simultaneously falling vertically.
Impulse
The product of force and the time interval over which it acts, equal to the change in momentum.
Example: An airbag increases collision time, reducing the force of impulse on passengers during a crash.
Impulse-Momentum Theorem
The principle stating that the impulse applied to an object equals its change in momentum.
Example: Catching a baseball with a glove demonstrates the impulse-momentum theorem as the glove increases stopping time to reduce impact force.
Inclined Plane
A flat surface tilted at an angle to the horizontal, used as a simple machine to raise objects with less force over a longer distance.
Example: A wheelchair ramp is an inclined plane that reduces the force needed to reach an elevated entrance.
Inclined Plane as Machine
An inclined plane analyzed as a simple machine that trades increased distance for decreased force.
Example: A loading ramp for trucks is 4 times as long as it is high, reducing required lifting force by a factor of 4.
Index of Refraction
A dimensionless number indicating how much light slows down and bends when entering a material from vacuum.
Example: Water has an index of refraction of 1.33, meaning light travels 1.33 times slower in water than in vacuum.
Inelastic Collisions
Collisions in which momentum is conserved but kinetic energy is not, with some energy converted to other forms.
Example: A car crash is an inelastic collision where kinetic energy transforms into sound, heat, and deformation.
Inertia
The tendency of an object to resist changes in its state of motion, proportional to its mass.
Example: A bowling ball has more inertia than a tennis ball, making it harder to start or stop moving.
Infrasound
Sound waves with frequencies below the range of human hearing, typically below 20 Hz.
Example: Elephants communicate using infrasound that can travel several kilometers.
Insulators
Materials that resist the flow of electric charge due to tightly bound electrons.
Example: Rubber coating on electrical wires acts as an insulator, preventing dangerous current flow.
Kinematic Equations
A set of four mathematical equations relating displacement, velocity, acceleration, and time for uniformly accelerated motion.
Example: Using kinematic equations, you can calculate how far a car travels while accelerating from rest to highway speed.
Kinetic Energy
Energy possessed by an object due to its motion, calculated as one-half mass times velocity squared.
Example: A 1000-kg car traveling at 20 m/s has 200,000 joules of kinetic energy.
Kinetic Friction
The friction force between surfaces in relative motion, typically less than static friction.
Example: Sliding a book across a table encounters kinetic friction that gradually slows it down.
Law of Reflection
The principle stating that the angle of incidence equals the angle of reflection when light bounces off a surface.
Example: When light hits a mirror at a 30-degree angle to the normal, it reflects at a 30-degree angle on the opposite side.
Lens Equation
A mathematical relationship connecting object distance, image distance, and focal length for lenses.
Example: Using the lens equation, you can calculate where a camera lens will focus light from a distant object.
Lenses
Transparent optical devices that refract light to form images by converging or diverging light rays.
Example: Eyeglasses use lenses to correct vision by properly focusing light onto the retina.
Lever
A rigid bar that rotates about a fixed pivot point (fulcrum), functioning as a simple machine to amplify force or distance.
Example: A crowbar is a lever that multiplies your input force to lift heavy objects.
Light Waves
Electromagnetic waves in the visible portion of the spectrum that can be detected by the human eye.
Example: Light waves from the sun travel through space to illuminate Earth.
Linear Momentum
The product of an object's mass and velocity, representing its quantity of motion.
Example: A 2-kg ball moving at 5 m/s has linear momentum of 10 kg·m/s.
Linear Motion
Motion along a straight line, described by position, velocity, and acceleration.
Example: A train traveling along a straight track exhibits linear motion.
Longitudinal Waves
Waves in which particle displacement is parallel to the direction of wave propagation.
Example: Sound waves are longitudinal, with air molecules vibrating back and forth in the same direction the sound travels.
Loudness
The subjective perception of sound intensity, influenced by both the amplitude of sound waves and the ear's sensitivity to different frequencies.
Example: A whisper has low loudness, while a jet engine has extremely high loudness.
