The physics behind burbling water

This exercise is a part of Educator Guide: Water Burbling Physics and THC and the Teenage Brain / View Guide
Three images show water being poured from a teapot. The shape of the droplets is described by an effect known as Rayleigh-Plateau instability.
A stream of water poured from a teapot forms ridges as it falls before breaking up into individual droplets. These features affect how air bubbles form in the liquid (bottom left), explaining the variation in the sound of water poured from different heights.Ho-Young Kim et al, APS 2023

Directions for teachers:

The sound of running water is common to us all, and your class can easily investigate the physical scientific principles behind this phenomenon. Start off this lesson by calling students’ attention to the phenomenon. If time is available, take students out for a nature walk to an active creek. Or you could bring a fountain to class or play a calming water sounds video as students enter the classroom. You could simply turn on your classroom faucet or pour water out of a pitcher into a glass. Have students take a few moments to individually answer the first set of questions (“Familiar sounds”). 

Then have your students investigate the phenomenon by experimenting on their own to identify variables that impact the water’s sound and its volume. Set up your classroom so that each group can do their own water pouring experiment. Have students work through questions 1-5 in their group and then come together as a class to share results. Finally, either in class or for homework, have them read the Science News article “Here’s the science behind the burbling sound of water being poured” and answer the last set of questions  (“The science of burbling water”).

Review sound waves with your students using the Introduction of this Science News Learning activity.

List of materials:

  • Pitchers
  • Plastic tubs
  • Straws
  • Squeeze bottles
  • Water bottles
  • Thermometer
  • Hot and cold water
  • Camera on phone or other device
  • Pen or pencil to record observations

Directions for students:

Answer the following questions as directed by your teacher.

Familiar sounds

1. What do you think of when you hear water burbling? How does it make you feel?

Student answers will vary.

2. Many commercial products, such as fountains and sound machines, incorporate the sounds produced from pouring or running water. What do think is the purpose of such products?

Students may say that the products drown out other noises, create a calming environment, promote relaxation, reduce stress, etc.

3. How could you create your own device to produce these water sounds? What would you have to investigate before you began developing a device?

Students should begin to think about what conditions and variables create and impact the sounds of water. For instance, I could use a pump to create a fountain. If the water flowed over a group of rocks, it might make soft bubbling sounds. But the sound might depend on the speed of the flow. If the water flowed too fast, it might not sound relaxing or could make a mess.

Making noise with water

With your group, using the materials provided, try to make the loudest sound you can by pouring water from one receptacle into another. Try manipulating as many variables as you can. Keep track of how loud you perceive the sounds to be or use an app for measuring sound volume. Once you’ve found the loudest sound you can make, take a video of your demonstration. Then, still pouring water from one receptacle to another, try to make the quietest sound you can. Once you’ve found the quietest sound, take a video of your demonstration.

1. What variables did you manipulate as a part of your water experiments? List them.

Temperature of water, height water was poured from, rate that water was poured from one receptacle to another, the type of vessel water was poured from and into, and how the vessels affected the size of the stream of water that was being poured.

2. How did you manipulate the variables to make the loudest sound? How about the quietest sound?

Student answers will vary but may say that water poured from a higher height made a louder sound and water poured from a lower height made a quieter sound.

3. Watch the videos of your demonstrations. How did the streams of water differ in the two videos? Explain the differences you observe.

Student answers will vary, but generally, thinner streams of water will create a louder sound than bigger streams of water.

The science of burbling water

1. Read the Science News article “Here’s the science behind the burbling sound of water being poured.” What did the scientists find makes the loudest sounds? Do the scientists’ findings agree with yours?

Student answers will vary. In the article, scientists found that a column of falling water that develops ripples or breaks up into droplets produces the loudest sound. The higher the height that water was poured from and the thinner the column of water, the more likely it was for ripples to form or the stream to break into droplets before impact. Those conditions produced the loudest sounds.

2. Explain where the sound you hear when pouring water comes from.

The sound comes from the air bubbles produced when the stream of water hits the surface of the water in the container. The air bubbles vibrate and cause air molecules to vibrate and collide with other molecules.

3. If you could perform the experiment again, are there any variables you would change to make a louder or quieter sound? Explain.

Student answers will vary. Students may note that they could decrease the height they are pouring from or use a vessel with a larger spout to try to make a quieter sound. On the other hand, they could increase the height or use a vessel with a smaller spout to try to make a louder sound.