Physics Explorer
Search and explore 132 physics concepts
Explore 132 physics concepts organized across motion and change, forces and interaction, energy systems, waves, electricity, and magnetism. Each concept is explained in plain language with real-world intuition, common misconceptions to watch for, and connections to related ideas — so you can build a coherent understanding rather than memorizing isolated facts.
Electric Charge
Some particles carry an invisible 'label' — positive or negative — that makes them push or pull on each other.
Electric Current
Current is like the flow rate of water in a pipe — how much charge passes a point each second.
Voltage
Voltage is like water pressure — it's the 'push' that drives current through a circuit.
Resistance
Resistance is like friction for electricity — a narrow pipe resists water flow more than a wide one.
Ohm's Law
More push (voltage) means more flow (current). More resistance means less flow for the same push.
Circuit
A circuit is a complete loop — like a circular track that electrons run around. Break the loop and everything stops.
Series Circuit
Like cars on a single-lane road — every car (charge) must pass through every toll booth (component) in order.
Parallel Circuit
Like a river splitting into branches — the water (current) divides, but the pressure drop (voltage) across each branch is the same.
Circuit Diagram
A circuit diagram is like a map for electricity — it shows what's connected to what without drawing realistic pictures.
Kirchhoff's Laws
Charge cannot pile up at a junction, and energy per unit charge must balance around a complete loop.
Electrical Power
Power tells you how quickly a device uses energy — a 100 W bulb converts energy twice as fast as a 50 W bulb.
Force
Anything that makes something move, stop, speed up, slow down, or change direction.
Mass
How 'heavy' something feels when you try to push it, regardless of gravity.
Weight
How hard gravity pulls you toward the ground — it changes on different planets.
Newton's First Law
Things keep doing what they're doing unless something pushes or pulls them.
Newton's Second Law
Push harder and you get faster acceleration; heavier object means slower acceleration for the same push.
Newton's Third Law
When you push something, it pushes back on you just as hard.
Inertia
Heavy things are stubborn—hard to start moving, hard to stop.
Friction
The resistance you feel when sliding something across a rough surface — it always acts opposite to motion.
Normal Force
The floor pushing up on you so you don't fall through — it acts at a right angle to whatever surface the object touches.
Gravity
Everything pulls on everything else—but only huge things (like Earth) pull noticeably.
Net Force
What you get when you add up all pushes and pulls, accounting for direction.
Equilibrium
All forces cancel out — the object doesn't accelerate, though it may still be moving at constant velocity.
Tension
The 'tightness' you feel in a rope when both ends are being pulled in opposite directions.
Free Body Diagram
A simplified picture that shows every push and pull acting on one isolated object.
Momentum
How hard it is to stop something moving. Heavy and fast = lots of momentum.
Impulse
A big push for a short time or a small push for a long time can have the same effect.
Conservation of Momentum
Momentum can move between objects but can't be created or destroyed.
Centripetal Force
The force that pulls you toward the center when you go around a curve.
Torque
How hard you're twisting something. Depends on force AND distance from pivot.
Spring Force
Stretch a spring twice as far, it pulls back with exactly twice as much force.
Kinetic Friction
Once something is moving, friction resists its motion — less than static friction, but still present.
Static Friction
It takes more force to get something moving than to keep it moving.
Elastic Collision
Billiard balls bouncing off each other: the total energy stays the same, nothing is lost to heat or deformation.
Inelastic Collision
Two cars crashing and sticking together: they move as one object and kinetic energy is lost.
Angular Momentum
A spinning skater pulling their arms in spins faster — they're conserving angular momentum.
Statics
If something is not speeding up, slowing down, or rotating more, the pushes and twists must balance.
Pulley Systems
A pulley can make lifting easier by sharing the load between several rope segments.
Collisions
During a crash or bounce, forces act briefly but strongly, so motion can change a lot.
Rotational Equilibrium
If the clockwise and counterclockwise twists balance, the object will not start spinning faster one way or the other.
Waves
Energy traveling through something—like ripples on water. The water stays put; the ripple moves.
Wavelength
How 'long' one complete wave cycle is — the spatial size of a single repeating pattern.
