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Six branches of physics, from the ground up.
Featured articles
Start here — one clear explainer from each branch.
Circular Motion and Centripetal Force
Circular motion needs a centre-seeking force: centripetal force, F = mv²/r. Learn why objects turn, what supplies the force, and how to calculate it.
Acceleration Explained
Acceleration is the rate of change of velocity. Learn what it means, how to calculate it with a = Δv/t, and why slowing down and turning count too.
Capacitors and Capacitance
Understand capacitors, capacitance, how they store charge and energy, and why they are used in circuits from camera flashes to power supplies.
Entropy Explained
Learn what entropy is, why disorder tends to increase, and how the second law of thermodynamics limits engines and every real process.
Interference and Diffraction
Learn how waves interfere, what diffraction is, why double-slit fringes form, and how diffraction limits the detail of any optical instrument.
Quantum Computing Basics: Qubits and Superposition
Learn the basics of quantum computing: qubits, superposition, entanglement and measurement, and what quantum computers can and cannot do.
Popular calculators
Type in numbers, get the answer with the working shown.
Banked Curve Calculator
Find the ideal banking angle for a curved road, or the speed a vehicle can hold on a banked bend without any friction helping it.
Buoyancy Calculator
Find the upward buoyant force on a submerged object from the fluid density and the volume of fluid that it displaces when immersed.
Centripetal Force Calculator
Find the inward force needed to keep an object moving in a circle, or the speed it gives for a known inward force around the circle.
Circular Motion Calculator
Find centripetal acceleration, angular speed and orbital period for an object moving steadily around a circular path at constant speed.
Escape Velocity Calculator
Find the speed an object needs to escape a planet's gravity forever, worked out from the planet's mass and radius alone.
Gravitational Field Calculator
Find the strength of gravity at a distance from a planet or star, or the mass that produces a given field strength at that point.
Gravitational Potential Energy Calculator
Find the stored energy of an object raised above the ground, or the height or mass behind a known amount of energy held at that height.
Hooke's Law Calculator
Find the force needed to stretch or compress a spring, or its extension or spring constant from a known applied force within its elastic limit.
Impulse and Momentum Calculator
Find the impulse from a force acting over time, or the change in momentum from a mass and its change in velocity during the push.
Kinetic Energy Calculator
Find the kinetic energy of a moving object, or work backwards to its speed or mass from a known amount of energy stored in its motion.
Momentum Calculator
Find the momentum of a moving object, or work out its velocity or mass from a known value of momentum for the object in motion.
Net Force Calculator
Add the forces acting on an object to get the net force, then find the acceleration that net force produces in the object.
Play and learn
Simulators, quizzes and games — physics you can touch.
Physics Quiz Challenge
Test your physics knowledge across six topics with 60 original questions, instant explanations, progress tracking, and a score to beat.
Projectile Motion Simulator
Launch a projectile, adjust angle and speed, watch the trajectory unfold, and try to hit the target flag downrange in this simulator.
Pendulum Simulator
Swing a pendulum on Earth, the Moon or Jupiter. Change the string length and gravity and watch the period change live as it swings.
Wave Interference Visualiser
Two wave sources, one pattern: explore constructive and destructive interference and reveal the nodal lines in this animated visualiser.
Circuit Builder
Build a series or parallel circuit with up to three resistors and see resistance, current, voltage and power update live.
Physics Unit Converter
Convert length, mass, time, energy, temperature and speed instantly — with the exact factors physicists use for homework and lab work.