Waves Physics

Waves in Physics are a form of energy transmission. Classically, we see waves as the oscillation caused by energy transmission through a medium. As waves are defined simply as energy transmission in the form of oscillations, there are many different types of waves, such as electromagnetic waves, water waves, or gravitational waves.

What are progressive and stationary waves?

We can divide waves into stationary waves and progressive waves. Stationary waves do not propagate as they oscillate up and down in the same place. An example of this is the guitar strings when you play the guitar. Progressive waves move from one place to another. A classic example of a progressive wave is an ocean wave.

Figure 1. A progressive wave moves from one place to another. Source: StudySmarter.

Figure 2. A stationary wave does not move from one place to another. Stationary waves are oscillations that appear and disappear in fixed points of space, as shown above. Source: StudySmarter.

Representing simple waves

To represent simple waves, we use the two simple mathematical functions of sine and cosine, which have cyclical oscillation patterns. You find these in all the mathematics linked to waves.

Figure 3. The sine and cosine functions are used to represent simple waves due to their oscillating behaviour. Source: StudySmarter.

The sine and cosine functions describe certain properties and characteristics that help us to understand waves:

• Amplitude: the height of the wave over the plane of equilibrium. If it is positive, we are dealing with a crest; if negative, we are looking at a trough.
• Crest: the maximum amplitude of the wave from the plane of equilibrium.
• Trough: the maximum negative amplitude measured from the plane of equilibrium.
• Wavelength: the length of a wave from a crest to the next crest, which is denoted by the symbol ‘λ’ and measured in metres.
• Wave height: denoted by the symbol ‘H’ and measured in metres, the wave height ‘H’ is the vertical distance between the crest and trough.
• Period: the time it takes for a wave to repeat its oscillation pattern, which is denoted by the symbol ‘T’ and measured in seconds.
• Frequency: the number of times a wave repeats during a time interval equal to a second, which is denoted by the symbol ‘f’ and measured in hertz.
• Wave speed: the velocity at which a wave moves, which is denoted by the symbol ‘c’ and measured in m/s.

Figure 4. Two very important parameters of a wave are its height (H) and wavelength (λ), both of which depend on its dimensions. Source: StudySmarter.

Examples of waves in nature

• Wind waves: the waves you see on the beach or in the ocean are created by the wind blowing over the ocean’s surface.
• Sound waves: vibrations that are the product of mechanical waves moving through air. The source of vibrations is an object moving at high speed, such as a guitar string.
• Radio waves: electromagnetic waves that are the product of charges oscillating rapidly.
• Seismic waves (earthquakes): occurring in solids, these are mechanical waves that are the product of the moving of tectonic plates.
• Vibration waves: produced by the movement of a material, these are similar to seismic waves and also move in solids.
• Gravitational waves: the product of masses oscillating in space, these propagate in the fabric of space.

Waves that transport mass

When waves are progressive in nature, they move from one place to another, as in the case of sea waves. However, in addition to this, sea waves also carry water with them. Progressive waves can also occur in the atmosphere.

Transport of energy in waves

Progressive waves, therefore, can transfer not only mass but also energy. To be precise, they transport kinetic energy as they move across the medium, causing it to vibrate up and down. Examples of this are ocean, sound, and seismic waves. The energy transfer, which is parallel to the movement of the wave, is easily seen as waves move from one place to another.

Mechanical waves in solids

Waves can also appear in solid materials, in which case they act as seismic waves. These waves only transport energy within the material. If, for instance, you knock over a table, you can feel the vibrations inside the table with your hands. These vibrations are seismic waves propagating through its body.