I have a question that really confuses me for several days. What is the difference between "on" and "about"?
For examples,
Professor Smith talks about Physics.
Professor Smith talks on Physics.

What is the difference between them?

Thank you!
To talk about something is to chat about it, to have a conversation about it in an informal setting.

To talk on something is to give a fairly formal talk on the topic with the intent to instruct, inform, or educate.
Thank you very much for your answer!