***NOT A TEACHER***Star39, good afternoon. There are many spelling rules that you can find in a good book. The best way is to read a lot and then your eyes will tell you how to spell the word. Why do you double the "p" in "stop"? (a) "-ed" starts with a vowel. (b) "stop" has one syllable. (c) "stop" ends in one consonant. (d) There is one vowel iin front of the one consonant. (e) Therefore, you must double the last letter: stopP + ed. This also explains why you write "stopP + ing." (As you can see, "jump" does not meet these requirements. ) Thank you.
I think this is just one of those things that you have to learn by memorizing it. Like the genders of nouns in French, German, and I am sure other languages. Some things don't make sense, but, that's life!
I am not a teacher, however. Perhaps one can give you and me a reason for it.