Luminous Intensity
The amount of light energy emitted per unit time in a particular direction, measured in candelas.
Example: A typical candle has a luminous intensity of approximately one candela.
Magnification
The ratio of image size to object size produced by an optical system.
Example: A microscope with 400× magnification makes a cell appear 400 times larger than its actual size.
Mass vs Weight
The distinction between mass (the amount of matter in an object) and weight (the gravitational force acting on that mass).
Example: An astronaut's mass remains 70 kg on the Moon, but their weight is only about 115 newtons compared to 686 newtons on Earth.
Measurement
The process of quantitatively comparing a physical property to a standard unit.
Example: Using a ruler to determine that a pencil is 19 centimeters long is a measurement.
Mechanical Advantage
The ratio of output force to input force in a machine, indicating force multiplication.
Example: A pulley system with mechanical advantage of 4 allows you to lift 400 newtons using only 100 newtons of input force.
Mechanical Energy
The sum of kinetic energy and potential energy in a mechanical system.
Example: A swinging pendulum continuously exchanges mechanical energy between kinetic and potential forms.
Mechanical Waves
Waves that require a material medium to propagate, transferring energy through matter.
Example: Sound waves are mechanical waves that cannot travel through the vacuum of space.
Mirror Equation
A mathematical relationship connecting object distance, image distance, and focal length for mirrors.
Example: The mirror equation predicts where a concave mirror will form an image of your face.
Negative Charge
An excess of electrons relative to protons, conventionally represented as negative and repelling other negative charges.
Example: After rubbing a balloon on wool, the balloon gains a negative charge from extra electrons.
Net Force
The vector sum of all forces acting on an object, determining its acceleration according to Newton's Second Law.
Example: A 10-newton push to the right and a 3-newton push to the left result in a net force of 7 newtons to the right.
Newton's First Law
The principle stating that an object at rest stays at rest and an object in motion stays in motion with constant velocity unless acted upon by a net external force.
Example: A hockey puck sliding on ice continues moving in a straight line until friction or collision changes its motion.
Newton's Second Law
The principle stating that the net force on an object equals the product of its mass and acceleration (F = ma).
Example: Pushing a 5-kg cart with 20 newtons of net force produces an acceleration of 4 m/s².
Newton's Third Law
The principle stating that for every action force, there is an equal and opposite reaction force acting on a different object.
Example: When you jump, your legs push down on the ground, and the ground pushes up on you with equal force.
Nodes and Antinodes
Points in a standing wave where displacement is always zero (nodes) or maximum (antinodes).
Example: A vibrating guitar string has nodes at both ends where it's fixed and antinodes at points of maximum vibration.
Non-conservative Forces
Forces for which the work done depends on the path taken, typically converting mechanical energy to other forms.
Example: Friction is a non-conservative force that converts kinetic energy to thermal energy regardless of path.
Normal Force
The perpendicular contact force exerted by a surface on an object resting on it.
Example: A book on a table experiences an upward normal force from the table equal to the book's weight.
Optical Diffraction
The bending and spreading of light waves around obstacles or through openings.
Example: Light passing through a small slit creates a diffraction pattern with bright and dark bands on a screen.
Pendulum
A mass suspended from a fixed point that swings back and forth under the influence of gravity.
Example: A grandfather clock uses a pendulum to regulate its timekeeping through consistent oscillation periods.
Period
The time required for one complete oscillation or wave cycle, measured in seconds.
Example: A pendulum with a period of 2 seconds takes 2 seconds to swing forward and back to its starting position.
Perfectly Inelastic Collisions
Collisions where objects stick together after impact, resulting in maximum kinetic energy loss while conserving momentum.
Example: Two railroad cars coupling together during a collision is a perfectly inelastic collision.
Physical Pendulum
Any rigid body that oscillates about a fixed pivot point under gravitational torque.
Example: A baseball bat suspended from one end and allowed to swing acts as a physical pendulum.
Pitch
The subjective perception of sound frequency, with high frequencies perceived as high pitch and low frequencies as low pitch.
