Phonetics and the IPA 7, Exercise 2: pearl and car

RP is non-rhotic: /r/ occurs only before a vowel. So the r of pearl and car
(before silence or a consonant) is not pronounced; the vowel carries the
information instead (car /kɑː/; pearl uses the NURSE vowel /ɜː/ with no r).

General American is rhotic: /r/ is pronounced in all spelled-r positions, as
in pearl, car and fort. So car is /kɑɹ/ and pearl uses an r-coloured vowel
(the source lists [ɚ] for NURSE).

Scottish English typically keeps the /r/ in the coda too, with some
non-rhotic varieties in Edinburgh and Glasgow.

So GA keeps the /r/ (and most Scottish speakers), RP drops it.