Sat February 19, 2011 By: Arun Iyer

Why does a needle floats on water but sink when some impurities are added.

Expert Reply
Sun February 20, 2011
Dear student

The surface tension of clean water being higher than that of water mixed with impurities, it can support the weight of a needle due to its surface tension. By addition of impurity, the surface tension of water reduces, thereby resulting in the sinking of the needle.

Hope this clarifies your doubt.
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