Gravity Tube

Driving Questions:

• 1. What do you observe when you hold the gravity tube vertically and then reverse the orientation, holding the tube with the other end down? Examine both ends of the gravity tube and note the difference between them. What happens to the piece inside the tube when you hold the tube vertically? What is the function of this piece?

     1. If you hold the gravity tube vertically, the open end of the gravity tube will create a higher pitch and the closed end will create a lower pitch. However, they both will create a sound. The piece inside the tube creates the sound when it slides down.

  2. Repeat your observations with all of the gravity tubes you have. Do they all work the same way or are there variations between them? Do they all sound the same or do some have different pitches or loudness?

• • 1. They all work the same and they sound the same.

• 3. What happens to the sound if you shake the tube vertically? How does the tube sound if you shake it with the open end downward? How does this sound compare to the sound made when you shake it with the closed end downward? How can you use the terms "grave" and "shrill" to describe the sound produced by the tube?

• • 1. If you shake the tube vertically, the open end of the gravity will create more of a shrill sound because it has a higher frequency. The closed end will create more of a grave sound because it has a lower frequency. The pitch increases by shaking the gravity tube.

• 4. What happens if you hold the gravity tube vertically and then throw it, still oriented vertically, to a partner? Does the sound continue or stop while the tube is in the air? How can you explain this?

• • 1. The sound will stop while the tube is in the air. The piece has to fall down in order to create a sound. Since, it is in free fall the piece in the tube does not fall with respect to the gravity tube. Therefore it doesn’t create any sound.

• 5. What happens to the length of the column of air inside the gravity tube as the inner piece changes position?

• • 1. It will either increase or decrease the length of the column of air inside the gravity tube.

• 6. The noisemaker in the gravity tube sets up a standing wave in the column of air vibrating inside the tube. Is the tube an example of a closed pipe or an open pipe configuration? What kind of standing wave can exist inside this type of tube?

• • 1. The tube is an example of opened-opened and opened-closed pipe configurations. Standing waves depend on each side of the gravity tube. Waves usually travel within the column of the air inside the tube which makes it meet a boundary of the air at the atmospheric pressure. So it causes the end of the pipe to open and some waves will continuously travel into the tube when the other waves are reflected by the interface between the air with different pressures. If one side is opened and the other side is closed, its standing wave has a multiple of 1/4 wavelength which is a quarter. If they are both opened, its standing wave has a multiple of 1/2 wavelength which is half.

7. The equation v = f x λ relates the speed of a wave to its wavelength and frequency. How can you demonstrate this relationship with the sound produced by the gravity tube? How is the pitch of the sound related to its wavelength and frequency?

The open end of the gravity tube’s wavelength decreases so it has a higher frequency and a higher pitch and the closed end of the gravity tube’s wavelength increases so it has a lower pitch and a lower frequency.

8. How can you demonstrate constructive interference with the gravity tubes? What is the relationship between constructive interference and sound amplitude?

If you hold more than 1 gravity tube at once and hold it vertically, the amplitude of the sound will increase. However, the pitch or the frequency doesn’t change.