In our article on the properties of waves, we discussed the huge importance of waves for our lives and our technologies.
Our bodies are developed to use sound waves to detect vibrations around us and to hear with. Our eyes use light waves to turn a reflection of an object into an image that we understand. Meanwhile, we have developed radio waves – which are a type of light – to transmit information remotely, whilst we can now harness the energy from water waves for our society’s use.
Alongside these quite useful waves, there are the seismic waves that are unleashed by earthquakes and volcanoes. Electromagnetic waves that are produced by the interaction of a magnetic field and an electric field. And the waves are the basic fact of fun things like trampolines and a Mexican wave.
Waves are all around us, in places that we may never have expected. It is therefore so important that we take the time to understand what the hell these things actually are: how they work, their main features and properties, and the main characteristics that their different types exhibit.
The latter is what we are going to be doing here. We’ll focus on the two main types of wave – longitudinal and transverse – and show you the different places in which you can find each. We’ll point you in the direction of surface waves – a combination of the two – whilst we’re here.
We hope you find it interesting!
What is a Wave?
Do you remember the definition of a wave? Scientists tend to define it as a disturbance or variation that transmits energy in a regular way. Every part of this definition is important, so let’s take a moment to unpack it.
In mechanical waves – i.e. waves that require a medium through which to pass – the particle matter that facilitates the wave’s energy transfer is disturbed. As the wave’s energy passes through the matter, the particles move and then return to their original position – so that there is a net movement of zero.
It is only energy that is being transmitted in a mechanical wave, then, not mass. But the energy passing through the medium produces oscillations – and these are necessarily regular.
If they were not – if they were just completely random – you would not have a wave. In this case, there would have to be some external source of energy affecting medium that is not the simple travel of energy from point to point.
So, to recap, waves
- are a disturbance in a medium;
- have to be regular in their disturbance; and
- transfer energy from point to point.
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Longitudinal Waves and Transverse Waves
So, now that we have cleared that up, let’s move on to the real content of this article – the nature of and difference between the longitudinal wave and the transverse wave.
Do you have any idea of this difference? If you’ve read our article, What are Waves? you might well be on the money. Yet, here we’re going to take it in a little more detail.
The difference between longitudinal and transverse waves is all about the wave motion – namely how the waves oscillate. If a wave produces material movement that is perpendicular to the direction of the energy transfer, we call this sort of wave transversal. If the movement is rather parallel to the direction of transferred energy, we call the wave longitudinal.
For clarity, let’s take these one at a time.
What are Transverse Waves?
If there were such a thing as a ‘classic’ wave, it would be the transverse wave. These are the familiar sorts of waves that we study in diagrams. We do this because the transverse waves are the easiest waves to visualize – as they demonstrate a polarization that we can see extending into space.
Think of a skipping rope. As you flick it, a visible wave travels from your hand down the length of the rope. This is a transverse wave.
The scientific definition for a transverse wave is that the displacement of the medium is at right angles to the direction of energy transmission. Thinking of the skipping rope again, that means that the visible wave travels ‘up and down’, the energy travels down the length of the rope.
- In transverse waves, the particles of the medium vibrate perpendicular to the direction in which the wave is traveling.
- The most common example of a transverse wave is a water wave, where water particles move up and down as the wave passes through.
- Other examples include electromagnetic waves like light and radio waves, where the electric and magnetic fields oscillate perpendicular to the direction of propagation.
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Peaks and Troughs
We call the highest point of a wave – that moment of maximum displacement of the medium – in a transverse wave the ‘peak’ when it is ‘up’ and a ‘trough’ when it is ‘down’.
Consequently, with a transverse wave, we can easily measure the wave’s wavelength as well as its amplitude. ‘Easily’ at least theoretically. Because, again, you can see the distance between the peaks (through which we measure the length of the wave’s oscillation or its wavelength) as well as the distance between the peaks and the wave’s rest position (the amplitude of the wave).
Both of these – wavelength and amplitude – can tell us the amount of energy being transferred in the wave.
Examples of Transverse Waves
Transverse waves are a type of mechanical wave in which the particles of the medium vibrate perpendicular to the direction of wave propagation. This is in contrast to longitudinal waves, in which the particles vibrate parallel to the direction of wave propagation.
Examples of transverse waves include:
- Water waves: When a stone is dropped into a pond, it creates a series of concentric circles of waves that move outward from the point of impact. The water particles vibrate up and down as the waves pass through them.
- Sound waves: Sound waves are created when an object vibrates, causing the air particles around it to vibrate. The air particles vibrate back and forth in the same direction as the wave is traveling.
- Electromagnetic waves: Electromagnetic waves, such as light and radio waves, are also transverse waves. The electric and magnetic fields of these waves vibrate perpendicular to the direction of wave propagation.
Transverse waves can be described by several properties, including:
- Wavelength: The wavelength of a wave is the distance between two adjacent peaks or troughs.
- Frequency: The frequency of a wave is the number of waves that pass a given point in one second.
