Waves 2

Want to guess what type of wave this is? Then you need to know the four terms: wavelength, period, source, and depth of influence.

Want to guess what type of wave this is? Then you need to know the four terms: wavelength, period, source, and depth of influence.

Here’s the second in the lesson on waves. In this lesson we are focused entirely on 4 terms: period, wavelength, depth of influence, and source.


The period of a wave is the time it needs to complete one cycle.

If it takes less than a second, that is called a ripple.

From 1-10 seconds it is a chop.

From 10-30 seconds it is a swell.

From 5-90 minutes it is a tsunami wave.


Wavelength is the distance between two crests.

The most important thing to know is that a swell can have a wavelength of up to 100 meters. The smaller the wavelength, the closer to shore the wave is – usually.

Under 2 cm it is a ripple.

From 2cm – 10m it is a chop.

Up to 100 m it is a swell.

Anything larger than a swell falls into the tsunami category.

Depth of Influence

The depth of influence is how deep the wave influences the water underneath it. A wave with a large depth of influence will influence water much deeper than the wave. Ripples influence very little underneath them.

A ripple has a very shallow depth of influence.

A chop has a shallow depth of influence, less than half its wavelength.

A swell has a depth of influence that is roughly 1/2 of the wavelength.

A tsunami has a depth of influence that reaches to the bottom of the ocean floor.


All waves – except tsunamis – come from movement of the air above them, or something in the ocean. A tsunami is formed because of violent movement of the earth. These violent movements are things like landslides, volcanic eruptions, and earthquakes.

How we practiced these…..

So now that you know the definitions, how do you practice them?

We played a game to practice depth of influence. The depth of influence game goes like this:

1. I call out a type of wave.

2. The kids reach down to the floor, or close to it, depending on how far the depth of influence extends.

So when I said “tsunami,” the kids reached all the way to the floor.

Practicing wavelength and period

For these I simply drew a series of waves on paper and handed them to the kids. Each kid got a color. Nicholas first had to draw a line from one point to the next to represent period. Then Abby got to tell him if he was right. We switched roles with wavelength. Then we switched back. Then they got to tell me what lines to draw – and I purposefully drew them wrong to see if they would correct me.


Once again for the finale we went to the beach and got in the waves we were talking about. Nicholas decided that chops were the best for his boogie board because they “came quick enough, and had a short wavelength,” so he could get in a lot of waves. Abby decided she liked the ripples because they wouldn’t get her wet.

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