Cosmos: A Sketch of the Physical Description of the Universe by Alexander von von Humboldt, Nicolaas A. Rupke

By Alexander von von Humboldt, Nicolaas A. Rupke

The first quantity of Cosmos, his five-volume survey of the universe, seemed in 1845, even though Humboldt had worked at the whole paintings for almost part a century. He scrupulously despatched sections of the paintings to different specialists for feedback and corrections. The final quantity, prepare from his notes after his demise, seemed in 1861. The volumes have been translated virtually as speedily as they seemed. This paperback variation reprints the Harper & Brothers variation, released in big apple in 1858-59.

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Extra resources for Cosmos: A Sketch of the Physical Description of the Universe (Foundations of Natural History) (Volume 1)

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37. 9 - la tensione T esercitata dalla fune; la reazione R esercitata dalla parete. 9. La puleggia differenziale `e una macchina costituita da: due pulegge connesse rigidamente con l’asse di rotazione fisso in comune, una puleggia mobile al cui asse viene appeso il corpo di peso P da sollevare, una fune avvolta come in Fig. 37 c attorno alle pulegge. Indichiamo con r e R i raggi delle due pulegge ad asse fisso. Si determini la forza T che `e necessario applicare al punto A della fune per tenere in equilibrio il corpo di peso P nei due casi: a) il peso della fune `e trascurabile; b) il peso della porzione di fune liberamente appesa (nella figura, il tratto ABC) `e p.

La forza con cui l’uomo grava sulla piattaforma `e pertanto P − F . 44) τi = 0 . 43), d` a: P = F + T1 + T2 ⇒ P = 4F ⇒ F = P/4 . 46) L’intensit` a di F `e cos`ı determinata. 44) `e necessaria ma non sufficiente per l’equilibrio. 45), cio`e la condizione sui momenti. Calcoliamo i momenti rispetto al punto O di appoggio dell’uomo sulla piattaforma: 2 R T2 = R T 1 ⇒ T1 = 2 T 2 . 43). 45) `e pertanto soddisfatta. ` possibile mantenere l’equilibrio nel caso le due carucole abbiano raggi B) E diversi ?

25 c,d). Sui due cilindri inferiori il cilindro superiore esercita le forze R12 e R13 . Per il principio di azione e reazione R12 = −R21 , R13 = −R31 . 32) assicura che R12 = R13 . Per determinare l’incognita R2 = R3 `e pertanto sufficiente considerare la condizione di equilibrio delle forze agenti su uno solo dei due cilindri inferiori, ad esempio il n◦ 2 (quello di sinistra) e proiettarla sull’asse x: √ R2 = | R12x | = | R21x | = P/2 3 . ) Perch´e nel diagramma di corpo libero del cilindro 2 non si `e considerata la reazione esercitata dal cilindro 3 (e viceversa) ?

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