submission by SSample for make a scene using some motion (View the other submissions)
function setup(){
  var myCanvas = createCanvas(800, 800); //you must keep this line unmodified
  rocky_x = [ ] 
  rocky_y = [ ]
  spot = 590

  for(i = 0; i < 20; i ++) {
    rocky_x[i] = random(width)
    rocky_y[i] = random(200, 600)
  }
}

function draw() {
  background('blue')
  stroke('lime')
  fill('lime')
  rect(0, 0, width, 200)
  rect(0, 600, width, 200)
  for(i = 0; i < rocky_y.length; i++) {
    thisx = rocky_x[i]
    thisy = rocky_y[i]
    rocky_y[i] += random(0, 5)
    if(rocky_y [i] > spot) {
      rocky_y [i] = 0
    }
      stroke('black')
      fill('brown')
      ellipse(thisx, thisy, 20, 10)
  }
  stroke('brown')
  arc(400, 490, 50, 25, 0, PI)
  fill('black')
  stroke('black')
  rect(395, 455, 5, 35)
  fill('white')
  stroke('white')
  triangle(395, 455, 395, 485, 375, 470)
}