Learn about reaction time with this easy science project! All you need is a ruler! Have your child sit in a chair or stand with good upright posture, eyes looking across the room. Have them hold out their hand. Just above their hand, hold up a ruler (lowest number at the bottom) so that it hovers about 2cm above their fingers. Without warning, drop the ruler. The child must catch it as quickly as they can! Look at the number on the ruler found just above the child’s thumb. The lower the number, the faster the reaction time!