createCanvas(600, 400);

}

​

function draw() {

  background(100);

  fill("white");

  stroke("white");

​

​

  // Sinusoid moves a circle up and down

  var myOffset = height / 2;

  var myAmplitude = 100;

  var myFrequency = 1; // beats per second

  var myPhase = 0;

​

  line(0, myOffset, width, myOffset);

​

​

  var circleY = myOffset + myAmplitude * sin(TWO_PI * (millis() / 1000.0) * myFrequency + myPhase);

  circle(75, circleY, 50);

​

​

  stroke("yellow");

  line(0, myOffset - myAmplitude, width, myOffset - myAmplitude);

  line(0, myOffset + myAmplitude, width, myOffset + myAmplitude);

​

}