Periscope and kaleidoscope

Light travels in straight lines and mirrors change its direction. Put those two facts together and you can build useful things.

A simple periscope is a Z-shaped box with two plane mirrors inside, one at each bend, both tilted the same way. Light from an object hits the top mirror, is reflected down the tube to the bottom mirror, and is reflected again into your eye. Two reflections let you see things that are not in your direct line of sight.

Periscopes are used in submarines, in tanks, and by soldiers to see out of their bunkers. You could use one to see over taller friends in a crowd.

A kaleidoscope is made differently. Take three rectangular mirror strips of the same width and join them into a triangle (thick reflective paper strips work too).

Fix the triangle inside a round tube of thick chart paper. At one end, fix a clear plastic sheet with a rubber band or tape. Put broken pieces of coloured bangles or beads on it, and cover them with tracing paper, fixed with a rubber band or tape.

Look in through the open end: you see a beautiful pattern. The three mirrors reflect the coloured pieces again and again, making a symmetrical design. Turn the tube and the pieces shift, and the pattern changes every time.