Particle fluid
This applet simulates a system of particles which repel each other at close
distances and attract each other when they're far away. You can click on
a particle and drag it around with an 'elastic' line. Right clicking adds
a blue repelling particle. Hitting the 'r' key
will reset the particles to a random configuration.
Other keys:
g: decrease gravity
G: increase gravity
d: decrease particle distance
D: increase particle distance
f: decrease interparticle force strength
F: increase interparticle force strength