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Nobody will try to stop the sails of a windmill with his hands, or the 50 metres long blades of a 2 MegaWatt wind turbine, but the small ventilator of your computer can easily be stopped although it has a much larger angular velocity than the windmill and the wind turbine. The quantity to reckon with is not the angular velocity, but the angular momentum which depends on three factors, namely the angular velocity, the mass and the extension of the object. The video shows first that the extension is an important factor for the value of the angular momentum. In order to keep the angular momentum at the same value (conservation of angular momentum), the angular velocity of a rotating person slows down when the person stretches his arms and vice versa. Conservation of angular momentum is furthermore demonstrated with the girl while standing on a freely rotating disk. When she changes the orientation of the angular momentum of the bicycle wheel, she starts rotating herself in order that total angular momentum remains unaltered. |