# Revision history [back]

This is caused by the fact that DART, by default, uses the FCL collision library with a configuration that changes simple shapes like sphere into a mesh. In your case, the resulting mesh doesn't have enough resolution to correctly behave as a sphere. You can change the DART's collision detector to bullet and you should get better behavior in your example. You'd that by setting the dart_collision_detector parameter (http://sdformat.org/spec?ver=1.7&elem=physics#dart_collision_detector)

<?xml version="1.0" ?>
<sdf version="1.7">
<world name="default">
<physics type="dart">
<dart>
<collision_detector>bullet</collision_detector>
</dart>
</physics>
...
</world>
</sdf>