Pitch and Volume

Once students understand how waves transfer energy, they focus on a wave’s frequency and the factors that affect the pitch of sound produced by a stringed instrument. 

• Sound moves more quickly through liquids than it does through gasses because of how sound energy moves through matter.  
• Frequency is the number of waves that pass a set point in a given amount of time, and a wave with a higher frequency carries more energy than a wave with a lower frequency if both waves have the same amplitude.
• Frequency is closely related to pitch, which describes how high or low a sound seems.
• Sound travels about four times faster in the water than it does in the air. This is because the molecules in a liquid are closer together than in a gas.  
  
  

• What can you infer about the relationship between a wave’s frequency and the amount of energy it carries?
• How does sound move through the classroom from the teacher’s voice to your ears?
• How would you expect the movement of the sound to change if the teacher made the sounds underwater?
• How would you describe the pitch of the average human male’s speaking voice compared to that of an average human female’s speaking voice?
• Why do you think that blue whales, which are described in the reading as the largest animals on Earth, have such low vocalizations that they are inaudible to human ears?
• How are musical instruments designed with knowledge of the relationship between wave frequency and pitch?  
• Why do some instruments produce high- and low-pitch sounds?
• How could we make a stringed instrument have a higher pitch? What about a lower pitch?  
  
  

Misconception: Hitting an object with more force changes the pitch of the sound it makes.

Fact: Hitting an object harder changes the volume of the sound produced, but it doesn’t change the pitch. Pitch is determined by a wave’s frequency and is how high or low a sound seems, not how loud or soft.

Amplitude:  a measure of the wave’s displacement from its resting position

Frequency:  the number of waves that pass a set point in a given amount of time

Pitch:  how high or low a sound seems

Vibrate:  to move back and forth quickly

Wavelength:  the distance spanned by one cycle of the motion of a wave

The “Loneliest Whale”

Mary Ann Daher has received many emails from people interested in one specific whale in the North Pacific Ocean.

This whale may be a blue whale. No one knows for sure. No one even knows if they’ve seen it. But many people have heard it. This whale has become known as the “loneliest whale in the world.”

Mary Ann doesn’t call the whale lonely. Other scientists don’t either. They don’t even know if whales get lonely. But non-scientists have called the whale lonely. A singer from Michigan wrote a children’s song about this whale. An artist in upstate New York made a sculpture of this whale.

How Whales Communicate

Why do so many people call this whale lonely? It has to do with how this whale communicates compared to other blue whales.

Blue whales are the largest animals on Earth. They are also the loudest animals on the planet. They communicate with other whales that are sometimes thousands of miles away. They make low grunts, moans, and clicks.

Sound is a useful way to communicate in the ocean. Sound travels about four times faster in the water than it does in the air. This is because the molecules in a liquid are closer together than in a gas. As a result, the molecules collide with one another more quickly in a liquid than in a gas because they don’t have to move as far to come into contact with one another.

Sound Frequencies

If you were to stick your head under water in the middle of the ocean, you likely wouldn’t be able to hear the sounds of blue whales. This is because these sounds are at much lower frequencies than people can hear.

Frequency is the number of waves that pass a set point in a given amount of time. It is measured in hertz (Hz). Frequency is closely related to pitch, which describes how high or low a sound seems. A wave with a higher frequency has a higher pitch than a wave with a lower frequency.

Most blue whales vocalize in the range of 15 to 25 Hz. These sounds are so low they are almost completely undetectable by human ears.

Vocal Cords

Humans can hear sounds at frequencies from about 20 Hz to 20,000 Hz. Human speech is around 1,000 Hz to 5,000 Hz. The average human male speaking voice has a range between 85 and 155 Hz. The range for women is about 164 Hz to 255 Hz. For a child, it is about 250 Hz to 400 Hz. Baby cries are about 500 Hz.

The structure of our vocal cords explains why men generally have lower-pitched voices than women. Vocal cords are folded membranes that vibrate, producing sound. Adult men have longer and thicker folds than adult women. Both of these factors produce lower-pitched sounds. Children have much shorter vocal cords than adults have.

In addition to length and width, tension also affects a sound’s pitch. Tension refers to how tightly something is stretched. An object with more tension produces a higher frequency sound than an object with less tension.

In this lesson, students carry out an experiment to figure out the factors that affect the phenomena of sound. Students create devices that produce sounds with string and then evaluate how a sound’s pitch is related to its frequency and can be changed by altering certain factors in their prototypes.