Vaisesika Sūtra 1.1.29

गुरुत्वप्रयत्नसंयोगानामुत्क्षेपणम् ॥२९॥

gurutva-prayatna-saṁyogānām utkṣepaṇam ॥29॥

[गुरुत्व-प्रयत्न-सम्योगानाम् (gurutva-prayatna-saṁyogānām) - of heaviness, effort, and conjunction; उत्क्षेपणम् (utkṣepaṇam) - upward motion;]

By the striving of gravity, 'conjunction' comes about.