Sound is a form of energy that is produced by vibrating objects. It is created when these objects transfer their energy to the surrounding medium, causing it to vibrate. This vibration travels through the medium in the form of sound waves, which our ears can detect and interpret.

To understand how sound travels through different mediums, let's consider two common examples. First, in air, sound is transmitted as longitudinal waves. As an object vibrates, it creates regions of compression and rarefaction in the air particles. These regions of high and low pressure propagate through the air, ultimately reaching our ears.

In contrast, in solids like metal, sound waves travel as both longitudinal and transverse waves. The vibrating object creates compressions and rarefactions, similar to air, but the waves can also propagate through the solid's structural vibrations. This is why we can often hear sound more clearly through solid materials, such as when we listen to music through headphones.

By understanding the basics of how sound is defined and how it travels through different mediums, we can now delve deeper into its properties and the physics behind it.