(WVS) Types of Mechanical Waves: Transverse Waves Lesson

Types of Mechanical Waves

Transverse Waves

In a transverse wave, the vibration direction is perpendicular (at right angles) to the direction in which the wave travels or propagates. Transverse waves are very common - waves in water and on strings are two good examples.

A transverse wave can also be set up on a slinky spring - have a look at this animation:

It is important to know that a wave transports energy along a medium without transporting matter. As seen in the animation above, a wave was introduced into a slinky when the person holding the first coil gave it a back-and-forth motion. This creates a vibration within the medium; this vibration subsequently travels from coil to coil, transporting energy as it moves. The energy is transmitted to the medium by the person as the person does work upon the first coil to give it kinetic energy. This energy is transferred from coil to coil until it arrives at the end of the slinky. You would notice the energy being transferred if you were holding the opposite end of the slinky. This is why a high-energy ocean wave can do damage to the rocks and piers along the shoreline when it crashes upon it.

Not all waves are transverse, and we'll come back to the slinky in order to look at an important second wave type. Before we do that, have a look at another transverse example, showing a particle model of a transverse wave. These particles could be metal molecules in a solid vibrating plate, or water molecules showing ripples traveling across a pond.

Characteristics of a Transverse Wave

Waves have moving crests (or peaks) and troughs. A crest is the highest point the medium rises to and a trough is the lowest point the medium sinks to. Crests and troughs on a transverse wave are shown below:

The distance between the crest and the equilibrium position is equal to the distance between the trough and the equilibrium position. This distance is known as the amplitude of the wave, and is the characteristic height of the wave, above or below the equilibrium position.  The amplitude on a transverse wave is shown below:

The distance between two adjacent crests is the same no matter which two adjacent crests you choose. There is a fixed distance between the crests. Similarly, we have seen that there is a fixed distance between the troughs, no matter which two troughs you look at. More importantly, the distance between two adjacent crests is the same as the distance between two adjacent troughs. This distance is called the wavelength of the wave. The symbol for the wavelength is λ (the Greek letter lambda) and wavelength is measured in meters (m). The wavelength of a transverse wave is labeled below:

Imagine you are sitting next to a pond and you watch the waves going past you. First, one crest arrives, then a trough, and then another crest. Suppose you measure the time taken between one crest arriving and then the next. This time will be the same for any two successive crests passing you. We call this time the period, and it is measured in seconds.

Imagine the pond again. Just as a crest passes you, you start your stopwatch and count each crest going past. After 1 second you stop the clock and stop counting. The number of crests that you have counted in the 1 second is the frequency of the wave.   Frequency is measured in Hertz (Hz).

Frequency and period are related. Frequency is a measure of how often the wave occurs while period measures the time it takes for one wave to pass. Frequency and period have a reciprocal relationship.  The less time it takes for a wave to pass means that more waves can occur in a given amount of time.  

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