Why does an iron needle float on clean water but sink when some detergent is added to this water?

Explanation

To understand why an iron needle floats on clean water but sinks when detergent is added, we can break down the explanation into several steps:

### Step 1: Understanding Surface Tension
- Surface tension is a property of liquids that causes the surface to behave like a stretched elastic membrane. It results from the cohesive forces between liquid molecules.

### Step 2: The Iron Needle on Clean Water
- When an iron needle is placed on the surface of clean water, it floats due to the surface tension of the water. The cohesive forces between water molecules create a "membrane" effect on the surface, which can support the weight of the needle.

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