PHYS 2211 Module 14.1

Traveling Waves

Learning Objectives

By the end of this section, you will be able to:

• Describe the basic characteristics of wave motion
• Define the terms wavelength, amplitude, period, frequency, and wave speed
• Explain the difference between longitudinal and transverse waves, and give examples of each type
• List the different types of waves

Types of Waves

A wave is a disturbance that propagates, or moves from the place it was created. There are three basic types of waves: mechanical waves, electromagnetic waves, and matter waves.

Basic mechanical waves are governed by Newton’s laws and require a medium. A medium is the substance a mechanical waves propagates through, and the medium produces an elastic restoring force when it is deformed. Mechanical waves transfer energy and momentum, without transferring mass. Some examples of mechanical waves are water waves, sound waves, and seismic waves.

A wave in which the particles in the medium move perpendicular to the direction that the wave travels along the medium is called a transverse wave. As a wave travels through a medium, the particles in that medium undergo displacements of different kinds depending on the type of wave.

A wave in which the particles in the medium move parallel to the direction that the wave travels along the medium is called a longitudinal wave.

A sound wave travels through a medium as a longitudinal wave and not a transverse wave.

A light wave does not require a medium to travel through and so there are no particles being displaced in a light wave.

A wave in which the particles in the medium move back and forth parallel to the direction that the wave travels along the medium is called a longitudinal wave. As a wave travels through a medium, the particles in that medium undergo displacements of different kinds depending on the type of wave.

A wave in which the particles in the medium move perpendicular to the direction that the wave travels along the medium is called a transverse wave.

A light wave does not require a medium to travel through and so there are no particles being displaced in a light wave.

A wave in a string is a transverse wave because the particles in the string move perpendicular, or transverse, to the length of the string.

As the wave in the string propagates to the right, one particle on the string moves up and down in simple harmonic motion. The periodic wave is produced by providing a periodic displacement to the end of the string, which is done with the block moving up and down in simple harmonic motion. As a result, every particle in the string moves up and down in simple harmonic motion.

The particles in the string move in the same way that the block moves since the motion of the block causes the displacement of the particles in the string. The particles in the string could not move right and left in simple harmonic motion since the block does not move that way. The particles in the string move in simple harmonic motion so they cannot move with a constant acceleration. The force acting on the particles in the string, which is a tension force, is not constant during this motion, so the acceleration of the particles in not constant.

The wavelength of this wave is the distance between one crest and an adjacent crest. The wavelength is also the distance from one trough to the next adjacent trough. 

The distance between a crest and an adjacent trough is equal to half the wavelength. The length of the string and the wavelength are not necessarily equal. The wavelength will depend on the speed of the wave and the frequency of the oscillation of the particles in the string.

The speed of this wave is . The speed is calculated by dividing the distance traveled by the interval of time. For this wave, the distance traveled is equal to the wavelength, , and the interval of time is equal to the period, T. The frequency, f, of the wave can be written as 1/T so the speed of the wave is when written in terms of the frequency.

This is the simulation I use in my videos: https://phet.colorado.edu/sims/html/wave-on-a-string/latest/wave-on-a-string_en.html

Go ahead and play around with it to learn more about waves traveling on a string.