Frequency
How many times something vibrates per second—high frequency means very rapid vibration.
Amplitude
How 'tall' the wave is measured from the center line — bigger amplitude carries more energy and produces stronger effects.
Wave Speed
How fast the wave's shape moves forward through whatever it's traveling in.
Transverse Wave
Shake a rope side-to-side: the wave travels along the rope, but the rope moves up and down.
Longitudinal Wave
A slinky pushed back and forth: compressions and stretches travel along it.
Sound
Vibrating air that your ears detect. No medium, no sound (space is silent).
Electromagnetic Waves
Light, radio, X-rays—all are EM waves, just different frequencies.
Electromagnetic Spectrum
A 'rainbow' that extends far beyond visible light in both directions.
Reflection
Like a ball bouncing off a wall—the wave reverses direction at the boundary.
Refraction
A straw looks bent in a glass of water because light bends at the surface.
Diffraction
Waves 'bend around corners'—you can hear someone even if you can't see them.
Interference
When waves meet, they add up or cancel out at each point depending on whether their crests and troughs align.
Doppler Effect
An ambulance siren sounds higher-pitched approaching, lower-pitched receding.
Period
How long it takes a swing to go all the way and come back to where it started.
Intensity
Intensity tells you how concentrated the wave's energy flow is.
Speed of Sound
Sound moves faster in some materials than in others because the medium's particles pass the disturbance along differently.
Pressure Wave
Instead of crests and troughs, the medium gets squeezed and spread out as the wave passes.
Pitch
Higher frequency sounds are heard as higher pitch.
Loudness
Bigger wave amplitude usually sounds louder.
Standing Waves
The pattern looks frozen, with points that never move and others that vibrate the most.
Harmonics
A string or air column can vibrate in several allowed patterns, each with its own frequency.
Resonance
Push at just the right rhythm and the vibration builds up much more than usual.
Energy
The 'currency' that makes things happen. It's what you need to move, heat, or change anything.
Work
Energy transferred by pushing something through space — force and displacement must both be present.
Kinetic Energy
The faster something moves and the heavier it is, the more kinetic energy it has.
Potential Energy
Energy waiting to be released—like a stretched rubber band or a ball held high.
Gravitational Potential Energy
The higher you lift something, the more energy it stores (ready to fall).
Elastic Potential Energy
A stretched rubber band 'wants' to snap back—that desire is stored energy.
Conservation of Energy
Energy is like money—you can spend it, save it, or change its form, but you can't make more out of nothing.
Work-Energy Theorem
The total work done on an object is exactly what changes its kinetic energy.
Power
How fast you use or produce energy. A powerful engine does work quickly.
Mechanical Energy
The combined 'useful' energy for mechanical motion — kinetic plus all forms of potential energy.
Thermal Energy
The energy of jiggling atoms and molecules—what we experience as temperature.
Heat Transfer
Heat always flows from hot to cold on its own — reversing this requires external work.
Temperature
How 'hot' or 'cold' something is—how fast its molecules are moving on average.
Efficiency
What fraction of the energy you put in actually goes where you want it to go, rather than being wasted as heat.
Simple Harmonic Motion
A spring or pendulum that bounces back and forth in a smooth, repeating pattern.
Conduction
Touch a hot pan — heat flows from the pan to your hand through direct contact.
Convection
Hot air rises and cool air sinks — this circulation carries heat through the room.
Radiation (Heat Transfer)
The sun warms you even through the vacuum of space — that's radiation.
Radioactive Decay
Some nuclei are unstable and naturally break down over time.
Nuclear Fission
A large unstable nucleus can split apart and release a huge amount of energy.
Nuclear Fusion
Small nuclei can combine and release energy, especially inside stars.
Photoelectric Effect
Light can hit a surface like tiny packets of energy and knock electrons out.
Special Relativity
At everyday speeds, classical physics works well. At speeds close to light, time and space behave differently from common intuition.
Electric Field
Every charge creates an invisible 'force zone' around it. Another charge entering this zone feels a push or pull without touching anything.
Coulomb's Law
Like gravity between masses, but for charges. Double the distance and the force drops to one quarter. Double either charge and the force doubles.
