Here's why:

* Mechanical waves are disturbances that travel through a medium. They are created by the vibration of particles within the medium.

* These particles transfer energy to their neighbors, causing the disturbance to propagate.

* Without a medium, there are no particles to vibrate and transfer energy. Therefore, mechanical waves cannot travel through a vacuum.

Examples of media:

* Solid: Sound waves traveling through a metal bar

* Liquid: Water waves in a lake

* Gas: Sound waves traveling through air

Examples of waves that don't need a medium (electromagnetic waves):

* Light

* Radio waves

* Microwaves

Let me know if you'd like more detail on any of these topics!