Prefab Sphere floating away

Hi, I have two sphere GameObjects as prefabs. They have rigidbodies attached. I want them to stay put on a surface but interact with each other when they collide (push each other around, bounce off each other, blah blah). However, in the game view, when I drag in a prefab, and the rigidbody "use gravity" checkbox is turned off, the objects float away! I don't want this so I turned on "use gravity." Now, they get placed into the scene but still take a long time to settle down into the floor and when I drag them around, they can still kind of float around there. How do I just get them to stay on the surface but interact with each other? I'm not quite sure what isKinematic does but I toggled it and it didn't seem to fix my issue.