Waves are everywhere. We may think of them in terms of water waves or “The Wave” at stadiums, but we run into waves everyday in terms of sound waves, radio waves, light waves, microwaves, and for math students, sine and cosine waves, just to name a few.
Waves are everywhere in nature. Physicists study the nature, properties, and behaviors of waves. Generating a better understanding of waves helps them understand more about the physical aspects of our universe.
To help us visually think about waves, we can look at water waves, which most of us have observed at some point. A water wave carries energy and is made up of a crest and a trough. Waves move across the water carrying energy which may have begun through the action of wind, or an object falling into the water, or even the force of gravity, as with tidal movement.
We may also have encountered waves or wave-like functions in math class via the sine and cosine functions. There is also a repeating motion with crests and troughs in sines and cosines. We can change certain variables in the mathematical formulae describing these functions and thus change the length and/or height of the wave.
A wave of the sort we will talk about can be described as a disturbance that travels through a medium from one location to another. The medium is a series of interconnecting or interacting particles. The wave, caused by a disturbance, only temporarily displaces the particles from their rest position. The wave is an energy transporter, carrying energy from one location to another. A pulse is a single disturbance moving through the medium, but a repeated and periodic disturbance moving through a medium is a wave.
Waves come in many shapes and sizes. All waves share some basic characteristics, properties and behaviors. Some waves can be distinguished from others based on observable and some non-observable elements. One way is to categorize them on the basis of the direction of the movement of the particles of the medium relative to the direction the wave travels.
A transverse wave is a wave in which the particles of the medium move in a direction that is perpendicular to the direction the wave moves. An example can be shown with a slinky toy. If you stretched it out from left to right, then moved the first coil on the left up and down, the energy will be transported from left to right along the slinky. However, as the energy moves left to right, each individual coil will move up and down, meaning that the particles of the medium move perpendicular to the direction of the wave.
A longitudinal wave is one in which the particles move in a direction parallel to the direction in which the wave moves. Again, with a stretched out slinky, if you move the left-most coils in a left to right manner, the energy will move through the slinky from left to right and the individual coils will also move left to right. A sound wave is a classic example of a longitudinal wave.
Waves moving through a solid medium can be either transverse or longitudinal waves. Waves traveling through a fluid such as a liquid or a gas are always longitudinal waves. Transverse waves require a relatively rigid medium to transmit their energy. Earthquakes can generate both transverse and longitudinal waves. Scientists noted, however, that the only earthquake waves capable of traveling through the center core of the earth were longitudinal waves, leading them to conclude that the earth’s core is a liquid, and most probably molten iron.
A surface wave is a wave in which the particles of the medium undergo a circular motion. They are neither longitudinal nor transverse. This occurs only at the surface of the medium. The deeper one goes away from the surface, the more the motion of the particles tend to decrease.
Any wave moving through a medium has a source. Along the medium, there was an initial displacement in one (or more) of the particles. For instance vibration of vocal chords or a guitar string sets air particles in motion. As sound waves are longitudinal waves, the particles of air always move in the same direction away from the source of the vibration. Using a slinky again, a transverse wave is created when the first coil is displaced in a direction perpendicular to the stretched slinky, while a longitudinal wave is created when it is displaced in a direction parallel to the stretched slinky.
Another way of categorizing waves is on the basis of whether or not they can transmit energy through a vacuum, or through empty space. There are two types of waves based on this categorization.
The first is an electromagnetic wave. It is capable of transmitting energy through a vacuum or empty space. They are produced through the vibration of electrons within atoms on the surface of the Sun. These waves carry energy through the vacuum of space and reach the Earth. Life on Earth would probably not exist without electromagnetic waves. All light waves are examples of electromagnetic waves.
The second is a mechanical wave. They require a medium in order to transmit energy and thus cannot transmit through a vacuum. Sound waves are examples of mechanical waves. So are the examples we have already used, like slinky waves, water waves, and stadium waves.
Other ways of categorizing waves are numerous. For example, waves can be low energy or high energy transporters. This refers to the amount of force introduced as a pulse or series of pulses. High energy waves result from higher force being introduced, and is seen in a high wave amplitude. Low energy waves have lower forced used and show lower amplitude. Frequency relates to how close together the repeating waves are to one another and further relate to the speed of the pulse (or pulses) as it travels through the medium. Next time you are at a stadium and fans begin to do “The Wave” you can comment on whether it is a surface, transverse or longitudinal wave and speak to the frequency and amplitude.