Scientists are interested in the relationships between the things they study. If they study birds, they are interested in the relationship between a birds physical characteristics and the type of food they eat. They are interested in the type of nests that each bird makes in relation to the places that they live; sea birds, shore birds, forest birds, meadow birds. If they are studying the body and health they will want to find the relationship between what we eat and how we feel. They will want to know the relationship between daily exercise and how long we can live. If they study the planets they will want to know the relationship between comets and dents on the surface of the moon and Mars.