Colliders define an approximate shape for an object that’s used by the physics engine to determine collisions with other objects.
2D colliders all have names ending ‘2D’. A collider named without a ‘2D’ ending is a 3D joint. Note that you can’t mix 3D game objects and 2D colliders or 2D game objects and 3D colliders.
The collider types that can be used with Rigidbody 2D are:
See the pages about these components for further details.
USE AUTO MASS:
Note that a Collider’s mass determines the Rigidbody’s mass if you have Use Auto Mass selected. This option is good to use in conjunction with the Buoyancy Effector 2D.