About Theory in Play

Theory in Play is a free collection of 92 interactive physics simulations. Change a variable, watch the result, and follow the explanation to connect an equation with what it describes.

Learn by experimenting

Start with a prediction. Change one variable at a time, compare the outcome, then replay the guided stages. The branch collections and guided tours connect related ideas.

Models and their limits

These are educational models. Each experiment makes simplifying assumptions described in its lesson. A simulation is useful within those assumptions; it is not a substitute for experimental measurements or an engineering safety calculation.

The homepage Moon follows a calculated elliptical orbit with mean lunar parameters. It is not a live astronomical ephemeris. Display distances and sizes are adjusted by default; the orbit panel explains the model and offers a true-scale view.

Artwork and credits

Earth and Moon textures use NASA imagery and the Three.js example texture collection. NASA does not endorse this site. Decorative experiment artwork is illustrative; the interactive diagrams are computed by the simulations.

NASA Moon imagery · NASA Earth at night · Three.js license · Manrope license · Outfit license