The coin floats on top of the water due to a combination of the effects of surface tension and the weight of the coin relative to the surface of the water.
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Surface Tension: Water molecules are attracted to each other due to cohesive forces. This causes the surface of the water to behave like a stretched elastic membrane, creating surface tension. When the coin is placed on the water, surface tension provides an upward force that can support the weight of the coin.
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Weight of the Coin: The coin has a certain weight due to gravity, which would normally cause it to sink. However, if the weight of the coin is less than or equal to the force exerted by the surface tension (and doesn't break through the surface), it can remain afloat.
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Shape and Distribution: The flat shape of the coin also contributes to its ability to float. A wider area means that the force from the surface tension can distribute more evenly, creating adequate support for the coin’s weight.
In summary, the combination of surface tension creating an upward force and the weight of the coin being appropriately countered allows the coin to float on the surface of the water. If the coin were denser or if it were to disturb the surface tension too much, it may sink.
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