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A Little Wave Action

© Linda Bond

What's in a Medium?

Okay, so let's say you're sitting by a birdbath and you notice a leaf that falls into the water, which causes little ripples on the water's surface. The ripples are bigger when the leaf first hits, then get smaller quickly as they move away towards the edge of the birdbath. Or, perhaps you're sitting by a lake when all of a sudden a huge asteroid lands in the middle of the lake, and throws all of the water out at once....maybe we better stick with the birdbath!

So what happened? When the leaf hit the water, it transferred energy to the water which was the medium through which the ripples (or waves) traveled. This type of wave is called a mechanical wave. (We'll get to electromagnetic waves another time.)

When energy is carried through mediums like water, air or solids (examples of mediums), it is carried in a mechanical wave that has made the particles in the medium vibrate. When the wave in water is fresh, more energy is being carried and the ripple peaks are higher. As energy is dissipated, the peaks become shorter and shorter until the water becomes still again. Although the particles were set to vibrating, they return to their original position once the wave has passed.

When an earthquake occurs, mechanical waves are carrying energy through the ground. The larger the earthquake, the greater is the energy being carried and the greater is the damage to the surface (of course, the depth of the quake is also important). And when thunder follows a lightening strike, we actually hear it roll across the skies above us in a wave pattern.

What's Your Wave Type?

There are two types of waves caused by the vibration of particles in the medium being affected. First, the waves we see in water (as discussed above) are called transverse waves, in which water particles are vibrating at right angles to the direction in which the wave is traveling. As an example, if the wave is traveling from left to right in our vision, across the top of the water, the particles are vibrating up and down.

Longitudinal waves (sound waves are an example) are experienced when the particles in the medium vibrate back and forth in the same direction as the wave is traveling.

Who's Counting?

Those transverse waves we saw in the water were creating peaks (the high point of each wave section) and troughs (the low point). A wave cycle has one peak point and one trough. If you could count the number of wave cycles -- complete waves -- that pass a given point in just one second, you could know the frequency of the wave. A famous German scientist named Heinrich Hertz who lived in the 1800s was the first person to discover radio waves, and he is honored with having this measurement named after him. Thus, frequency is measured in hertz (Hz).