Longitudinal Wave: Definition, Parts & Examples

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• 0:02 What Is a Longitudinal Wave?
• 1:23 Sound Is a Longitudinal Wave
• 1:55 The Parts of a…
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Lesson Transcript
Instructor: Mary Ellen Ellis
There are a few different kinds of waves, including the longitudinal wave. This type of wave occurs when the particles of a medium move in the same direction as the wave itself.

What Is a Longitudinal Wave?

Did you ever play with a Slinky as a kid? If you did, you probably made it walk down the stairs, but did you also pinch several of the loops together and let them go? If you did, you would have seen that a compressed area of the slinky moves like magic from one end to the other. Looking closely, you would have seen the compressed loops move forward, trailed by an area of the slinky loops that were stretched out. You created a longitudinal wave.

To better understand what this means, let's go back to what a wave is. A wave is a disturbance that moves through a medium. When you think of a wave, you probably immediately think of the beach and water waves. Using that as an example, the medium is the water and the disturbance is the up-and-down movement of the water.

A longitudinal wave is a wave in which the disturbance moves in the same direction as the propagation of the wave. Going back to the Slinky example, the medium is the slinky, and the disturbance is the back-and-forth movement of the slinky. Notice how this description differs from the description of the water wave: up-and-down vs. back-and-forth movement.

The disturbance in the slinky occurs when you pinch the loops of the toy together. When you let it go, that disturbance moves parallel, or in the same direction as the wave that you observe moving along the length of the slinky. The water wave is the opposite in that the disturbance moves up and down, while the wave moves toward the beach.

Sound Is a Longitudinal Wave

Another example of a longitudinal wave that you experience every day, but can't see, is a sound wave. Let's use the example of someone talking to you. When your friend says hello, her vocal cords vibrate. This provides the disturbance needed to create a longitudinal wave. The medium is the air, and the vibrations cause a disturbance in the particles that make up air. The longitudinal wave travels through the air to your ear. The small organs inside your ear pick up the vibrations and transmit them to your brain where you interpret the sounds.

The Parts of a Longitudinal Wave

A longitudinal wave can occur in any medium. Something creates a disturbance in the particles of the medium, and a wave moves outward from that source. There are different parts to this type of wave that can be applied to any example. A compression is where the particles of the medium are closest together, like when you pinch the slinky loops together. A rarefaction is where the particles are stretched apart. The point halfway between the middle of a compression and the middle of a rarefaction is when the particles of the medium are at rest; in other words, neither compressed nor stretched out.

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