Lesson Background and Concepts for Teachers
A wave is a change (a variation) that travels through a substance (or medium). You can often see the change, such as the increased height of a traveling ocean, but what is important to understand is that the medium itself does not travel with the wave.
Ripples in a pond are good examples of waves. If no wind, a pond is smooth until a rock is thrown in and disturbs the water. Then ripples, "disturbances" in the pond, travel to the edges. The medium in this case is the water, through which the ripples travel. The water is not actually moving, but the waves (ripples) are.
Waves move in two ways: longitudinally and transversely. Transverse waves oscillate (move back and forth) in a direction perpendicular to their motion. Our pond ripples, for instance, oscillate up and down but move horizontally towards the edge of the pond. Because the ripples oscillate perpendicular to their horizontal motion towards the edge, they can be classified as transverse waves.
An electromagnetic wave is a transverse wave that can travel through empty space or a vacuum. Literally, electromagnetic waves are able to travel through "emptiness," unlike sound waves, which need "something" to travel through (for example, water or air). Electromagnetic waves have two parts to them: electric and magnetic. Both of these parts are considered transverse waves.