In an experiment with identical sound generators, which friend hears the sound first if one is underwater, one on wood, and one in air?

Sound travels through different mediums (solids, liquids, and gases) at varying speeds due to their physical properties. In this scenario, one friend is underwater, one is on wood, and one is in the air.

Sound travels fastest in solids because the molecules are packed closely together, allowing the sound waves to transmit quickly. Wood, being a solid, would facilitate faster sound transmission compared to air. Water, while a liquid, has a higher sound speed than air but lower than that of solid wood.

Therefore, the friend on wood hears the sound first, because sound travels through wood more rapidly than it does through water or air. The friend underwater will hear it after the one on wood, while the friend in air, where sound travels slowest, will hear it last. This explains why the correct answer is the friend on wood.