Physics
When a bottle of scent is kept open in a corner of a room its odour is felt in all parts of the room. This is due to the phenomenon of :

Vaporisation
Sublimation
Diffusion
Evaporation

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Physics
Railway tracks are banked on curves so that

Necessary centripetal force may be obtained from the horizontal component of the weight of the train
The train may not fall down inwards
No frictional force may be produced between the tracks and the wheels of the train
Necessary centrifugal force may be obtained from the horizontal component of the weight of the train

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