Toy designed for older audiences, such as teenagers or adults, demonstrate advanced concepts. Newton's cradle, a desk toy designed by Simon Prebble, demonstrates the conservation of momentum and energy. Not all toys are appropriate for all ages of children. Even some toys which are marketed for a specific age range can even harm the development of children in that range. "Age compression" is a toy industry term that describes the modern trend of children moving through play stages faster than they did in the past. Children have a desire to progress to more complex toys at a faster pace, girls in
Conservation of energy not escape the attention of Gottfried Wilhelm Leibniz. It was Leibniz during 1676–1689 who first attempted a mathematical formulation of the kind of energy which is connected with "motion" (kinetic energy). Using Huygens' work on collision, Leibniz noticed that in many mechanical systems (of several masses, "m" each with velocity "v"), was conserved so long as the masses did not interact. He called this quantity the "vis viva" or "living force" of the system. The principle represents an accurate statement of the approximate conservation of kinetic energy in situations where there is no friction. Many physicists at that time, such