Activities using Humidity Measurements
There are a number of activities you can experiment with to find out more about humidity.

Contrast the relative humidity measured first thing in the morning, with that at midday and mid afternoon. Why does this change on days when there is no change in the weather? e.g. on a clear, fine day.

Using Seaweed
Next time you go to the beach, bring back a piece of sea weed or algae. Leave it where you can check it everyday, preferably outside. Why does it change from brittle to flabby?