Wave Characteristics

A wave is a disturbance of a medium which transports energy through the medium without permanently transporting matter. In a wave, particles of the medium are temporily displaced and then return to their original position.


There are a variety of ways to categorize waves. One way to categorize waves is to say that there are either transverse or compressional. In a transverse wave, particles of the medium are displaced in a direction perpendicular (a right angle) to the direction of energy transport. Look at the animation below and notice the water is not flowing. The water is actually vibrating at a right angle to the direction in which the energy is traveling.

Example of a transverse waves are electromagnetic waves such as; microwaves, radiowaves, and light. These types of waves are different from compressional waves because they do not require a substance(medium) to travel through. These are waves that can travel through the vacuum of space.

In a compressional wave, particles of the medium are displaced in a direction parallel to energy transport. Look at the animation below and notice that the energy is traveling parallel to the direction in which the particles vibrate.


Compressional waves, unlike electromagnetic waves, require the presence of a material medium in order to transport their energy from one location to another. Sound waves are examples of compressional waves.

Parts of a wave:

Crest (point A on the diagram): the highest point
Trough (point D on the diagram): the lowest point
Wavelength (points A to F or D to I on the diagram): the distance between one point on a wave and the nearest point just like it (crest to crest or trough to trough)
Frequency: number of wavelengths that pass a given point per second
Rest Position (the dotted line on the diagram): indicates no energy is present
Amplitude: indicates how much energy is found in the wave, the higher the vibrations, the more energy present.

Reflection, refraction and diffraction are all boundary behaviors of waves associated with the bending of the path of the wave. Reflection occurs when there is a bouncing off of a barrier. Reflection of waves off straight barriers follows the law of reflection. Refraction is the change in direction of waves which occurs when waves travel from one medium to another; refraction is always accompanied by a wavelength and speed change. Diffraction is the bending of waves around obstacles and openings; the amount of diffraction increases with increasing wavelength.

What happens when two waves meet while they travel through the same medium? What effect will the meeting of the waves have upon the appearance of the medium? Will the two waves bounce off each other upon meeting (much like two billiard balls would) or will the two waves pass through each other? These questions involving the meeting of two or more waves along the same medium pertain to the topic of wave interference. Wave interference is the phenomenon which occurs when two waves meet while traveling along the same medium. The diagrams below depict the before- and during interference snapshots of the medium for two such crests.


This type of interference is sometimes called constructive interference. Constructive interference is a type of interference which occurs at any location along the medium where the two interfering waves have a displacement in the same direction. In this case, the energy of both waves add together. Constructive interference is observed when a crest meets a crest; or a trough meets a trough. Destructive interference is a type of interference which occurs at any location along the medium where the crest or trough of two interfering waves meet. In this scenario there is a net loss of energy. Take a look at the diagram below:

The result is that the two pulses completely destroy each other when they overlap. At the instant of complete overlap, there is no resulting disturbance in the medium. Interestingly, the meeting of two waves along a medium does not alter the individual waves or even deviate them from their path. This only becomes an astounding behavior when it is compared to what happens when two billiard balls meet or two football players meet. Billiard balls might crash and bounce off each other and football players might crash and come to a stop. Yet waves meet, produce a net resulting shape of the medium, and then continue on doing what they were doing before the interference.

A standing wave is a pattern which results from the interference of two or more waves travelling in the same medium. All standing waves are characterized by positions along the medium which are standing still. Such positions are referred to as nodes. Nodes are the result of the meeting of a crest with a trough - energy is lost. Standing waves are also characterized by antinodes. These are positions along the medium where the particles oscillate with maximum amplitude. Antinodes are the result of a crest meeting a crest and a trough meeting a trough - energy is gained. Standing wave patterns are always characterized by an alternating pattern of nodes and antinodes.

Why do tuning forks produce different types of sounds? When you strike the fork, you cause it to vibrate at its natural frequency. There is another way to make something vibrate at its natural frequency. Suppose you have a tuning fork that haas a natural frequency of 440 Hz. Imagine that a sound wave of the same frequency strikes the fork. Because the sound wave has the same frequency as the tuning fork, the tuning fork will begin to vibrate; even without you touching it. The ability of an object to vibrate by absorbing energy at its natural frequency is called resonance. Why do some buildings crumble during an earthquake? If the ground is vibrating at the natural frequency of the building, the building will begin to vibrate. You can imagine the end result!

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