Here's why:

* Wave motion: Imagine dropping a pebble into a still pond. The ripples that spread out from the point of impact are the wave motion. The water particles themselves don't travel far; they oscillate up and down or back and forth.

* Energy movement: The energy from the pebble's impact is what travels outward. This energy is transferred from one water particle to the next, causing them to oscillate.

In summary:

* Wave motion: The movement of the medium (water, air, etc.) is perpendicular to the direction the energy travels.

* Energy movement: The direction of energy transfer is parallel to the direction the wave travels.

This is true for all types of waves, including:

* Transverse waves: Like water waves, where the motion of the medium is perpendicular to the direction of energy transfer.

* Longitudinal waves: Like sound waves, where the motion of the medium is parallel to the direction of energy transfer.