Physics
The sky appears blue because

It is actually blue
All colours interfere to produce blue
In white light, the blue component dominates
The atmosphere scatters blue colour more than the others

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Physics
Railway tracks are banked on curves so that

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

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