There are two types of wave motion: transverse and longitudinal. You need to learn these names, and what distinguishes them.

Transverse is the one most people can draw. The oscillations are at 90° to the wave motion: transverse wave

One way of remembering this is that is looks like an s on its side. Transverse has two s's in, longitudinal has none. Most waves are transverse, only a few are longitudinal. Here is a list of transverse waves that you might meet:

* all electromagnetic waves
i.e. radio, micro, infra red, light, ultra violet, X-rays and gamma waves
* water waves - ripples on the surface of a sea or lake
* S Waves - a type of earthquake wave Here the oscillations are in the direction of wave motion.

animation of longitudinal wave motion

For this type, and transverse, no matter moves anywhere overall. The oscillations are around a central position - sometimes called the equilibrium position.

Examples of longitudinal waves are sound, ultrasound and earthquake P-waves.Perhaps the simplest definition in waves is the wavelength. It doesn't take a genius to realise that this is the length of the wave :-)

The biggest mistake most people make is with drawing this on a picture of a transverse wave. Draw a complete wave length - from the same point on each wave ripple: wavelength of a transverse wave

Notice that the correctly drawn wavelength starts and finishes at parts of the wave that are doing the same thing.
As with transverse waves, wavelength is the distance between parts of the wave that are doing the same thing. All waves involve an oscillation of some kind. This means that something is pulled away from an equilibrium position, moves back, then through the other side.

We call the amount of movement from equilibrium displacement. Amplitude is just the Amplitude is defined as the maximum displacement from the rest position. In other words, the furthest distance something moves from where it was at rest.

Looking at the snapshot below of part of a longitudinal motion. At the top, the red line is at its rest position.

amplitude of a longitudinal wave

Underneath is the red line shown at its maximum displacement to the right. The distance it has moved is the amplitude of the oscillation. maximum displacement of a wave: This is less well understood, but is easy if you look at the word. Frequency means how frequent.

In other words, how often something happens. In physics, we normally expect frequency to be how many times something happens per second.

For a wave, frequency means: how many waves per second. Frequency has the unit of "per second", but we use a special unit for this: hertz (Hz). Like any unit, we can add prefixes in front of it to make alternatives:

e.g. 1 kilohertz = 1 kHz = 1,000 Hz
1 megahertz = 1 MHz = 1,000,000 Hz
1 gigahertz = 1 GHz = 1,000,000,000 Hz

You will no doubt be using a computer that has a speed of many mega-hertz, or even giga-hertz! The frequency of a set of waves is set at the source itself. For instance, if Billy pokes a pond with a stick twice each second, the frequency will be 2 Hz.

As the waves travel over the pond's surface, this frequency will not change. What may change is the distance between waves - the wavelength - and their speed. The relationship between the speed, frequency and wavelength is best found from a simple example.

Isobel sets up a ripple tank to produce 2 waves each second (i.e. frequency = 2 Hz). She times the waves 2 s to travel the 100 cm distance to the other side of the tank. She measures the distance between the waves as 25 cm: this is the wavelength.

A frequency of 2 Hz means one wave is produced every 0.5 s (this is known as the time period of the waves and is 1÷frequency).

In 0.5 s, waves move 25 cm, so we can find the speed using:

speed = distance / time = wavelength / time period = 25 cm / 0.5 s = 50 cm/s We can check the speed found using the length of the tank and the time taken:

speed = distance / time = 100 / 2 = 50 cm/s

So the relationship between speed, frequency and wavelength is:

wave speed = frequency x wavelength. v = f l.

Incidentally, the funny upside-down y is a greek letter called "lamda". You may need to know this formula! Let's put this new formula to good use by looking at a few more examples:

wave speed = frequency x wavelength. v = f l.

1. Bill counts 5 waves on a pond in 10 s. The distance between them is 80 cm. What is their speed?

2. Lizi reads the back label of her microwave oven. It says frequency = 2,450 MHz. The speed of microwaves is 3.00×108 m/s. What wavelength are they?

3. Paul plays a note of wavelength 25 cm on his syntheiser. He knows the speed of sound is 340 m/s in air. What is its frequency? Let's see how you got on:

1. 5 waves in 10 s. Distance between is 80 cm. Speed?
frequency = 5/10 = 0·5 Hz.
speed = frequency × wavelength = 0·5 × 80 = 40 cm/s

2. frequency = 2,450 MHz. speed = 3.00×108 m/s.
speed = frequency × wavelength
3.00×108 = 2,450×106 × wavelength
wavelength = 3.00×108 ÷ 2,450×106 = 0·122 m = 12·2 cm

3. wavelength= 25 cm = 0·25 m. Speed = 340 m/s
speed = frequency × wavelength
340 = frequency × 0·25
frequency = 340 ÷ 0·25 = 1,360 Hz
-Tan Chai Ming -http://www.gcse.com/waves/waves_summary.htm