Rule 1: 1. Form I: the و disappears in the imperfect and the imperative
In the imperfect active of Form I the initial و drops out altogether and the second radical takes i: وَصَلَ gives يَصِلُ he arrives, وَعَدَ gives يَعِدُ he promises, وَجَدَ gives يَجِدُ he finds, وَقَفَ gives يَقِفُ he stops, وَزَنَ gives يَزِنُ he weighs. The imperative is made from the jussive as usual, but since cutting off the prefix of تَصِلْ leaves صِلْ, which already begins with a vowelled letter, no hamzat al-waṣl is needed: صِلْ arrive!, عِدْ promise!, جِدْ find!, قِفْ stop!, زِنْ weigh!
يَصِلُ الْقِطَارُ إِلَى الْمَحَطَّةِ فِي السَّاعَةِ السَّابِعَةِ.
yaṣilu l-qiṭāru ila l-maḥaṭṭati fi s-sāʿati s-sābiʿati
The train arrives at the station at seven o'clock.
أَعِدُكَ أَنْ أَتَّصِلَ بِكَ عِنْدَ وُصُولِي.
aʿiduka an attaṣila bika ʿinda wuṣūlī
I promise you that I shall contact you on my arrival.
أَعِدُ: first person of يَعِدُ; the و of the root has gone.
لَمْ نَجِدْ حَقَائِبَنَا عَلَى الرَّصِيفِ.
lam najid ḥaqāʾibanā ʿala r-raṣīfi
We did not find our bags on the platform.
Jussive of يَجِدُ after لَمْ.
قِفْ هُنَا وَلَا تَقِفْ أَمَامَ الْبَابِ.
qif hunā wa-lā taqif amāma l-bābi
Stop here and do not stop in front of the door.
Imperative قِفْ, prohibition لَا تَقِفْ; both lack the و.
زِنِي الْحَقِيبَةَ قَبْلَ أَنْ تَصْعَدِي إِلَى الطَّائِرَةِ.
zini l-ḥaqībata qabla an taṣʿadī ila ṭ-ṭāʾirati
Weigh (f.) the suitcase before you board the plane.
Feminine imperative زِنِي, two letters and an ending; its final ī is shortened before the article.
عِدُونِي أَنْ تَصِلُوا قَبْلَ الْمَغْرِبِ.
ʿidūnī an taṣilū qabla l-maghribi
Promise (pl.) me that you will arrive before sunset.