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
John David Jackson (physicist) various observable decay correlations in allowed nuclear beta decay involving the electron's momentum, its spin, the neutrino's momentum, and the nuclear spin that provide information about parity conservation or non-conservation and time reversal conservation or not. He also published an early paper on the then recently discovered muon-catalyzed fusion of hydrogen isotopes. While at the University of Illinois (1957–1967) Jackson initially continued work on weak interactions as well as strange particle interactions at low energy with Wyld and others. On sabbatical leave at CERN in 1963–64, he collaborated with Kurt Gottfried on production and decay of unstable resonances in high-energy