Physics
A cyclist leans inwards when he is negotiating a curve so that

His weight may be reduced
No frictional force may be produced between the wheels and the axle
He may increase his speed
Necessary centripetal force may be available from the horizontal component of the normal reaction due to the track to maintain the curved motion.

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Physics
Lightning is produced when

Water vapour produces electricity in the clouds
Similar charges of electricity rush towards each other and then get repelled
Clouds strike against impurities in air and the friction burns up these impurities
Strong opposite charges in different clouds break down the resistance offered by the intervening air

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