Example: A piccolo produces high-pitch sounds, while a tuba produces low-pitch sounds.
Plane Mirrors
Flat mirrors that produce virtual, upright images the same size as the object.
Example: A bathroom mirror is a plane mirror that shows your reflection at the same apparent distance behind the mirror as you are in front.
Polarization
The orientation of oscillations in a transverse wave, particularly the alignment of electric field oscillations in light.
Example: Polarized sunglasses block horizontally polarized light reflected from water, reducing glare.
Position-Time Graphs
Graphical representations showing how position varies over time, with time on the horizontal axis and position on the vertical axis.
Example: A position-time graph with a straight line indicates constant velocity motion.
Positive Charge
A deficit of electrons relative to protons, conventionally represented as positive and repelling other positive charges.
Example: A glass rod rubbed with silk acquires a positive charge by losing electrons.
Potential Energy
Stored energy in a system due to the position or configuration of objects.
Example: A compressed spring, an elevated mass, and separated opposite charges all have potential energy.
Power
The rate at which energy is transferred or work is performed, measured in watts (joules per second).
Example: A 100-watt light bulb converts 100 joules of electrical energy to light and heat every second.
Precision vs Accuracy
The distinction between the reproducibility of measurements (precision) and their closeness to the true value (accuracy).
Example: A poorly calibrated scale might give precise but inaccurate readings that cluster around the wrong value.
Prism
A transparent optical element with flat, polished surfaces that refract light, often used to disperse white light into colors.
Example: A triangular glass prism separates sunlight into a rainbow of colors.
Projectile Motion
Two-dimensional motion of an object under the influence of gravity alone, combining horizontal uniform motion with vertical accelerated motion.
Example: A basketball shot follows projectile motion, with a parabolic path determined by its initial velocity and gravity.
Proportional Reasoning
The mathematical skill of understanding and working with relationships where one quantity varies directly or inversely with another.
Example: Understanding that doubling the mass of an object doubles its weight demonstrates proportional reasoning.
Pulley as Machine
A pulley system analyzed as a simple machine that can change force direction and provide mechanical advantage.
Example: A crane uses multiple pulleys to lift heavy loads with less input force.
Pulley Systems
Arrangements of wheels and ropes that redirect forces and provide mechanical advantage for lifting loads.
Example: A flagpole uses a pulley system to raise and lower the flag easily.
Ray Diagrams
Schematic drawings using light rays to trace image formation by lenses and mirrors.
Example: A ray diagram for a convex lens shows how parallel rays converge at the focal point.
Real Images
Images formed where light rays actually converge, capable of being projected onto a screen.
Example: A movie projector creates a real image on the screen where light physically arrives.
Reflection
The bouncing of light or other waves off a surface, following the law of reflection.
Example: Seeing your image in a mirror is due to reflection of light from your face.
Refraction
The bending of waves as they pass from one medium to another due to a change in wave speed.
Example: A straw appears bent when placed in a glass of water due to refraction of light at the water-air boundary.
Relative Velocity
The velocity of one object as observed from the reference frame of another moving object.
Example: Two cars traveling 60 mph in the same direction have a relative velocity of zero, appearing stationary to each other.
Resonance
The dramatic increase in amplitude when a system is driven at its natural frequency.
Example: Pushing a child on a swing at the right timing creates resonance, building up a large amplitude with minimal effort.
Restoring Force
A force that acts to return a displaced object to its equilibrium position.
Example: When you stretch a spring, the restoring force pulls it back toward its natural length.
Rocket Propulsion
Locomotion achieved by expelling mass in one direction to generate thrust in the opposite direction, demonstrating Newton's Third Law.
Example: A rocket expels hot gas downward, and by Newton's Third Law, the gas pushes the rocket upward.
Rolling Motion
Combined rotational and translational motion where an object rolls without slipping along a surface.
Example: A bicycle wheel exhibits rolling motion, simultaneously rotating about its axis and translating forward.
Rotational Inertia
The resistance of a rotating object to changes in its rotational motion, depending on both mass and mass distribution.
