def setup():
    size(900, 450)

def draw():
    t = 0.01*frameCount
    g = 9.8
    L = 2.0
    degree = PI/180
    amplitude = 20*degree
    omega = sqrt(g/L)
    theta = amplitude * sin(omega*t)
    xbob = L * sin(theta)
    ybob = L * cos(theta)
    # convert coordinates into pixel coordinates
    xpixel_pivot = 0.5*width
    ypixel_pivot = 0.1*height
    scale = 100.0  # pixels per meter
    xpixel_bob = xpixel_pivot + scale*xbob
    ypixel_bob = ypixel_pivot + scale*ybob
    # clear the screen for each new frame of animation
    background(128)
    # draw the string
    line(xpixel_pivot, ypixel_pivot, xpixel_bob, ypixel_bob)
    # draw the bob
    ellipse(xpixel_bob, ypixel_bob, 20, 20)