Here's why:

* Mechanical waves require a medium to travel: Sound waves are a good example. They travel through air, water, or solids by causing particles in the medium to vibrate.

* Electromagnetic waves do not need a medium: UV waves, along with visible light, infrared, X-rays, and radio waves, are all examples of electromagnetic waves. These waves are disturbances in electric and magnetic fields that can travel through a vacuum (like space).

In summary: UV waves are a form of electromagnetic radiation, not a mechanical wave.