question about the manual-"Simulating the physics scene

I try to cut and past the example in that chapter like this:

from direct.directbase import DirectStart
from pandac.PandaModules import OdeWorld, OdeBody, OdeMass, Quat

# Load the cube where the ball will fall from
cube = loader.loadModel("box.egg")
cube.setColor(0.2, 0, 0.7)

# Load the smiley model which will act as our iron ball
sphere = loader.loadModel("ball.egg")
sphere.setPos(10, 1, 21)
sphere.setColor(0.7, 0.4, 0.4)

# Setup our physics world and the body
world = OdeWorld()
world.setGravity(0, 0, -9.81)
body = OdeBody(world)
M = OdeMass()
M.setSphere(7874, 1.0)

# Set the camera position
base.disableMouse(), -20, 40), 0, 10)

# Create an accumulator to track the time since the sim
# has been running
deltaTimeAccumulator = 0.0
# This stepSize makes the simulation run at 90 frames per second
stepSize = 1.0 / 90.0

# The task for our simulation
def simulationTask(task):
  global deltaTimeAccumulator
  # Set the force on the body to push it off the ridge
  body.setForce(0, min(task.time**4 * 500000 - 500000, 0), 0)
  # Add the deltaTime for the task to the accumulator
  deltaTimeAccumulator += globalClock.getDt()
  while deltaTimeAccumulator > stepSize:
    # Remove a stepSize from the accumulator until
    # the accumulated time is less than the stepsize
    deltaTimeAccumulator -= stepSize
    # Step the simulation
  # set the new positions
  sphere.setPosQuat(render, body.getPosition(), Quat(body.getQuaternion()))
  return task.cont

taskMgr.doMethodLater(1.0, simulationTask, "Physics Simulation")


But the ball fall through the box, I thought the iron ball will rolling on the box or jumping somethiing…,and I saw the section is incomplete, is the example incomplete? Or there is a special setup about my box and ball model?(which is exported from blender)

my environment:
panda3d 1.5.4
ubuntu 7.10

Actually, this sample is not to show how collisions work, but it’s just to show how to write code to step the ODE simulation the right way.

At the next page, about Collision Detection, you can find a sample that actually enables collisions.

Ok, Thanks!