Longitudinal Waves GIZMO ( ALL ANSWERS CORRECT ) NEW TOP PREDICTION Latest 2023/2024

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.

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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)

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2019

Activity A (continued from previous page)

5. Analyze: Compare the displacement graph to the tube. What do you notice about the

displacement near the center of a compression or a rarefaction? The displacement is near 0.

6. Observe: Click Play. How is the progress of the longitudinal waves shown on the

displacement graph? It is shown by the wave moving from left to right and back again.

7. Explore: Click Reset. Experiment with different values for the Strength and Freq. of the

tuning fork.

A. How does changing the strength of the fork’s vibration affect the characteristics of

the longitudinal wave? It adjusts the amplitude of the wave , The higher the

strength , the larger the wave’s amplitude is.

B. How does changing the frequency of the fork’s vibration affect the characteristics of

the longitudinal wave? It changes the speed of the wave moving , the stronger the

frequency, the faster it moves.