There is a difference in the difficulty by which the two different objects can be lifted up.
Is “by” correct here? Does “difficulty by which” sound natural? is there maybe a better alternative?
Thanks a lot in advance!
This is a question about what preposition to use with “difficulty”. It is being confused by introducing the relative pronoun “which” and the relative clause. So let’s get rid of the “which”. Would you say
Lift an object with difficulty
Lift an object by difficulty
Clearly the first. So this is not a question about “which” but a question about what preposition to use with a particular noun. The point to learn from this is that you should always try to cut the problem down to the bare essentials as this will make it easier to answer and easier to learn from the answer.