I wouldn't recommend using physics for this since you don't want gravity, and you don't want the object to be movable. What you can do is create a script that just makes an object move in the way you want. before anyone here can help you do that, however, we will need some more information about what you are trying to accomplish.
Is this a 2d game or a 3d game? Is the ground flat? Is the object shaped the same as the ground?
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