Learn physics from first principles to frontier ideas
1113 topics across 21 areas, each with plain explanations, formulas, worked examples and live interactive simulations.
Browse all topics · Interactive labs · Quizzes · Timed tests
Who it is for
Build the core ideas in order, from measurement and motion to energy and forces, with plain-language explanations and a worked example for each topic.
Use the quizzes and timed tests to find weak areas, then go back to the matching topic and its formula until the mistake stops happening.
Point learners to a single explanation, a live simulation and a common-mistake note for any topic, instead of writing new material for every lesson.
Move from beginner to advanced topics at your own pace, with progress saved in your browser and no account needed.
Follow a clear path through the subject with short explanations, a real-world use for each topic and quizzes to check understanding, without needing a tutor on hand.
Refresh a half-remembered formula or concept quickly, then use the FAQ and common-mistake notes to see where students usually go wrong.
Explore by area
Common questions
Where should a complete beginner start?
Start with Measurement & Math Tools, then Kinematics and Newton's Laws. Filter topics by the Beginner level and use the labs to see ideas in motion.
How much maths do I need?
Beginner topics need arithmetic, basic algebra and graphs. Intermediate topics add trigonometry, vectors and basic calculus. Advanced topics use differential equations, linear algebra and complex numbers.
What is the difference between mass and weight?
Mass is the amount of matter and is the same everywhere. Weight is the gravitational force on that mass (W = mg), so it changes with location.
Why do heavy and light objects fall together?
Gravitational force grows with mass, but so does inertia. The two cancel, so every object accelerates at g in a vacuum.