Electric Potential
Electric potential is like altitude on a hill — charges 'roll downhill' from high potential to low potential, just as balls roll from high ground to low ground.
Potential Difference
Potential difference is the 'height drop' that makes charges flow — the bigger the drop, the harder the push.
Magnetic Field
Moving charges create a swirling force field around them. This field can push on other moving charges or magnets.
Magnetic Force
A moving charge in a magnetic field feels a sideways push — perpendicular to both its motion and the field. It's like a cross-wind deflecting a moving ball.
Electromagnetic Induction
Push a magnet into a coil and current flows — the changing magnetic field 'induces' electricity. Pull it out and current flows the other way.
Faraday's Law
The faster you change the magnetic field through a loop, the bigger the voltage you get. Faraday's law tells you exactly how much.
Lenz's Law
Nature resists change — when you push a magnet into a coil, the coil creates its own magnetic field that pushes back.
Generator
Spin a loop of wire between magnets and you get electricity — the changing flux induces a voltage that drives current through an external circuit.
Transformer
A transformer trades voltage for current (or vice versa) — like a gear system trades speed for torque.
Electric Motor
Run current through a loop between magnets and it spins — the magnetic force on each side of the loop pushes in opposite directions, creating rotation.
Density
Density tells you how tightly matter is packed. Heavy for its size means high density.
Pressure
Pressure is how concentrated a force is. The same force on a smaller area creates more pressure.
Buoyancy
Water pushes up more on the bottom of an object than on the top, so the object feels an upward lift.
Archimedes' Principle
A fluid pushes up exactly as much as the displaced fluid would weigh.
Thermal Equilibrium
When two objects stop getting warmer or cooler because they have matched temperatures, they are in thermal equilibrium.
Specific Heat Capacity
Some substances warm up quickly, while others need much more energy for the same temperature change.
Ideal Gas Law
If you squeeze a gas, heat it, or add more particles, the other gas properties must adjust in a predictable way.
Position
Where something is, described by numbers from some starting point.
Displacement
How far you are from where you started, in a straight line. Not the path you took.
Velocity
How fast something is moving AND which way it's heading—direction is essential.
Speed
How fast you're going, ignoring which way—just the magnitude of motion.
Acceleration
How quickly your speed (or direction) is changing. The 'push back' you feel when a car speeds up.
Free Fall
A dropped ball accelerates at the same rate regardless of its mass.
Projectile Motion
A thrown ball follows a curved path—horizontal motion is steady, vertical is accelerated.
Circular Motion
A car on a circular track at constant speed is still accelerating—toward the center.
Reference Frame
Are you 'moving' on a train? Depends on whether you ask someone on the train or the platform.
Vectors
An arrow pointing somewhere with a certain length—the length is 'how much,' the direction is 'which way.'
Angular Velocity
How fast something is spinning — a car wheel spinning fast has high angular velocity.
Average Speed
It tells you how fast the trip was overall, not how fast you moved at each moment.
Instantaneous Speed
It is what a speedometer shows right now, not over the whole trip.
Relative Velocity
How fast something seems to move depends on who is watching.
Gravitational Field
A planet creates an invisible pull around it. The closer you are, the stronger that pull is.
Orbital Motion
An orbit is like falling around a planet instead of straight down onto it.
Escape Velocity
It is the launch speed needed so gravity cannot pull the object back forever.
Speed of Light
Light moves incredibly fast, but not infinitely fast.
Visible Light
Visible light is just the slice of electromagnetic waves our eyes happen to notice.
Polarization
A polarizing filter only lets through certain vibration directions.
Total Internal Reflection
At a steep enough angle, light gets trapped and bounces inside the material.
Mirrors
A mirror sends light back in a predictable way, so your eye traces the rays and sees an image.
Lenses
A lens bends light on purpose so an image can be focused or spread out.
Ray Diagram
Instead of tracing every ray of light, you trace only the key rays that tell you where the image must be.
Image Formation
Your eye or a screen sees an image based on where the outgoing rays meet or appear to meet.
Redshift
When light is stretched, it shifts toward the red end of the spectrum.