A wide open space (It could be your backyard or a park.) Two Hula-Hoops (Alternatively, you could use two flat rocks or bricks that you can sit on.) A yardstick or meterstick (Use one that has clear ...

Try this experiment: extend your thumb at arm’s length and close one eye at a time. Your thumb will seem to ‘jump’ between two positions as you switch the eye that is closed. That jump is known as ...