Needle on the surface of water (Urdu & English)
Using a cardboard or a fork as a carrier, place a needle on the surface of water in a dish. Carefully remove the carrier.
You will see that: The needle will float.
Explanation: The needle is heavier than the amount of water it displaces and should be expected to sink. It ~oats, however, because of an invisible elastic skin. When water comes in contact with air, the molecules on the surface of the water huddle closer together and form a thin film or skin over the surface. 2. Dip a piece of soap in your dish with the floating needle. You will see that: The needle sinks immediately.
Explanation: The soap reduces the surface tension. it is one of the reasons we use soap for cleaning. By lowering surface tension, soap makes water able to wet greasy surfaces.