Physics
A needle or a pin floats on the surface of water because of

Adhesive force
Viscosity
Surface tension
Surface energy

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Physics
Railway tracks are banked on curves

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

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