class Pendulum{ float theta_0; float theta; PVector leng = new PVector(0,0); float g = 9.8; int conv = 4000000; //conversion factor from physics units to pixels Pendulum(float length_, float theta_0_){ theta_0 = theta_0_; leng.y = length_; } void update(float time){ theta = theta_0*cos(sqrt(g/leng.mag())*time); } void render(){ pushMatrix(); translate(width/2,0); rotate(theta); line(0,0,conv*leng.x,conv*leng.y); ellipse(conv*leng.x,conv*leng.y,10,10); popMatrix(); } }

Pendulum p; float t = 0.0; ArrayList pends; float[] lengths = new float[30]; float g = 9.8; void setup(){ size(400,400); lengths[0] = 0.00009; for(int i=1;i<30;i++){ //arrange lengths so frequency difference between pendulums is constant lengths[i] = g*lengths[i-1]/( g + 4*PI*PI*lengths[i-1] + 4*PI*sqrt(g*lengths[i-1]) ); } pends = new ArrayList(); for(int i=0; i<30; i++){ p = new Pendulum(lengths[i],0.2); pends.add(p); } smooth(); } void draw() { background(255); //update current time t+=0.0002; for(int i = 0;i<pends.size();i++){ p = (Pendulum) pends.get(i); // fetch position of current pendulum at time t p.update(t); // draw pendulum p.render(); } }

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A quick and rough recreation of the Pendulum Waves demonstration made popular lately the Havard lecture demonstration video:

http://bit.ly/mScLo8

Shows lots of nice beat patterns coming and going and also at time reminiscent of the 'Spinning Dancer' illusion.

Blog post: http://www.cutsquash.com/blog/?p=62

9 Sep 2012