mujoco

<mujoco>
  <option integrator="implicitfast" viscosity="2" sleep_tolerance="0.1">
    <flag sleep="enable"/>
  </option>

  <worldbody>
    <geom type="plane" size="5 5 .01"/>

    <!-- constrained flex on the floor, will go to sleep quickly -->
    <body name="flex_body" pos="0 0 0.01">
      <flexcomp name="f1" type="grid" dim="1" count="3 1 1"
                spacing=".05 .05 .05" radius=".01" mass="1">
        <edge equality="true" solref="0.15 0.2"/>
      </flexcomp>
    </body>

    <!-- ball that will collide with the flex -->
    <body name="ball" pos="0 0.01 0.5">
      <freejoint/>
      <geom type="sphere" size=".05"/>
    </body>
  </worldbody>
</mujoco>