How hard is it for the average Jedi to move objects? Like what are their limitations? How hard do they have to concentrate to use it to move a 20 pound rock for example? Legends and Canon allowed.
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Generally speaking the ease in which one can use the force has to do the midichlorian count.
As we can see in this question and answers the Force users with a higher midichlorian count are shown to be able perform greater feats. Who is the most powerful user of the Force?
As with anything, the amount of dedication a single user puts into their training will also be a factor. There seems to be no implied limit on how a Force user can manipulate physical objects.