Processing: Creative Coding and Computational Art

PROCESSING: CREATIVE CODING AND COMPUTATIONAL ART
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class Ball{
float x, y, r, m;
// default constructor
Ball() {
}
Ball(float x, float y, float r) {
this.x = x;
this.y = y;
this.r = r;
m = r*.1;
}
}
If it isn’t obvious, all I added was a mass property to the class and based its value on the
radius. Of course, the mass could also be coded as a completely separate value from
the radius, as, for example, a large cork ball would certainly weigh less than a much
smaller steel ball bearing. That being said, tying the mass to the radius was easiest.
The checkObjectCollision() function is where the majority of changes are, and of course
it’s where the scary conservation of momentum expressions are coded:
void checkObjectCollision(Ball[] b, Vect2D[] v){
float d = dist(b[0].x, b[0].y, b[1].x, b[1].y);
if (d < b[0].r + b[1].r){
/* calculate final velocities based on
Law of Conservation of Momentum */
float finalVel0 = ((b[0].m - b[1].m) * v[0].vx + 2 *➥
b[1].m * v[1].vx) / (b[0].m + b[1].m);
float finalVel1 = ((b[1].m - b[0].m) * v[1].vx + 2 *➥
b[0].m * v[0].vx) / (b[0].m + b[1].m);
v[0].vx = finalVel0;
v[1].vx = finalVel1;
}
}
Hopefully, you didn’t find the long expressions too frightening; they’re long but pretty
straightforward, and of course there’s no obligation to really understand why they work
(but then I’m not your Physics teacher). Following the new expressions, I simply assign the
final velocities to the original velocity variables.