- Amplitude: The amplitude of a wave is the maximum displacement of the particles from their equilibrium position.
- Speed: The speed of a wave is the distance that the wave travels in one second.
The speed of a transverse wave is determined by the properties of the medium through which it is traveling. In general, the denser the medium, the slower the wave will travel. The speed of a transverse wave is also affected by the frequency of the wave.
Higher frequency waves travel faster than lower frequency waves.
A guitar string works in the same way as the skipping rope – except the frequency of the wave is much higher.
Electromagnetic waves such as light and radio waves are also transverse. In their disturbance of the magnetic field, they polarize alternately – meaning when the electric wave is peaking, the magnetic aspect is in a trough.
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What are Longitudinal Waves?
Longitudinal waves are a type of mechanical wave in which the particles of the medium vibrate parallel to the direction of the wave's propagation. In simpler terms, the particles move back and forth along the same line as the wave is traveling.
Longitudinal waves can occur in solids, liquids, and gases. In solids, the particles are held together by strong intermolecular forces, so they can only vibrate back and forth over short distances. In liquids, the particles are more loosely bound, so they can vibrate over longer distances. In gases, the particles are very loosely bound, so they can vibrate over the longest distances.
The speed of a longitudinal wave depends on the medium through which it is traveling. In general, the denser the medium, the slower the wave. For example, sound waves travel faster through solids than through liquids and gases.
Longitudinal waves are used in a variety of applications, including:
- Sound waves: Sound waves are longitudinal waves that travel through the air. When an object vibrates, it creates sound waves that can be heard by our ears.
- Ultrasonic waves: Ultrasonic waves are high-frequency sound waves that are used in a variety of applications, such as medical imaging and cleaning.
- Seismic waves: Seismic waves are longitudinal waves that travel through the Earth. They are used to study the Earth's interior and to detect earthquakes.
- In longitudinal waves, the particles of the medium vibrate parallel to the direction in which the wave is traveling.
- A simple example of a longitudinal wave is a sound wave, where air particles move back and forth in the same direction as the wave propagates.
- Another example is a compression wave in a spring, where the coils of the spring move closer together and then apart in the same direction as the wave travels.
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Compressions and Rarefactions
Scientists call these movements compressions and rarefactions, and they are the longitudinal equivalent to the transverse peaks and troughs.
Compressions are the areas in the medium in which the particles – or the rings of the slinky – are closer together. Here the pressure is very high, which means that the medium can push itself apart again. The rarefaction, meanwhile, are areas of low pressure; they are the areas where the particles of the medium are further apart.
If you were to measure the amplitude or frequency and wavelength of a longitudinal wave, you would take the measurement from the points of highest compression.
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Examples of Longitudinal Waves
- Sound waves: Sound waves are longitudinal waves that travel through the air, water, or other media. When sound waves reach our ears, they cause the eardrums to vibrate, which sends signals to the brain that we interpret as sound.
- Pressure waves: Pressure waves are longitudinal waves that travel through fluids. They can be caused by a variety of things, such as explosions, earthquakes, or the movement of objects through the fluid.
- Seismic waves: Seismic waves are longitudinal waves that travel through the Earth. They are caused by earthquakes and can be used to study the Earth's interior.
Longitudinal waves can also be created in solids, but they are not as common as in fluids. One example of a longitudinal wave in a solid is the vibration of a guitar string.
The speed of a longitudinal wave depends on the medium through which it is traveling.
In general, longitudinal waves travel faster in solids than in liquids and gases. The speed of sound in air at room temperature is approximately 343 meters per second (1,235 kilometers per hour).
Longitudinal waves are used in a variety of applications, such as:
- Communication: Sound waves are used for communication in a variety of ways, including speech, music, and telephone conversations.
- Medical imaging: Ultrasound waves are used to create images of the inside of the body.
- Non-destructive testing: Ultrasonic waves are used to test for defects in materials.
- Seismology: Seismic waves are used to study the Earth's interior.
Difference Between Longitudinal And Transverse Waves
Transverse and longitudinal waves are two main types of mechanical waves that differ in their direction of particle displacement relative to the direction of wave propagation.
Transverse waves:
- In transverse waves, the particles of the medium vibrate perpendicular to the direction in which the wave is traveling.
- The most common example of a transverse wave is a water wave, where water particles move up and down as the wave passes through.
- Other examples include electromagnetic waves like light and radio waves, where the electric and magnetic fields oscillate perpendicular to the direction of propagation.
Longitudinal waves:
- In longitudinal waves, the particles of the medium vibrate parallel to the direction in which the wave is traveling.
- A simple example of a longitudinal wave is a sound wave, where air particles move back and forth in the same direction as the wave propagates.
- Another example is a compression wave in a spring, where the coils of the spring move closer together and then apart in the same direction as the wave travels.
In summary, transverse waves involve particle motion perpendicular to the wave's direction, while longitudinal waves involve particle motion parallel to the wave's direction. Both types of waves can propagate through various media, including solids, liquids, and gases.
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