Example: A figure skater has less rotational inertia with arms pulled in than with arms extended, explaining faster spinning.
Rotational Kinetic Energy
Energy associated with rotational motion, equal to one-half the rotational inertia times angular velocity squared.
Example: A spinning flywheel stores rotational kinetic energy that can be released to do work.
Rotational Kinematics
The description of rotational motion using angular displacement, angular velocity, and angular acceleration.
Example: Analyzing a spinning wheel's motion using rotational kinematics reveals how its angular velocity changes over time.
Scalars
Physical quantities that have magnitude but no direction.
Example: Temperature, mass, time, and speed are all scalars because they need only a number and unit to be specified.
Scientific Method
A systematic approach to investigating phenomena through observation, hypothesis formation, experimentation, and conclusion.
Example: Testing whether fertilizer affects plant growth involves the scientific method: forming a hypothesis, designing controlled experiments, and analyzing results.
Scientific Notation
A method of expressing very large or very small numbers as a product of a number between 1 and 10 and a power of 10.
Example: The speed of light, 300,000,000 m/s, is written as 3.0 × 10⁸ m/s in scientific notation.
Semiconductors
Materials with electrical conductivity between conductors and insulators, controllable by temperature or impurities.
Example: Silicon semiconductors in computer chips can be switched between conducting and insulating states to process information.
Shock Waves
Pressure waves formed when an object travels faster than the wave speed in that medium, creating a cone-shaped disturbance.
Example: A supersonic jet creates a shock wave heard on the ground as a sonic boom.
SI Units
The International System of Units, a standardized metric system using base units like meters, kilograms, and seconds.
Example: Scientists worldwide use SI units, measuring length in meters rather than feet or yards.
Significant Figures
The digits in a measurement that carry meaningful information about its precision.
Example: Measuring 12.50 cm has four significant figures, indicating precision to the hundredths place.
Simple Harmonic Motion
Oscillatory motion where the restoring force is directly proportional to displacement from equilibrium.
Example: A mass bobbing on a spring exhibits simple harmonic motion with sinusoidal position variation over time.
Simple Machines
Basic mechanical devices that change the magnitude or direction of forces, including levers, pulleys, inclined planes, wedges, screws, and wheels-and-axles.
Example: A screwdriver is a simple machine combining a wheel and axle to multiply torque.
Simple Pendulum
An idealized pendulum consisting of a point mass suspended by a massless string, swinging under gravity.
Example: A small dense bob on a long thin string approximates a simple pendulum for physics experiments.
Single Slit Diffraction
The spreading and interference pattern created when light passes through a single narrow opening.
Example: Laser light shining through a thin slit creates a single slit diffraction pattern with a bright central band and dimmer side bands.
Snell's Law
The mathematical relationship describing how light bends when crossing a boundary between materials with different refractive indices.
Example: Snell's Law explains why a pencil appears bent at the water surface in a glass.
Sound Intensity
The power per unit area carried by sound waves, measured in watts per square meter.
Example: Standing near a speaker produces higher sound intensity than standing far away, even though the power output is the same.
Sound Waves
Longitudinal mechanical waves that propagate through a medium as compressions and rarefactions.
Example: When you speak, sound waves travel through air to reach a listener's ear.
Speed
A scalar quantity measuring the rate of distance covered, calculated as distance divided by time.
Example: A car traveling 100 kilometers in 2 hours has a speed of 50 km/h.
Speed of Light
The constant speed at which electromagnetic radiation travels in vacuum, approximately 3.0 × 10⁸ meters per second.
Example: Light from the sun takes about 8 minutes to reach Earth, traveling at the speed of light through space.
Speed of Sound
The rate at which sound waves propagate through a medium, varying with the medium's properties and temperature.
Example: At room temperature, sound travels through air at approximately 343 meters per second.
Spherical Mirrors
Curved mirrors with surfaces that form part of a sphere, either concave or convex.
Example: Automobile side mirrors are spherical mirrors designed to provide a wide field of view.
