Mechanical waves propagate through a medium, which is a substance that can be either a solid, liquid, or gas.

Here's why:

* Mechanical waves require a medium to travel: They are disturbances that travel by transferring energy from one particle of the medium to the next.

* Examples:

* Sound waves: Propagate through air, water, or solids.

* Water waves: Propagate through the surface of water.

* Seismic waves: Propagate through the Earth's crust.

Important note: Electromagnetic waves, like light, do not need a medium to travel. They can propagate through a vacuum.