Why does the 'A' in the word "cat" sound different to 'A' in the word "car"?
If I want the 'A' in a foreign name like 'Pardis' to sound like the 'A' in cat, how should I write it?
Why does the 'A' in the word "cat" sound different to 'A' in the word "car"?
If I want the 'A' in a foreign name like 'Pardis' to sound like the 'A' in cat, how should I write it?
I don't think there is a short-cut to this, what I know is that you have to use these vowels everyday, as often as you can. I know because I've been there, at first it might be confusing, but as you go you will remember the pronunciations by heart.
You might want to start conversing with native-speakers, or at least watch English movies, music, speech, etc. to help you with your pronunciations.
Here is a link about the pronunciations to get you started: http://en.wiktionary.org/wiki/Appendix%3AEnglish_pronunciation
There are two questions here. The first—“Why does the 'A' in the word "cat" sound different to 'A' in the word "car"?”—has a simple answer. They sound different because they are different vowels. John Lawler’s explanatory comment is correct—English has more vowel sounds than vowel letters, so some letters have to do double (and triple) duty. In this case, the letter 'a' represents both the sound /æ/ as in “cat” and the sound /ɑ/ as in “car” (or “spa”).
As for the second question—how would you represent the spelling of a word that is supposed to have the vowel of “cat” followed by an “r” and “d” sound, Peter Shor is correct in his comment on the original question: the /æ/ sound as in "cat" is not possible before a sequence of /rd/ in English. No English words have the sequence /ærd/, so no spelling would ever elicit such a pronunciation. If you explain how to pronounce it, native English speakers could combine the sounds as described, but it does not sound like English.
But why? First of all, such a pronunciation would only be possible in a rhotic dialect of English. In non-rhotic dialects, non-prevocalic /r/ sounds (that is, an /r/ sound that does not come just before a vowel) are not pronounced. However, even in rhotic dialects, only some vowels can be combined with /r/ in the same syllable:
ɜr as in NURSE
ɑr as in START
ɔr as in NORTH
ɪr as in NEAR
ɛr as in SQUARE
ʊr as in CURE
ər as in LETTER
No other vowels can be combined with /r/ in the same syllable, including /æ/.