Drag the paper to any height with your mouse or finger, then release to watch it fall. A flat sheet has enormous drag relative to its tiny mass, creating the slow drifting fall we see in real life. Switch to edge-on and the same sheet slices through air much faster.
Grab the paper and drag it anywhere in the simulation area, then let go to start the fall. Adjust size, weight (gsm = grams per square metre), and orientation using the controls. Demo mode cycles through preset scenarios automatically. After 10 seconds of inactivity demo starts on its own.
Each frame solves F = ma with gravity F = mg downward and aerodynamic drag F = ½ρCdAv² upward. Air density ρ = 1.225 kg/m³. Paper mass = area × (gsm/1000). Drag coefficient Cd: flat = 1.28, angled = 0.75, edge = 0.1. Terminal velocity = √(2mg / ρCdA). The world is fixed at 10 metres tall.
Mouse and touch events are unified. A pointer down on or near the paper begins a drag. On release the paper's canvas position is converted back to world coordinates and the physics simulation starts from there with zero initial velocity.
Throw velocity from flick gestures, wind effects, multiple simultaneous sheets for side-by-side comparison, and a 3D WebGL tumble view would all be natural extensions.