long Vowels Letters “Maddah Letters”
Madd means to stretch, to pull, The Maddah Letters (long Vowels Letters) will be prolonged for the duration of one Alif or two Harakah and the duration of one Alif /two Harakah is two seconds. There are three letters of Maddah. These are: alif (ا), yāʼ(ي) or wāw(و) The rule has the following conditions: 1.Alif Maddah: when Alif is silent and the letter before Alif has a Fatha () on it,then the letter Alif is called Alif Maddah and will be prolonged / stretched for two measures of Harakah (for two seconds) “”in short way: If there is fathah before alif letter then the Alif is called alif-maddah, will be pull equal to two harakah or one Alif ( duration of alif or two Harakah is two seconds) 2.wāw Maddah: when wāw has a Jazm/Sakoon and the letter before wāw has a Dammah on it, then this wāw is called wāw Maddah and will be prolonged for two measures of Harakah (for two seconds). “”in short: If there is Dammah before wāw Sakin then the wāw is called wāw-maddah, will be pull equal to two harakah or one Alif ( duration of alif / two Harakah is two seconds) 3.Ya Maddah: when yā has a Jazm/Sakoon and the letter before yā has a Kasra on it, then this yā is called yā Maddah and will be prolonged for two measures of Harakah (for two seconds). “”in short: If there is Kasrah before yā Sakin then the wāw is called wāw-maddah, will be pull equal to two harakah or one Alif ( duration of alif / two Harakah is two seconds) 
(Note) in some Arabic Scripts,the Maddah rule has the following conditions: The letters of madd must all be silent, have no diacritic ( Fatha , Kasrah, Dammah, Sakoon/Jazm) on them . 1.Alif Maddah: there must be Fatha on the letter before a silent alif. 2. Waw Maddah: there must be Dammah on the letter before a silent waw. 3.Ya Maddah: there must be kasrah on the letter before a silent yaa. silent means no Fatha,Kasrah,Dammah,also no Jazm, important: mostly this Script is used in the books which are printed in Arabian countries, also in the Quran which is printed in Arab specially for natives, you will not see in Arab printed Quran a sakoon/Jazm on these three letters if they are in the state of madd.) Example: 
Standing Fatha: Standing Fatha is also equal to Alif Maddah and will be prolonged like Alif Maddah. Standing Dammah: Standing Dammah is also equal to Waw Maddah and will be prolonged like Waw Maddah. Standing Kasrah: Standing Kasrah is also equal to Ya Maddah and will be prolonged like Ya Maddah. 
Silent Letter A letter which is free from any Harkat and Sukoon is called a silent letter. This letter will be written but not read. (Note) in Arab printed books Silent letters will prolonged when they are in the state of madd.
Sukoon This is a small circumflex or a small comma or circle-shaped diacritic, which is placed above a letter to indicate “absence” of sound i.e. that letter doesn’t make a sound at all! The letter before it and after it will make a sound but not the letter , which has a Sukoon is placed on it example: جْ 
