<?xml version="1.0" ?>
<sdf version="1.6">
  <world name="default">
    <model name="ground_plane">
      <static>true</static>
      <link name="link">
        <collision name="collision">
          <geometry>
            <plane>
              <normal>0 0 1</normal>
              <size>100 100</size>
            </plane>
          </geometry>
        </collision>
        <visual name="visual">
          <cast_shadows>false</cast_shadows>
          <geometry>
            <plane>
              <normal>0 0 1</normal>
              <size>100 100</size>
            </plane>
          </geometry>
        </visual>
      </link>
    </model>
    <model name="sphere">
      <link name="link0">
        <pose>0 0 0.5 0 0 0</pose>
        <collision name="sphere_collision">
          <geometry>
            <sphere><radius>1</radius></sphere>
          </geometry>
        </collision>
        <visual name="sphere_visual">
          <geometry>
            <sphere><radius>1</radius></sphere>
          </geometry>
        </visual>
        <inertial>
          <mass>0.1</mass>
        </inertial>
      </link>
      <link name="link1">
        <pose>0 1 0.5 0 0 0</pose>
        <collision name="sphere_collision">
          <geometry>
            <sphere><radius>1</radius></sphere>
          </geometry>
        </collision>
        <visual name="sphere_visual">
          <geometry>
            <sphere><radius>1</radius></sphere>
          </geometry>
        </visual>
        <inertial>
          <mass>1</mass>
        </inertial>
      </link>
      <link name="link2">
        <pose>1 0 0.5 0 0 0</pose>
        <collision name="sphere_collision">
          <geometry>
            <sphere><radius>1</radius></sphere>
          </geometry>
        </collision>
        <visual name="sphere_visual">
          <geometry>
            <sphere><radius>1</radius></sphere>
          </geometry>
        </visual>
        <inertial>
          <mass>2</mass>
        </inertial>
      </link>
      <link name="link3">
        <pose>1 1 0.5 0 0 0</pose>
        <collision name="sphere_collision">
          <geometry>
            <sphere><radius>1</radius></sphere>
          </geometry>
        </collision>
        <visual name="sphere_visual">
          <geometry>
            <sphere><radius>1</radius></sphere>
          </geometry>
        </visual>
        <inertial>
          <mass>3</mass>
        </inertial>
      </link>
    </model>
  </world>
</sdf>
