Compression Waves

Lesson Plan - Get It!

Audio:

That may seem like an odd question.

When you think of sound, you typically do not associate it with a geometrical shape.

Sound has to be able to travel. It is what causes you to hear music that is playing in another room, and allows you to hear what your friend is saying as the words travel from his or her mouth to your ears. The shape that sound takes is what allows it to travel.

To discover the shape of sound, you are going to watch a video. Sound is typically invisible, but scientists have found a way to show what it looks like.

As you watch The Rubens' Flame Tube: Seeing Sound Through Fire (Jeff Regester), draw pictures of the shapes you see as the volume and pitch change:

• What shapes did you draw?

While the images varied slightly depending on the volume and pitch, the sound always took the form of a wave. Scientists call these waves compression waves. Another name for a compression wave is longitudinal wave, because the molecules vibrate parallel (side-to-side) to the direction the wave is traveling.

Remember, sound is created by vibrating molecules. As these molecules vibrate back and forth, they move in a forward direction, allowing sound to travel. In some areas, the molecules are pressed together and in other areas, they are more spaced out. This is what causes the wave to take shape.

Try this experiment with a partner:

1. Get out a toy Slinky. 
2. With your partner, lay the Slinky on the floor. 
3. Have your partner hold one end of the slinky while you hold the other end. 
4. Each person should push his or her end of the slinky in a back-and-forth motion, pushing the Slinky away from his or her body and then pulling it backwards. 
5. This will cause a ripple effect in the Slinky, which provides a good illustration of what a compression wave looks like.

• Have you ever been attending a concert or watching television, and it appears the sound does not match up with what you are seeing?

For example, maybe a character's mouth starts moving before you actually hear what he or she is saying. This is because sound is not instantly heard everywhere.

Remember, sound waves have to travel to you. So, a person sitting next to the stage at a concert will hear the music before the people sitting in the back of an arena.

To learn more about how sound waves travel, watch Physics of Football - Sound Waves (Hail State):

• What is the speed of sound?

It's hard to believe that sound is traveling at 760 miles per hour! That's fast!

Move on to the Got It? section to assess what you have learned about sound and compression waves.