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Movement of Sound

  • Introduction
  • Video & Results
  • Materials
  • Procedure
  • Preparation & Notes
  • Download Files

Activities that Explore Movement of Sound

  1. Sound travel requires a medium - Sound waves need a gas (air), liquid or solid to travel. There is no sound in a vaccum. This demonstration uses compression waves to blow out a candle.

  2. Gas vs. Solid - Students compare the efficiency of sound of a ticking watch travelling through bags of air and bags of flour.

  3. Directing Sound through a Solid - Students will experience the amplification of sound when it travels in a directed fashion through wire hangers and string.

  4. Sound traveling through a liquid - Students will use a stethoscope to hear sounds created by a tuning fork traveling through gas (air) and a liquid (water).

 

Movement of Sound through Gases, Liquids & Solids

Sound is vibration that moves through a gas, liquid or solid and can be detected by an animal. The movement of sound requires a medium. Sound waves are also described as mechanical longitudinal waves and compression waves. The speed of sound is dependent upon the medium through which it travels. Because the molecules are closest together in solids, sound generally travels through solids faster than liquids and gases.baggie

In gases, the molecules are more disperse with greater spaces between them. For this reason, sound travels through gases slower than both liquids and solids. The table below lists the speed of sound through several gases, liquids & solids.

Speed of Sound in Gases, Liquids and Solids
Substance
meters/sec
miles/hours
vacuum
0 0
carbon dioxide
270 604
air
340 760
hydrogen
1,320 2,950
water
1,470 3,290
glass
5,000 11,180
iron
5,120 11,450

 

 

1. Demonstraton of the milk jug activity


Animation of a longitudinal wave (wave_animation).

2. Solid vs. Gas: Sound travelling through a solid

Baggies

Sound is created by compression waves. Vibrations created in one location travel by creating vibrations in neighboring particles. Solids have particles (molecules) packed very close together. Gases are more diffuse with molecules not interacting very much. For this reason, sound travels more efficiently through solids because particles are more tightly packed. When holding up the baggies next to ears, it is easier to hear the ticking watch through a solid. This exercise can be difficult in a noisy classroom but sometimes works best when the students can hear through the solid but can't hear through the baggie filled with air.

baggie

3. Directing Sound through a Solid

air_vibration (Left) When the hanger is tapped with the fingers out of the ear, the sound spreads in all directions through string_vibrationair (a gas). A smaller percentage of the sound waves are captured by the ears. The noise is not very loud.

(Right) When students put their fingers in their ear and listen for the sound of the tapped wire hanger, it sounds like a gong and is much louder. With fingers in the ears, the sound travels through the solid hanger and string. It's directed toward the ear and travels through solid more efficiently.

When the hanger is positioned on the string off-center, the sound is detected primarily to one ear. The one that has the shorter end of the string.

4. Liquid vs. Air: Sound travelling through a liquid

stethoscopeThe tuning fork will be louder when the stethoscope diaphragm is held under the water. This result demonstrates that sound travels more efficiently through a liquid than a gas.


Materials
1. Air as a medium for sound
candle_still

  • candle
  • matches or lighter
  • empty plastic 1 gallon milk jug
  • wooden serving spoon

 

2 & 3. Air vs. Solid: Sound travelling through a solidhanger

  • plastic baggie filled with air
  • plastic baggie filled with a solid (flour, sand or sugar)
  • ticking watch
  • wire hanger
  • string (we used fishing line)
  • wooden or metal spoon

4. Air vs. Liquid?

  • bowl of water
  • stethoscope
  • tuning fork & striker (or dense but soft object)
  • alcohol wipes

 

1. Air as a medium for soundmilkjug

  1. Have an adult light the candle in a location free from breezes.
  2. Hold the milk jug 8-12 inches from the flame with the opening of the jug aimed at it.
  3. Strike the back of the milk jug with the wooden spoon.

Was the flame extinguished? Look at the animation of a longitudinal wave and describe what you think happened.

 

2. Air vs. Solid: Sound traveling through a solid

Bag of Air vs. Bag of Solid

  1. Press a plastic baggie filled with air against your ear with the back side of ticking watch pressed on the side.
  2. Listen for the watch ticking. Can you hear it?
  3. Now hold a plastic baggie filled with flour against your ear with the ticking watch again. Can you hear it? Which baggie could you hear better with?

3. Directing sound travel through a solid

Wire Hangers

    hangar smll
  1. Tie the middle of the string to the hook on the wire hanger.
  2. Wind the string around the end of your index fingers on each hand.
  3. Have someone tap the hanger while it hangs freely and listen to the sound. Do not let the hanger touch your body when tapped. This will dampen the sound vibrations.
  4. Place your index fingers in your ear and have someone tap the hanger with the spoons while it hangs freely.

What is the difference in the sound? Can you come up with an explanation for the difference?
Variation: Move the hanger to a place on the string that is off-center and repeat the tapping with fingers in your ears. How does this change what you hear?

 

4. Gas vs. Liquid

stethoscope
  1. Put the stethoscope in your ears.
  2. Have a partner strike a tuning fork and touch the end to the bowl.
  3. Listen through the stethoscope with the diaphragm in the water and out of the water.

Where is the diaphragm louder? In the water or out of the water?


Notes

  1. Students love the milk jug candle flame activity. Be sure to explain safety precautions regarding the open flame to the students before the milk jug activity.
  2. The hanger - finger in the ear exercise is surprisingly dramatic, inexpensive and simple. No need to tap the hanger very hard. Make sure that it is not touching anything so vibrations aren't dampened. Also make sure the kids have their fingers in their ear.

References

  1. Robert Gardner. (2006) Jazzy Science Projects with Sound & Music. Enslow Publishers, Inc. Berkeley Heights, NJ. (http://www.enslow.com)

Downloadable files

Handouts with instructions for the event. (pdf)