what's the difference between 慢慢 and 渐渐？
For example why can you use 慢慢 here，but not 渐渐？ ex） 你慢慢吃吧，别着急！
So, it's a habit.
Sometimes, 慢慢＝漸漸, for example,
We have the habit to say 你慢慢吃吧.
We don't have the habit to say 你漸漸吃吧.
I am talking about the Chinese, not the English.
For people who understand the difference between slowly and gradually, there shouldn't be any problem for them to tell the difference between 慢慢(slowly) and 漸漸(gradually)
慢慢(slowly) is an adverb that describes an action progress in a slow and continuous speed; 漸漸(gradually) is an adverb that describes something progress/change in tiny, almost undetectable increments.
烏雲慢慢散去 means the cloud dissipate in a very slow motion
烏雲漸漸散去 means the cloud dissipates in a very slow motion or dissipates little by little.
慢慢 can modify both action verbs like "speak", "eat" and "walk"; and non-action verbs like "think", "finish" and "understand"
漸漸 mostly modify non-action verbs
Saying 漸漸吃(gradually eat) doesn't make sense, but 漸漸吃完 (gradually finish eating) does.
你多看一些例子，漸漸就會懂了 = see more examples, you will gradually (little by little) understand.
你多看一些例子，慢慢就會懂了 = see more examples, you will slowly(after a long time) understand.
Because 慢慢 has several meaning depends on context.
慢慢来， 罗马不是一天建成的。 Dont' rush , Rome wasn't built in a day. Slow down, Rome wasn't built in a day
你慢慢吃吧，别着急! Eat slowly, there is nothing to worry about.
慢慢来， 我们餐厅十点才打烊。 No hurry, our restaurant close at 10pmSlow down,
慢慢教，他才六岁而已 Don't rush, he is just 6 year's old