Experiment with light and vision, sound, and hearing.
Our eyes and ears respond to light and sound waves, but these are just the first steps in perceiving the world. Playing with light and sound is the best way to learn how they work. Investigating real phenomena can also give you a deeper understanding of the scientific process.
Sand scattered on a large metal square vibrates and jumps in response to the sound of your voice. When you hit just the right note(s), the sand spontaneously migrates into elegant geometrical patterns.