A Partnership of the National Science Foundation and Time for Kids. Trace and cut out three circles. Circle one should be three inches in diameter. Circle two should be six inches in diameter. Circle three should be nine inches in diameter.
Tape circles two and three to the wall.
Hold circle one as far from you as you can. Close one eye. Move away from the wall until circle one is the same size as circle two. Have your partner measure the distance. Do the same thing for circle three.