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from vpython import *

scene.caption = """Right button drag or Ctrl-drag to rotate "camera" to view scene.
To zoom, drag with middle button or Alt/Option depressed, or use scroll wheel.
     On a two-button mouse, middle is left + right.
Touch screen: pinch/extend to zoom, swipe or two-finger rotate."""

side = 4.0
thk = 0.3
s2 = 2*side - thk
s3 = 2*side + thk
wallR = box (pos=vector( side, 0, 0), size=vector(thk, s2, s3),  color = color.red)
wallL = box (pos=vector(-side, 0, 0), size=vector(thk, s2, s3),  color = color.red)
wallB = box (pos=vector(0, -side, 0), size=vector(s3, thk, s3),  color = color.blue)
wallT = box (pos=vector(0,  side, 0), size=vector(s3, thk, s3),  color = color.blue)
wallBK = box(pos=vector(0, 0, -side), size=vector(s2, s2, thk), color = color.gray(0.7))

ball = sphere (color = color.green, radius = 0.4, make_trail=True, retain=100, 
               trail_color=color.cyan)
ball.mass = 1.0
ball.p = vector(-0.15, -0.23, +0.27)

side = side - thk*0.5 - ball.radius

dt = 0.5
t = 0.0
while True:
    rate(100)
    t = t + dt
    ball.pos = ball.pos + (ball.p/ball.mass)*dt
    if not (side > ball.pos.x > -side):
        ball.p.x = -ball.p.x
    if not (side > ball.pos.y > -side):
        ball.p.y = -ball.p.y
    if not (side > ball.pos.z > -side):
        ball.p.z = -ball.p.z