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 understood at the time. This led to the dispute among later researchers as to which of these conserved quantities was the more fundamental. In his Horologium Oscillatorium, he gave a much clearer statement regarding the height of ascent of a moving body, and connected this idea with the impossibility of a perpetual motion. Huygens' study of the dynamics of pendulum motion was based on a single principle: that the center of gravity of a heavy object cannot lift itself. The fact that kinetic energy is scalar, unlike linear momentum which is a vector, and hence easier to work with did