Physics
Materials for rain-proof coats and tents owe their water-proof properties to

viscosity
surface tension
specific gravity
elasticity

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Physics
Railway tracks are banked on curves

to avoid frictional force between the tracks and wheels
the train may not fly off in the opposite direction
necessary centrifugal force may be obtained from the horizontal component weight of the train
necessary centripetal force may be obtained from the horizontal component of the weight of the train

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