Answers

2015-06-11T20:04:51+05:30
The reason of sparks is friction.between the knife and rotatory stone.
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2015-06-11T23:00:37+05:30
Due to friction between knife and the rotating stone, the edge of metal knife becomes very hot. And small particles of the knife tear away from the hot edge. Due to excessive heat, the small particles glow which are seen as spark.
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