Air is around us even when we cannot see it. Air takes up space. Moving air can push a light paper strip.
Worked example
With an adult, gently move a large sheet of paper like a fan, away from faces. A paper strip on a clear table may move. The moving air gives us a clue.
A cup outline contains enlarged model dots representing air particles. The dots are not dust or actual particle sizes; air takes up space even when it cannot be seen.
