[00]The rig
a small world with four walls and a downward pull
Engine
2D verlet-ish · gravity, walls, floor, disc-disc collisions
Mass
size = mass · big discs shove little ones
Input
grab nearest disc · drag tracks velocity · release throws it
Restitution
bounce ≈ 0.62 · floor friction settles them
Idle
autopilot taps a random disc every couple seconds
Status
🟢 grounded · contrast AA · reduced-motion lets them rest
[01]Six forces
the physics vocabulary, one law at a time · scroll to reveal
01 · gravity
Down is real
Every disc accelerates downward each frame and lands on the floor. The hero above is the full sandbox — go grab one.
02 · collision
Things hit things
Equal and opposite.
03 · mass
Bigger means heavier
Radius is mass, so the large disc barely flinches when the small one strikes it.
04 · restitution
How much bounce
A coefficient between dead-stop and perfect rebound — tune it live below.
05 · palette
Toy primaries
Red, mustard, teal, blue.
06 · momentum
The only one you can break
Nine experiments responded to the pointer. This is the first you can grab — drag stores velocity, release hands it to the disc, and it flies.
[02]Bounce
drag to set restitution · low = beanbags, high = superballs · grab these too
restitution
62
Field note: no physics library — a few hundred lines of Euler integration with positional correction so discs don't sink through each other. The "weight" you feel when you fling one is just velocity sampled from your drag and handed back on release. Touch as the final voice in the set.