Crying and sobbing are not synonyms. They are both modified respiratory movements, but opposites.
Crying is an inspiration followed by many short convulsive expirations.
Sobbing is a series of brief, spasmodic inspirations followed by a prolonged expiration.
I'll admit I can't think of any practical application of this knowledge to either medicine or parenting. Although the next time someone bursts into tears in your presence, and you're desperately casting about for something, anything to do - you could try to determine which of the above definitions applies. But maybe keep your conclusions to yourself.