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
Tests of relativistic energy and momentum mass formula_10 equivalent to the "relativistic mass" formula_11 as indicated above). Since relativistic mass is not often used anymore in modern textbooks, those tests can be described of measurements of relativistic momentum or energy, because the following relation applies: Electrons traveling between 0.25–0.75c indicated an increase of momentum in agreement with the relativistic predictions, and were considered as clear confirmations of special relativity. However, it was later pointed out that although the experiments were in agreement with relativity, the precision wasn't sufficient to rule out competing models of the electron, such as the one of Max Abraham. Already in 1915,