Learn Arabic (Modern Standard): يدحرج الولد العجلة ببطء.

يدحرج is a quadriliteral verb, meaning its root has four consonants (د-ح-ر-ج). Just like Forms II, III, and IV of regular verbs, the present tense prefix of a quadriliteral verb always takes a damma (yu-), and the second-to-last root letter takes a kasra (-ri-). It follows the pattern يُفَعْلِلُ.

How do you form the past tense of يدحرج?

The past tense is دحرج (dahraja). For basic four-consonant verbs, the past tense pattern is simply فَعْلَلَ (fa'lala). The first, third, and fourth root letters take a fatha, while the second takes a sukun.

Why is 'slowly' expressed as ببطء (bi-but')?

Arabic doesn't have an exact equivalent to the English '-ly' suffix for adverbs. A very common way to describe how an action is done is to use the preposition بـ (with) attached to a noun or verbal noun. Here, it is بـ attached to بطء (slowness), literally translating to 'with slowness'.

Why is the hamza in ببطء written sitting alone on the line rather than on a seat like waw or ya'?

When a hamza is the last letter of a word and comes immediately after a consonant with a sukun (meaning no vowel sound), it is written alone on the line. Since the letter Ta' in بطء has a sukun, the final hamza has no 'seat' and sits directly on the line.