mujoco

<mujoco>
  <option cone="elliptic" timestep="1e-4" integrator="implicitfast"/>

  <visual>
    <global elevation="0"/>
  </visual>

  <asset>
    <texture name="grid" type="2d" builtin="checker" rgb1=".1 .2 .3" rgb2=".2 .3 .4" width="300" height="300"/>
    <material name="grid" texture="grid" texrepeat="8 8" reflectance=".2"/>
    <texture name="ball" type="cube" builtin="checker" rgb1=".3 .3 .3" rgb2="1 1 1" width="300" height="300"/>
    <material name="ball" texture="ball" texrepeat="8 8"/>
  </asset>

  <worldbody>
    <geom name="floor" size=".2 .2 .01" type="plane" material="grid"/>
    <geom name="wall" size=".2 .2 .01" type="plane" material="grid" pos=".2 0 .2" zaxis="-1 0 0"/>
    <light pos="0 0 .6"/>
    <light pos="-.6 0 .6" dir="1 0 -1"/>
    <body name="ball" pos="-.1 0 .2">
      <freejoint/>
      <geom name="ball" type="sphere" size=".02" material="ball" mass=".001"/>
      <body name="ballast">
        <joint type="ball" stiffness="0.1" damping=".0001"/>
        <geom name="ballast" type="sphere" size=".02" contype="0" conaffinity="0" mass=".01" group="3"/>
      </body>
    </body>
  </worldbody>

  <default>
    <pair solref="-100000 0" solreffriction="0 -10000"/>
  </default>

  <contact>
    <pair geom1="floor" geom2="ball"/>
    <pair geom1="wall" geom2="ball"/>
  </contact>

  <keyframe>
    <key name="throw" qvel="1.3 0 0 0 0 0 0 0 0"/>
  </keyframe>
</mujoco>