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3. Physical period: Uniform circular motion is a kind of periodic motion. The so-called periodicity refers to the fact that after a certain period of time, the moving object repeats back to its original position, and the instantaneous speed repeats back to its original size and direction. The time it takes for an object to move in a uniform circle is called a period. The period is expressed by the symbol T, and the period is also a physical quantity describing the speed of uniform circular motion. The long period indicates the slow motion of the object, while the short period indicates the fast motion of the object.这是一个远古时代恐龙家族如何生存的故事，其间反映了恐龙间的亲情和友情，并通过森林中的历险再现了它们的勇敢和诚实精神，此片给我们展现了一幅远古时期生物的进化图卷。再不就吃嘴唇吧，那块肉最软。Liz Bonnin presents a controversial and provocative episode of Horizon, investigating how new scientific research is raising hard questions about zoos - the film explores how and why zoos keep animals, and whether they need to change to keep up with modern science or ultimately be consigned to history.Should zoos cull their animals to manage populations? Liz travels to Copenhagen Zoo, who killed a giraffe and fed it to the lions, to witness their culling process first hand. They think it is a natural part of zoo keeping that is often swept under the carpet. Should some animals never be kept in captivity? In a world exclusive, Liz visits SeaWorld in Florida and asks if captivity drove one of their orcas to kill his trainer.But could zoos be the answer to conserving endangered species? Liz examines their record, from helping breed pandas for the wild to efforts to save the rhinos. She meets one of the last surviving northern white rhinos and discovers the future of this species now lies in a multimillion-dollar programme to engineer them from stem cells. Veteran conservation scientist Dr Sarah Bexell tells Liz the science of captive breeding is giving humanity false hope.Trump spoke to reporters after the "King's Meeting 2.0" was not discussed. After answering questions from a few US and international reporters, Trump chose a reporter from the Russian satellite network.弗朗机贼人以天主之名，行淫掠之事，只求船主替天行道，扬我国威。