Spring Constant
A measure of spring stiffness, equal to the force required per unit displacement, measured in newtons per meter.
Example: A spring with spring constant 100 N/m requires 50 newtons to stretch it 0.5 meters.
Standing Waves
Wave patterns that appear stationary, formed by interference between waves traveling in opposite directions.
Example: A guitar string vibrates in standing wave patterns with nodes at both ends.
Static Equilibrium
A state where an object remains at rest because all forces and torques acting on it are balanced.
Example: A ladder leaning against a wall is in static equilibrium when properly positioned.
Static Friction
The friction force between surfaces at rest relative to each other, preventing motion up to a maximum value.
Example: Static friction keeps a parked car stationary on a hill until the slope becomes too steep.
Superconductors
Materials that exhibit zero electrical resistance when cooled below a critical temperature.
Example: Superconducting magnets in MRI machines conduct electricity without energy loss, creating powerful magnetic fields.
Superposition Principle
The principle stating that when two or more waves overlap, the resultant displacement is the sum of individual displacements.
Example: When two water waves meet, they combine according to the superposition principle, creating regions of larger and smaller amplitude.
Tension
The pulling force transmitted through a string, rope, cable, or similar object when forces are applied at both ends.
Example: The tension in a rope during a tug-of-war equals the pulling force applied at each end.
Thin Lens Formula
An equation relating object distance, image distance, and focal length for thin lenses: 1/f = 1/do + 1/di.
Example: The thin lens formula calculates that an object 30 cm from a lens with 10 cm focal length creates an image 15 cm from the lens.
Total Internal Reflection
The complete reflection of light at the boundary between a denser and less dense medium when the angle of incidence exceeds the critical angle.
Example: Diamonds sparkle brilliantly because their high refractive index causes total internal reflection, trapping and reflecting light internally.
Torque
The rotational analog of force, equal to the product of force and perpendicular distance from the rotation axis.
Example: Using a longer wrench increases the distance from the bolt, multiplying the torque you can apply.
Transverse Waves
Waves in which particle displacement is perpendicular to the direction of wave propagation.
Example: Light waves and waves on a rope are transverse, with oscillations perpendicular to the wave's travel direction.
Trigonometry for Physics
The application of sine, cosine, and tangent functions to resolve vectors and analyze angular relationships in physical problems.
Example: Calculating the vertical component of a force applied at 30 degrees requires using sine or cosine from trigonometry.
2D Collisions
Collisions occurring in a plane where momentum must be conserved in both x and y directions independently.
Example: A billiard ball hitting another at an angle demonstrates a 2D collision with momentum vectors changing in two dimensions.
Ultrasound
Sound waves with frequencies above the range of human hearing, typically above 20,000 Hz.
Example: Medical ultrasound imaging uses high-frequency sound waves to visualize internal body structures.
Uniform Motion
Motion at constant velocity with zero acceleration.
Example: A car using cruise control on a straight highway maintains uniform motion.
Uniformly Accelerated Motion
Motion with constant acceleration, where velocity changes by equal amounts in equal time intervals.
Example: A ball dropped from rest undergoes uniformly accelerated motion with acceleration equal to g.
Unit Conversion
The process of changing a measurement from one unit system to another using conversion factors.
Example: Converting 50 miles per hour to meters per second requires unit conversion: 50 mi/h = 22.4 m/s.
Vector Addition
The process of combining two or more vectors to find their resultant using geometric or component methods.
Example: Walking 3 meters east then 4 meters north combines through vector addition to give a 5-meter northeast displacement.
Vector Components
The projections of a vector along coordinate axes, allowing two-dimensional vectors to be expressed as separate perpendicular parts.
Example: A force of 10 newtons at 30° above horizontal has components of 8.66 N horizontal and 5 N vertical.
Vector Subtraction
The process of finding the difference between vectors by adding the negative of the second vector to the first.
Example: Finding relative velocity requires vector subtraction of one object's velocity from another's.
