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6. When the cutting edge of a knife is put against a fast rotating stone to sharpen it, sparks are seen. Why?

7. We have two identical metal sheets. One of them is rubbed with sand paper and the other with ordinary paper. Which metal sheet will shine more and why?

Dear Student,
 
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.


Out of the two identical metal sheets the one rubbed with sand paper will shine more. Sand paper will remove the oxide layer and other deposits formed over the metal sheet and fresh metallic layer will be exposed due to rubbing which will lead to more shining.

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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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Answer 6 : Due to the friction between cutting edge of a knife and stone , the temperature of the knife and hence stone increases and it increases to such a level that the sparks are produced which can be seen while sharpening it.

Answer 7 : While rubbing with sandpaper , more frictional force is produced between the layers of metal sheet and sandpaper which causes more force on dust particles and they are removed easily , so it will shine more. But in case of an ordinary paper , the force of friction is not sufficient to remove all the dust , so it will shine less in the case.

Hope it helps :)
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Answer 6 : Due to the friction between cutting edge of a knife and stone , the temperature of the knife and hence stone increases and it increases to such a level that the sparks are produced which can be seen while sharpening it. Answer 7 : While rubbing with sandpaper , more frictional force is produced between the layers of metal sheet and sandpaper which causes more force on dust particles and they are removed easily , so it will shine more. But in case of an ordinary paper , the force of friction is not sufficient to remove all the dust , so it will shine less in the case.
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