Here's why:

* Mechanical waves require a medium to travel. This means they need a substance (like air, water, or a solid) to vibrate and transmit energy. Examples include sound waves and water waves.

* Electromagnetic waves are made up of oscillating electric and magnetic fields. These fields can exist and propagate even in a vacuum, meaning they don't need a medium to travel. Examples include light, radio waves, X-rays, and microwaves.

Let me know if you have any other questions!