Drag to spawn objects, watch live energy and momentum numbers update in real time, and read explanations that scale from "Curious" to "Expert" — no textbook required.
No install, no signup. The free demo runs entirely in your browser.
A real physics engine, a real-time readout panel, and explanations that grow with you.
Click and drag in empty space — the size of your drag becomes the size of the body. Boxes, balls, polygons, ropes. Six tools, no menu-diving.
Speed, momentum, kinetic and potential energy, angular velocity — for the selected body and the whole system. Watch energy conservation play out.
Curious / Student / University / Expert. Same simulation, different language — from "things bounce off each other" to the impulse-momentum tensor formulation.
Two unlocks. One price. No subscription.
Build something good? Save the world to a JSON file and reload it later — keep your demos, your puzzles, your "I broke physics" moments. Scenes are yours, stored locally; we never see them.
Every concept you encounter while playing — collisions, torque, conservation laws, oscillations — exports as a printable HTML doc with university and expert-level explanations and the formulas that go with them.
Free to use forever. Pro is one payment for the lifetime of the app.
Secure checkout via Stripe. The free edition has every simulation feature.
Any modern desktop or mobile browser. Tested on Chrome, Firefox, Safari, and Edge. There's also an Android app via Google Play (coming v1.1) that wraps the web build.
Yes — install it as a PWA ("Add to Home Screen" on mobile, or the install icon in your desktop browser's address bar) and it runs locally with no network needed.
Full refund within 14 days, no questions asked. Email support@stacklis.com with your Stripe receipt and the refund goes through within a business day.
The $9 one-time covers personal use across your devices. For classroom or school-wide deployments, email support@stacklis.com — we're happy to work something out, including teacher comp licenses.
None. No analytics, no tracking, no telemetry. Pro state lives in your browser's localStorage. Stripe handles payment and never shares card data with us. Full details in the privacy policy.
Coming as v1.1. The web app installs as a Progressive Web App on Android in the meantime — Chrome will offer the install prompt, or use the menu's "Install app" option.
The client-side simulator is open and inspectable on GitHub (link in the footer). The Pro unlock is honor-system: we trust you. If the simulator is useful to you, the $9 pays for ongoing maintenance.
Maybe, eventually, for new buyers. If you've already bought Pro, you keep it at no extra cost — including all v1 updates.