Reference for Educators

The Feynman Lectures on Physics
All three volumes of Richard Feynman's celebrated lecture series, freely available online from Caltech. Covers mechanics, radiation, heat, quantum mechanics, and electromagnetism.
OpenStax Physics Textbooks
Free, peer-reviewed college-level physics textbooks from Rice University, including University Physics Vol. 1–3 and College Physics. Downloadable in PDF or available online.
LibreTexts Physics
A large, freely accessible library of open physics textbooks ranging from introductory to graduate level. Covers classical mechanics, electromagnetism, thermodynamics, quantum mechanics, and more.
Light and Matter
A free introductory physics textbook by Benjamin Crowell, covering all standard topics in a clear, accessible style.

PhET Interactive Simulations
Research-based, free interactive physics and science simulations from the University of Colorado Boulder. Covers mechanics, electricity, waves, optics, quantum phenomena, and more. Widely used in classrooms worldwide.
3JCN Physics Simulations
Over 350 free, interactive 3D physics simulations for students and instructors, covering mechanics, waves, electricity and magnetism, optics, modern physics, astronomy, and more.

HyperPhysics
An extensive, concept-map-based physics reference from Georgia State University. An excellent quick-reference tool for educators and students at all levels.
The Physics Classroom
Free tutorials, concept builders, and interactive simulations covering high school and introductory college physics. Well-organized by topic with clear explanations.
MIT OpenCourseWare — Physics
Free MIT course materials including lecture notes, problem sets, exams, and lab guides for physics courses ranging from classical mechanics to quantum field theory.

Science Buddies — Physics Experiments
Detailed, step-by-step physics experiment guides with materials lists and background reading. Useful for science fair projects and classroom demonstrations.

NIST Physics
The National Institute of Standards and Technology physics portal. Authoritative source for physical constants, measurement standards, atomic data, and fundamental research.
National Physical Laboratory
The UK's National Standards Laboratory in Teddington, Middlesex. Reference resource for measurement science, physical constants, and standards.
American Association of Physics Teachers
Professional organization for physics educators. Offers curriculum resources, lab guides, teaching materials, and information on physics education research.
NASA STEM Engagement for Educators
Free astronomy and space science resources from NASA, including lesson plans, activities, and multimedia materials for classroom use.