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
Stress–energy–momentum pseudotensor are inappropriate objects in general relativity, but the conservation law only requires the use of the 4-divergence of a pseudotensor which is, in this case, a tensor (which also vanishes). Also, most pseudotensors are sections of jet bundles, which are now recognized as perfectly valid objects in GR. The use of the Landau–Lifshitz pseudotensor, a stress–energy–momentum pseudotensor for combined matter (including photons and neutrinos) plus gravity, allows the energy–momentum conservation laws to be extended into general relativity. Subtraction of the matter stress–energy–momentum tensor from the combined pseudotensor results in the gravitational stress–energy–momentum pseudotensor. Landau and Lifshitz were led by four