Using it

Install

macOS and Linux

curl -fsSL https://askphysics.vercel.app/install.sh | bash

Windows (PowerShell)

irm https://askphysics.vercel.app/install.ps1 | iex

Homebrew (macOS and Linux)

brew install shankar-sachin/tap/askphysics

The installers put askphysics in its own environment with uv and never touch your system Python. Uninstall with uv tool uninstall askphysics (or brew uninstall askphysics). Every way to install is on askphysics.vercel.app/installers.

Or skip installing and use the website, askphysics.vercel.app, which runs the same package inside your browser (with the fake model for now; see the FAQ).

Ask a question

askphysics ask "How fast does a falling object hit the ground if it is dropped from 20 m?"

Quotes are optional. Useful options:

Get the models

You don't have to do anything. The installers and Homebrew download tellus and solem when they install (about 66 MB, once), and any install, pip included, downloads whichever of them is missing on your first askphysics ask, with a progress display. They are kept in ~/.cache/askphysics/models/ (or the folder ASKPHYSICS_MODEL_DIR names; Homebrew keeps them in its own var folder), so it happens once.

Every file is checked against the sizes and hashes this version of Ask Physics pins, and anything that doesn't match is refused. Set ASKPHYSICS_AUTO_PULL=0 to stop the downloads that happen while you ask. If a download fails, ask still answers (with a stand-in) and says why, and the next ask tries again. Without models, ask uses a stand-in that only knows "dropped from a height" questions, and says so.

celeste asks first

tellus and solem are small and every question needs them. celeste (about 240 MB) is the last resort when solem can't make a plan work, and most questions never get that far, so it never downloads by itself. When a question does reach it, askphysics ask on a terminal asks:

? This question needs celeste-1 (about 240.1 MB, a one-time download) to try harder.
  [y] yes   [N] no   [a] always download   [never] don't ask again
  Download it?

y downloads it now (with a progress display) and carries on with it; n or Enter skips celeste for this question and doesn't ask again during it. a and never are remembered in a small file, preferences.json, in the models folder (~/.cache/askphysics/models/, or ASKPHYSICS_MODEL_DIR); to reset the choice, delete that file. You can also set ASKPHYSICS_CELESTE_DOWNLOAD=ask, always, or never, which wins over the file.

With --json, in a script (no terminal), and on the website, nothing is ever asked: celeste is skipped unless it is already installed or your saved choice is always.

Other commands

Next: Reading an answer.