The words particle and wave are two words you’ll see in nearly every area of physics, but they are actually very different from each other. A particle is a tiny concentration of something that can transmit energy, and a wave is a broad distribution of energy that fills the space it passes through. We’re going to look at particles in more depth later, and instead focus on understanding waves.
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A wave traveling along a stretched string can have different shapes, but every wave will have a frequency and a wavelength. Wavelength refers to the repeating wave shape, and frequency refers to the oscillating source that make the wave in the first place. Waves are defined by a math equation that we’ll get to a little later. First, let’s take a look at the different parts of a wave.

A wave number is the number of waves per unit length.

For longitudinal waves, a rarefaction is the spot where the the wave is traveling and is the most “stretched out” (minimum wave density). The compression is the spot where the wave is most squished together. You can see this easily if you play with a slinky… the coils that are most spread out are a rarefaction point.

Click here to go to next lesson on Period, Frequency, Amplitude and Wavelength.

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