Challenge: River rocks

Make more realistic water particles and interactive repelling rocks.

More realistic forces

Hint

var Repeller = function(x, y) {
// change something here
};
var Particle = function(position) {
// change something here
};

This program uses a particle system and a repeller to simulate a river flowing around a single rock.
To start off with, make it a bit more realistic by decreasing the force of the rock and the initial vertical velocity of the
water particles. They seem to be moving a bit too much now!