In Piagetian psychology, conservation is the ability for a child to keep in mind what aspects of an object stay the same and what aspects of an object change when an object undergoes a physical change. For example, a child is shown two beakers which are identical in size to one another and which contain equal amounts of a blue liquid. The contents of one of the beakers would then be poured into a third beaker of different physical dimensions, but which could contain the same volume of liquid as the previous beaker. In other words, the new beaker would have a smaller diameter but a greater length, thus conserving volume. The child, when watching this occur, would then be asked whether this beaker contained an equal, greater, or lesser amount of liquid as the other beaker. A child with the inability to use conservation would answer that there is more water in the tall thin glass, because he or she would be unable to understand the notion of reversibility. Conservation normally develops between the ages of 7 and 12.