Did you know - Why not Do you know?

[Tom]

Hi

I have seen Did you know? at the top of some information as a heading. Why not Do you know?

Recently I was reading an article by an American author.

Did you know that black peppers win you energy? Which is why it is given in such abundance to...

Why not Do you know? Would it be wrong?

peppers=it??? shouldn't it be they?

Starting a new sentence with which. Correct???

[Alan]

Hi Tom,

Do you know? is a relevant question to what/how/when and so on pertaining to/relevant to asking for/seeking information as in:

Do you know when the train goes?
Do you know what that costs?
Do you know how much electricity you use?

Did you know? is much more probing and inquistive with the suggestion I do know and I believe you don't as in:

Did you know that debts have risen in the UK over the last 10 years?
Did you know that he is the son of a famous actor?
Did you know that he got more votes and yet he lost the elction?

Alan
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English as a Second Language
You can read my ESL story Present Simple

[Yankee]

Hi Tom

I'd say "Did you know (that ...)" is typically used when you are just about to state the information that is being asked about. I'd say it sounds nicer (and/or less like you think you're a know-it-all) than the more direct "Do you know (that ...)".

I can imagine using "Do you know (that ...)" in a more confrontational situation, for example. So, I wouldn't use it in a sentence like the one you quoted.