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Waves in the Real World

In the top left, transverse sea waves are shown propagating towards the beach as a gust of wind blows. The surface of the water has a sine curve shape with peaks above the undisturbed water level, and troughs below. A seagull is pictured bobbing up and down vertically with the movement of the waves. In the top right, two spring toys are shown, both held hanging downwards by someone's hand. The movement of the hands is depicted with red arrows. For the first spring toy, the hand moves up and down, producing a longitudinal wave that propagates downwards through it, forming a repeating pattern of low and high density regions in its rings. To more clearly illustrate this, the positions of the individual rings are shown with blue horizontal lines, which share the same regions of high and low density. For the second spring toy, the hand moves side to side. This produces a transverse wave that propagates downwards through the spring as it takes a sine curve shape, with peaks and troughs. For comparison, a sine wave with the same wavelength and amplitude is drawn next to the spring in blue. In the bottom left, a guitar string has been plucked producing a transverse standing wave. The oscillation of the string is perpendicular to its length and is depicted with a red arrow. The string is shown at maximum displacement above its undisturbed position as a solid blue line, and below as a dashed blue line. The nodes of the standing wave, where there is no oscillation, exist at the two fixed endpoints. These are on the neck of the guitar where the player holds down the string, and on the bridge where the string is attached to the body of the guitar. A single anti-node, where there is maximum oscillation, exists at the midway point between these two nodes. Centre-bottom, a longitudinal sound wave is shown propagating away from a guitar. The positions of the individual air particles are depicted with blue vertical lines producing a repeating pattern of low and high density regions. The oscillation of a single air particle, parallel to the direction of propagation, is shown with a red arrow. In the bottom right, a light wave is shown propagating away from the Sun. The electric field is shown in blue and has a sine curve shape with peaks and troughs. Its oscillation, perpendicular to the direction of propagation, is depicted by a red arrow.

Figure 1: Different examples of waves present in day-to-day life.

Now that you have learned all about waves you will be able to identify them and their characteristics in the real world.

Sea waves lapping the shore are progressive, transverse waves and their medium is the water. They are most commonly caused when the water is disturbed by wind blowing across its surface.

Imagine holding a spring toy hanging down towards the ground. Bobbing your hand up and down will produce a progressive, longitudinal wave that propagates downwards through the rings of the spring. If you were instead to shake your hand side to side, this would produce a progressive, transverse wave.

When we pluck a guitar string it oscillates. This oscillation is a standing, transverse wave with a frequency that depends on the thickness, tension, and length of the string. The wavelength is twice the string length so we can only see half of one complete wavelength at a time. The thicker the string, the slower it oscillates, producing a lower frequency wave. As the guitar string moves it causes the air particles around it to oscillate too. This creates a progressive, longitudinal wave that travels through the air with the same frequency as the standing wave. When this wave reaches our ears we perceive it as sound. The lower the frequency the lower the pitch.

Light waves are a bit different from the others. They are progressive, transverse waves that propagate by oscillating electric and magnetic fields and can travel through empty space. This explains why we can see the Sun's light but we can't hear the raging nuclear reactions that produce it. Unlike light, the sound waves require a medium to travel through.