Out of the given options, the pair of substances that would float in a tumbler half filled with water is feather and plastic ball.
- Feather and plastic ball are both less dense than water. This means their mass is distributed over a larger volume compared to water. Consequently, the buoyant force exerted by the water upwards is greater than the gravitational force pulling them downwards, allowing them to stay afloat.
- Cotton thread, while initially appearing to float, will eventually become saturated with water and sink. Water molecules can easily infiltrate the tiny spaces between the cotton fibers, increasing its weight and density beyond that of water.
- Pin and coin are both denser than water. Their weight overcomes the buoyant force, causing them to sink.
- Oil drops are a special case. Oil and water don’t mix, so oil drops would form distinct globules on the water surface without actually sinking. However, they wouldn’t be considered truly “floating” in the same way as the feather and plastic ball, which are integrated with the water body.
Therefore, considering the principle of buoyancy and density, feather and plastic ball are the clear winners for floating in a tumbler half filled with water.
I hope this complete explanation helps! Let me know if you have any other questions.