In يَوْمَ, wāw is sākin after fatḥah, making it a letter of līn, not wāw madd. In «يَكُونُ», wāw follows ḍammah, so it is a true madd letter.
In «النَّاسُ», the article lām assimilates into nūn; the doubled nūn has ghunnah.
Practice:
يَوْمَ — soft līn, not automatically a two-count madd.
يَكُونُ — regular natural madd.
النَّاسُ — sun-letter assimilation plus ghunnah of the doubled nūn.
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Yawm, yakūnu, and an-nās
Al-Qāriʿah and Az-Zalzalah — Comparative Tajwīd Practice
In يَوْمَ, wāw is sākin after fatḥah, making it a letter of līn, not wāw madd. In «يَكُونُ», wāw follows ḍammah, so it is a true madd letter.
In «النَّاسُ», the article lām assimilates into nūn; the doubled nūn has ghunnah.
Practice:
يَوْمَ — soft līn, not automatically a two-count madd.
يَكُونُ — regular natural madd.
النَّاسُ — sun-letter assimilation plus ghunnah of the doubled nūn.