Student Exploration: Longitudinal Waves
Vocabulary: antinode, compression, displacement, frequency, interference, longitudinal wave,
medium, node, rarefaction, standing wave
Prior Knowledge Question (Do this BEFORE using
the Gizmo.)
In many science fiction movies, an evil alien
spaceship explodes with an enormous KABOOM!!
Suppose you were floating in space at a safe distance
from a large explosion such as the supernova at left.
Do you think you would you hear anything? Explain.
I don’t think so, the sound doesn’t have anything to
vibrate to make the noise in space.
Gizmo Warm-up
No sounds can be heard in outer space because sound waves
require a medium, such as air, to travel through. Sound waves
are examples of longitudinal waves, or waves in which
particles move back and forth in the same direction as the wave.
You can use the Longitudinal Waves Gizmo to explore the
behavior of sound waves. In the Gizmo, an air-filled tube
contains 24 evenly-spaced, airtight dividers. To begin, select the
Pulsed waves setting and the Open tube. Set the Strength to
1.00. Deselect the graph options at lower right.
1. Click Play ( ) to set off the firecracker by the left end of the tube. What do you see?
The wave moves left and right and then back. Also, it also dips below 0 on the second round
and every other one after.
2. Do any individual air molecules travel the length of the tube? I think they do.
How do you know? The airtight dividers didn’t block the air molecules from travelling
through.
2019
Activity A:
Observing
longitudinal
waves
Get the Gizmo ready:
 Click Reset ( ).
 Select Continuous waves. Check that the
Strength is 1.00 and Freq. is 30 Hz.
Introduction: When you strike a tuning fork on a hard surface, the tines of the fork start to
vibrate back and forth at a certain frequency, or number of cycles per second. This motion
causes nearby molecules to move back and forth, creating sound waves. The greater the
frequency of the sound wave, the higher pitched the sound will be.
Question: What happens to air as a sound wave passes through it?
1. Observe: Click Play, and then click Pause ( ) after about 70 simulated milliseconds (does
not have to be exact). Sketch the current positions of the dividers below.
2. Identify: Longitudinal waves have two important features. Compressions are regions where
particles are squished together. Rarefactions are regions where particles are spread apart.
In your diagram above, draw a red rectangle around each compression and a blue oval
around each rarefaction. (Note: The dividers were originally spaced one meter apart.)
3. Observe: Turn on the Displacement graph. The displacement of a divider is equal to the
change from its original position. The original positions of the red and green dividers are
shown by the red and green dots below the tube.
In which direction has the red divider moved? The red divider has moved to the right. The
green divider? The green divider has moved to the left.
4. Interpret: Compare the displacement graph to the dividers in the tube.
A. How does the graph represent movement to the right? It has the wave above the x
axis.
B. How does the graph represent movement to the left? It has the wave below the x
axis.
(Activity A continued on next page)
Student Exploration: Longitudinal Waves
Vocabulary: antinode, compression, displacement, frequency, interference, longitudinal wave,
medium, node, rarefaction, standing wave
Prior Knowledge Question (Do this BEFORE using
the Gizmo.)
In many science fiction movies, an evil alien
spaceship explodes with an enormous KABOOM!!
Suppose you were floating in space at a safe distance
from a large explosion such as the supernova at left.
Do you think you would you hear anything? Explain.
I don’t think so, the sound doesn’t have anything to
vibrate to make the noise in space.
Gizmo Warm-up
No sounds can be heard in outer space because sound waves
require a medium, such as air, to travel through. Sound waves
are examples of longitudinal waves, or waves in which
particles move back and forth in the same direction as the wave.
You can use the Longitudinal Waves Gizmo to explore the
behavior of sound waves. In the Gizmo, an air-filled tube
contains 24 evenly-spaced, airtight dividers. To begin, select the
Pulsed waves setting and the Open tube. Set the Strength to
1.00. Deselect the graph options at lower right.
1. Click Play ( ) to set off the firecracker by the left end of the tube. What do you see?
The wave moves left and right and then back. Also, it also dips below 0 on the second round
and every other one after.
2. Do any individual air molecules travel the length of the tube? I think they do.
How do you know? The airtight dividers didn’t block the air molecules from travelling
through.
2019
Activity A:
Observing
longitudinal
waves
Get the Gizmo ready:
 Click Reset ( ).
 Select Continuous waves. Check that the
Strength is 1.00 and Freq. is 30 Hz.
Introduction: When you strike a tuning fork on a hard surface, the tines of the fork start to
vibrate back and forth at a certain frequency, or number of cycles per second. This motion
causes nearby molecules to move back and forth, creating sound waves. The greater the
frequency of the sound wave, the higher pitched the sound will be.
Question: What happens to air as a sound wave passes through it?
1. Observe: Click Play, and then click Pause ( ) after about 70 simulated milliseconds (does
not have to be exact). Sketch the current positions of the dividers below.
2. Identify: Longitudinal waves have two important features. Compressions are regions where
particles are squished together. Rarefactions are regions where particles are spread apart.
In your diagram above, draw a red rectangle around each compression and a blue oval
around each rarefaction. (Note: The dividers were originally spaced one meter apart.)
3. Observe: Turn on the Displacement graph. The displacement of a divider is equal to the
change from its original position. The original positions of the red and green dividers are
shown by the red and green dots below the tube.
In which direction has the red divider moved? The red divider has moved to the right. The
green divider? The green divider has moved to the left.
4. Interpret: Compare the displacement graph to the dividers in the tube.
A. How does the graph represent movement to the right? It has the wave above the x
axis.
B. How does the graph represent movement to the left? It has the wave below the x
axis.
(Activity A continued on next page)