>A balloon floats in air if it is filled with helium, or any other gas less dense than air. Same applies to any other medium. Denser items sink. Where is gravity? Explain gravity without quoting a text book.
Explain your "question" first. Why does helium balloons make you question gravity, and how on Earth did this line of thinking lead you to believe the Earth is flat?
Condense your thoughts into a question that makes sense, and you will be provided with a sensible answer.