Vectors
Physical quantities that have both magnitude and direction, represented by arrows in diagrams.
Example: Displacement, velocity, acceleration, and force are all vectors requiring both magnitude and direction for complete specification.
Velocity
A vector quantity describing the rate of change of position, including both speed and direction.
Example: A car traveling 60 km/h northward has a velocity that specifies both how fast and which direction it's moving.
Velocity-Time Graphs
Graphical representations showing how velocity varies over time, with time on the horizontal axis and velocity on the vertical axis.
Example: The area under a velocity-time graph represents the displacement traveled during that time interval.
Virtual Images
Images formed where light rays appear to diverge from, but do not actually pass through, unable to be projected onto a screen.
Example: The image you see in a plane mirror is a virtual image appearing behind the mirror surface.
Visible Spectrum
The portion of the electromagnetic spectrum detectable by human eyes, ranging from approximately 400 nm (violet) to 700 nm (red).
Example: A rainbow displays the visible spectrum as water droplets separate sunlight into its component wavelengths.
Voltage
The electric potential difference between two points, representing energy per unit charge, measured in volts.
Example: A 12-volt battery provides 12 joules of energy per coulomb of charge that flows through a circuit.
Wave Diffraction
The bending and spreading of waves as they pass through openings or around obstacles.
Example: You can hear someone talking around a corner because sound waves undergo diffraction, bending around the obstacle.
Wave Frequency
The number of wave cycles passing a fixed point per unit time, measured in hertz.
Example: FM radio waves with frequency 100 MHz have 100 million wave cycles passing by each second.
Wave Interference
The combination of two or more waves occupying the same space, producing a resultant wave.
Example: Ripples from two stones dropped in water demonstrate wave interference, creating complex patterns where they meet.
Wave Period
The time required for one complete wave cycle to pass a fixed point, equal to the reciprocal of frequency.
Example: Ocean waves with a 10-second period have a new crest arrive every 10 seconds.
Wave Properties
Characteristics that describe waves, including wavelength, frequency, amplitude, speed, and phase.
Example: Understanding wave properties allows us to distinguish between different types of electromagnetic radiation.
Wave Reflection
The bouncing back of waves when they encounter a boundary or obstacle.
Example: Echoes are caused by wave reflection of sound off distant surfaces like canyon walls.
Wave Refraction
The change in direction of waves as they pass from one medium to another at an angle, caused by a change in wave speed.
Example: Ocean waves bend as they approach shore due to wave refraction caused by decreasing water depth.
Wave Speed
The rate at which a wave disturbance propagates through a medium, equal to wavelength times frequency.
Example: Radio waves travel at the speed of light, approximately 300,000 kilometers per second through vacuum.
Wavelength
The spatial distance between two consecutive corresponding points on a wave, such as crest to crest or trough to trough.
Example: Red light has wavelengths around 700 nanometers, nearly twice the wavelength of violet light at 400 nanometers.
Weight
The gravitational force acting on an object, equal to mass times gravitational acceleration.
Example: A 10-kilogram object on Earth has a weight of approximately 98 newtons.
Work
The transfer of energy that occurs when a force acts on an object through a displacement in the direction of the force.
Example: Lifting a 20-kg box 1.5 meters requires 294 joules of work against gravity.
Work by Constant Force
Work calculated as the product of force magnitude, displacement magnitude, and the cosine of the angle between them.
Example: Pushing a lawn mower with 50 newtons of force over 20 meters requires 1000 joules of work.
Work by Variable Force
Work calculated by integrating force over displacement when the force magnitude changes during motion.
Example: Compressing a spring requires work by variable force because the spring force increases with compression.
Work-Energy Theorem
The principle stating that the net work done on an object equals its change in kinetic energy.
Example: The work-energy theorem explains that when you apply brakes, negative work reduces a car's kinetic energy to zero.
Young's Double Slit
An experiment demonstrating light's wave nature by passing light through two closely spaced slits, producing an interference pattern.
Example: Young's double slit experiment shows alternating bright and dark bands proving light behaves as a wave.