Student Exploration: Longitudinal Waves
Prior Knowledge Questions (Do these
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, I think 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 GizmoTM 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 oscillates left to right and then back, and then dips below 0 on the second
round and every other one after.
2. Do any individual air molecules travel the length of the tube? How do you know?
I think they do, the airtight dividers don’t block the air molecules from travelling
through.
Page 1 of 8
, Student Exploration: Longitudinal Waves
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.
I don’t know how to draw on that picture, but it is tight at the beginning and then spreads
out and then becomes tight again. (compression>rarefaction>compression)
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 green divider?
The red divider has moved to the right and the green divider has moved to the left.
Page 2 of 8
Prior Knowledge Questions (Do these
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, I think 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 GizmoTM 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 oscillates left to right and then back, and then dips below 0 on the second
round and every other one after.
2. Do any individual air molecules travel the length of the tube? How do you know?
I think they do, the airtight dividers don’t block the air molecules from travelling
through.
Page 1 of 8
, Student Exploration: Longitudinal Waves
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.
I don’t know how to draw on that picture, but it is tight at the beginning and then spreads
out and then becomes tight again. (compression>rarefaction>compression)
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 green divider?
The red divider has moved to the right and the green divider has moved to the left.
Page 2 of 8
