Physics
No current will flow between two charged bodies if they have the same

Resistance
Potential
Charge
Charge/ potential ratio

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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
The train may not fall down inwards
Necessary centripetal 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

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