I've got 2 boxes (2D, so squares), each with a RigidBody2D and a BoxCollider2D. Both have a physics material that has a friction of 1, and a bounce of 0. Both have a mass of 1, gravity scale of 1 and linear and angular drag of 0.5. When I stack them, and click and drag the bottom box side to side, the top box doesn't move. It's as if there's no friction at all between the 2 GameObjects. I've played round with the RigidBody2D's drag values and the friction value of the Physics material, but there's no change in behaviour. I don't want to create a joint between the two, because it's possible to click and drag the top box, in which case the bottom box should move independently. Does anyone have any idea on what's causing the top box to not move, or how to overcome it?