CLEAN : Migrants head for Croatia to avoid Hungarian fence

The video tutorial introduces the concept of vacuum and concludes with a thank you note.

What is the main topic introduced in the first section of the transcript?

• The concept of vacuum

• The concept of density

• The concept of gravity

• The concept of pressure

What does the speaker express in the second section?

• A request for feedback

• A statement of confusion

• A call to action

• Gratitude and thanks