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  3. Physics
  4. Assertion: A needle placed carefully on the surface of water may float, whereas the ball of the same material will always sink. Reason: The buoyancy of an object depends both on the materials and shape of the object.

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Q. Assertion : A needle placed carefully on the surface of water may float, whereas the ball of the same material will always sink.
Reason : The buoyancy of an object depends both on the materials and shape of the object.

AIIMSAIIMS 2017Mechanical Properties of Fluids

Solution:

When a needle is placed carefully on the surface of water, it floats on the surface of water due to the surface tension of water, which does not allow the needle to sink. In case of a steel ball, the surface tension of the water is not sufficient to keep it floating, so it sinks down.