Why is rāʾ heavy in الْأَرْضُ?

Al-Qāriʿah and Az-Zalzalah — Comparative Tajwīd Practice

• Rāʾ has kasrah
• Rāʾ is sākin after fatḥah
• Tanwīn follows rāʾ
• Rāʾ has qalqalah