Sound travels slowest through a solid medium primarily because of its high density and the way particles interact with each other. In a solid, such as a metal or a dense material like granite, the atoms or molecules are closely packed together and have strong intermolecular forces.
When sound waves propagate through a medium, they transmit energy by causing particles to vibrate. In a solid, these vibrations are transmitted from one particle to another through a series of collisions. Due to the dense arrangement of particles and the strong intermolecular forces, these collisions between particles occur more frequently and take longer to propagate through the material. As a result, the speed of sound in a solid is slower compared to other states of matter like liquids or gases.
In addition, the stiffness or rigidity of a solid also contributes to the slower speed of sound. Solids tend to have a higher bulk modulus, which is a measure of their resistance to compression. This high stiffness causes the sound waves to travel more slowly through the solid medium.
It's worth noting that the actual speed of sound in a solid can vary depending on the specific material and its properties, such as density, elasticity, and temperature. Different solids have different speeds of sound, with some materials transmitting sound faster than others.