# Wave Speed

The speed of a wave is very similar to the speed of a particle. For particles, we track the movement of material, but for waves, we track the movement of energy. In progressive waves, we see this as the propagation of peaks and troughs. For a standing wave, no energy is transferred, peaks and troughs do not propagate and so they have zero speed.

The image below shows part of a wave propagating at 1 m/s.

Figure 1: Displacement-position graph for a wave pulse at three different times.

The speed, v, of the wave can be related to the frequency, f, and wavelength, λ, through the expression: v = . It can also depend on the medium the wave is traveling through. For example, sound waves traveling through the air have a wave speed of 343 m/s, while light waves which propagate through oscillating electric and magnetic fields travel at around 300,000,000 m/s in a vacuum. This is why when lightning strikes, we see the lightning bolt before we hear the thunder clap!The speed of the wave can be related to the frequency and wavelength through the expression: speed equals frequency times wavelength. It can also depend on the medium the wave is traveling through. For example, sound waves traveling through the air have a wave speed of 343 m/s, while light waves which propagate through oscillating electric and magnetic fields travel at around 300,000,000 m/s in a vacuum. This is why when lightning strikes, we see the lightning bolt before we hear the thunder clap!