Physics-Enabled 3D Design App

I need a prototype desktop or web application that lets secondary-school students create 3D projects and immediately test their ideas with built-in physics simulation. Circuit design was an early thought, yet my priority now is a smooth 3D workspace that shows real-time forces, collisions, gravity and basic material behaviour so each student can see whether a concept would work in the physical world.

Core requirements
• A simple modelling canvas where users can add, move and resize primitive shapes or imported meshes.
• A physics engine (Bullet, PhysX, Havok, or an open-source alternative) already wired in, offering toggles for gravity, mass, friction and constraints.
• One-click simulation: hit “Run” and watch live feedback—velocity vectors, stress points, centre of mass, etc.
• Project saving/loading to local storage or the cloud so teachers can review work and identify standout talent.
• Clean, child-friendly UI; think drag-and-drop panels, colour-coded properties, undo/redo.

What I will accept as done
1. An installable or browser-based MVP that runs on current Windows machines in a standard school lab environment.
2. Source code with build instructions.
3. A short PDF or walkthrough video showing a sample model going from edit mode to physics simulation in under five minutes.

Please tell me which framework or game engine you plan to use (Unity, Godot, Three.js, etc.) and how you will keep performance smooth on mid-range hardware. If you have demos of prior simulation work, include the link.