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When a greased iron needle is placed gen...

When a greased iron needle is placed gently on the surface of water at rest, it floats on the surface of water. Why?

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Due to surface tension, the free surface of water at rest behaves like a stretched membrane. When an iron needle does not prick the water surface the upward components of the force of surface tension acting on the iron needle balance its weight on a stretched membrane of water surface. Then the needle floats on the surface of water at rest.
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