Physics Command Tab

  

In this sub-menu, you can enable/disable global physical properties (toggle physics, collisions and gravity), as well as enable/disable actors' physical properties.

This sub-menu gives you access to advanced physics, which are desbribed here (see the video at the bottom of the linked page for a better understanding of the different functionnalities available). Make sure that you have correctly selected the actors that you want before toggling freeze, gravity or physics on them.