In سَوْفَ, wāw is sākin after fatḥah: a līn letter, not a madd wāw that automatically receives two counts in ordinary connection.
In تَعْلَمُونَ, wāw is sākin after ḍammah: a madd letter. In connection it carries natural madd; when stopping at the verse ending, the nūn becomes sākin and madd ʿāriḍ li-s-sukūn applies.
Compare the two wāws rather than assigning them the same ruling.
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Sawfa and taʿlamūn: līn versus madd
Al-ʿAṣr and At-Takāthur: Applied Ghunnah, Madd, Lām and Waqf
In سَوْفَ, wāw is sākin after fatḥah: a līn letter, not a madd wāw that automatically receives two counts in ordinary connection.
In تَعْلَمُونَ, wāw is sākin after ḍammah: a madd letter. In connection it carries natural madd; when stopping at the verse ending, the nūn becomes sākin and madd ʿāriḍ li-s-sukūn applies.
Compare the two wāws rather than assigning them the same ruling.