import pybullet as p
import time

p.connect(p.GUI)
cube2 = p.loadURDF("cube.urdf",[0,0,3], useFixedBase=True)
cube = p.loadURDF("cube.urdf", useFixedBase=True)
p.setGravity(0,0,-10)
timeStep = 1./240.
p.setTimeStep(timeStep)
p.changeDynamics(cube2,-1,mass=1)
#now cube2 will have a floating base and move

while (p.isConnected()):
	p.stepSimulation()
	time.sleep(timeStep)