Yes, I think you have misunderstood the concept of "momentary verbs". These describe actions that are very short and often repeated several times in rapid succession. Examples of momentary verbs are : hit, jump, knock. The verbs in your examples are a different category of active verb, sometimes referred to as "transitional event verbs". They describe the beginning of an event or situation. Other verbs in this category are: arrive, start, lose. By the way, please don't think that terms such as "transitional event verbs" essential for learning English. You can manage to speak English perfectly well without ever having learnt to distinguish between a stative and dynamic verb. As native speakers, we instinctively know what form of a verb to use because we've been listening to and using English all our lives. Most native English speakers don't even know what a verb is, let alone a momentary verb! Remember that these are simply technical terms invented to describe and teach people ABOUT the language, and very few English-speaking people other than professional linguists would be aware of these distinctions. Chinese teachers seem particularly keen on emphasising these categories, and I'm not convinced about how useful that is. SHL... I added that last part to save you the trouble of telling us that you've been speaking English all your life and haven't a clue what "transitional event verbs" are. ;). Don't worry... you're not alone!

In general, using a continuous tense serves to 'add time' to what you are describing. If that is what you want to emphasise, then you use continuous tenses, if you don't, you can use a simple tense. In those cases you gave: (1) seems a bit odd, as a train departing really is a momentary thing. (2) Sounds as if the person is walking, so the passing sounds longer. I would not use that sentence to ask someone that was driving. Do you see how using a certain tense can imply extra information? (3) Although they use the verb 'join', the actual meaning is 'attending'. I think that 'join' is used to sound more friendly. But, as they are referring to the whole class, a continuous tense is appropriate. Sometimes people use an inappropriate tense. There's a certain European country whose speakers tend to overuse continuous tenses in English. I'm not sure if that is a hangover from how they use them, or an error in the collective understanding. That one thing alone acts as a marker of what is otherwise usually impeccable English. As a native speaker, it can sound a little odd, but to others it would go unnoticed.

Great observation. We can and do commonly use many verbs in both the present continuous and the future continuous to talk about the future. I will be studying all night so I can't go to the movies with you. = I am studying all night... Will you be reading this magazine later, or can I borrow it? = Are you reading this magazine later or can I borrow it? I am available for English lessons! Leah will be working until 7pm, so let's all meet a little later. = Leah's working until 7 so let's all meet later.

Please answer my question, or give some coments. Thank you!