Waves Transporting Energy

Particle movement can be understood as matter moving from A to Bae to bee. Imagine a car driving along a road or a football passing between players. There is a transfer of material from place to place. Waves are different. When they move they carry energy with them, and we refer to this movement as propagation.

Think of a wave traveling around the audience in a football stadium. Each person stands then sits down again, one after the other, creating a ripple effect that moves around the audience. The individuals don’t move from their seats, yet we can see the wave moving all the way around the stadium. So what is actually happening? As each individual stands and sits they exert a burst of energy, and trigger the next person to do the same. This way the wave transports energy around the stadium, moving from person to person. Scientists call the stuff a wave travels through the medium and in this case, it is the audience.

On the left, a spectator is shown repeatedly raising and lowering at their seat. A red arrow is used to show the repeated up-and-down vertical motion. 
In the top-right, several spectators, in various stages of this motion, form a wave pulse with a peak that propagates to the right. This wave pulse is drawn with a blue line and its peak corresponds with the spectator standing at their tallest. 
Below, comparison is made to a wave with a sine curve shape, drawn in blue, where individual particles oscillate up-and-down, forming peaks and troughs that propagate to the right. The oscillation of a single particle is shown with a red arrow.

Figure 1: Illustration of a human wave.

As a wave propagates through space, the particles in the medium oscillate about their undisturbed positions. We call this undisturbed position the equilibrium point. For waves rippling on a pond, the medium is the water. For sound waves coming from a guitar, the medium is the air. The visible light that we see with our eyes is actually an example of an electromagnetic wave. Electromagnetic waves are special. They do not need a medium and can travel through completely empty space by oscillating electric and magnetic fields. This is why the light from the Sun can reach us through the vacuum of space.