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Title: Sound wave travel through different properties of matter & changing direction of sound
Principle(s) Investigated: Sound waves, longitudinal and transverse waves, properties of matter, speed of sound
Standards : Physics - Waves
4. Waves have characteristics properties that do not depend on the type of wave. As a basis for understanding this concept:
a. Students know waves carry energy from one place to another.
b. Students know how to identify transverse and longitudinal waves in mechanical media, such as springs and ropes, and on the earth (seismic waves).
c. Students know how to solve problems involving wavelength, frequency, and wave speed.
d. Students know sound is a longitudinal wave whose speed depends on the properties of the medium in which it propagates.
Materials:
- Demonstration of sound wave travel
- Springs
- Travel of sound through various phases of matter
- Ziplocs
- Water
- Book, sand/dirt
- Fish bowl, stem cup
- Bouncing sound
- Cardboard tubes, paper tubes
- Sound-reflecting/sound-absorbing materials
- Cardboard, plastic, aluminum foil, ceramic tiles, cork, egg cartons)
Procedure:
Travel of sound through various phases of matter:
- Put sand or dirt in a ziploc bag so that is about half full. Push the extra air out and then seal it so that no sand or dirt will leak out.
- Fill another ziploc bag with water so that is as full as the bag of dirt. Push the extra air out and then seal it so that no water will leak out.
- Blow air into another ziploc bag so that it is inflated. Let some air out until the bag is as full as the bags of the dirt and water. Seal it so that no air will leak out.
- Clear off the table and place the bags on the table.
- Put one ear gently on the bag and put your finger in your other ear.
- Lightly tap or rub the table with a wooden stick from about an arm's length away.
- How well can you hear the sound?
- Lift your ear off the bag and tap or rub the stick again on the table.
- Do you hear it better with or without the bag?
- Repeat Step 5-7 with the other two bags.
Bouncing Sound
- Arrange two cardboard tubes on a table so that they are at right angles to each other.
- Place a sound device (e.g., clock, watch) at the end of one tube.
- Put your ear close to the end of the other.
- Can you hear the tick of the clock?
- Repeat the test with squares of other materials that the sound can bounce off of.
- How does the loudness of the tick compare to the first test?
- Which material is the best sound reflector?
Student prior knowledge: Properties of matter (solid, liquid, gas), longitudinal and transverse waves
Explanation:
Sound is a mechanical wave that is an oscillation of pressure transmitted through a solid, liquid, or gas, composed of frequencies within the range of hearing. Sound waves may not be seen everyday by the naked eye; however, we are able to make changes to sound waves that help us understand that they are physical properties.The mechanical vibrations that can be interpreted as sound are able to travel through all forms of matter: gases, liquid, solids, and plasmas. The matter that supports the sound is called a medium. Sound cannot travel through a vacuum; at least, it cannot be heard.
Sound is transmitted through gases, plasma, and liquids as longitudinal waves (compression waves). Through solid, however, it can be transmitted as both longitudinal and transverse waves. Longitudinal sound waves are waves of alternating pressure deviations from the equilibrium pressure, causing local regions of compression, while transverse waves (in solids) are waves of alternating shear stress at right angle to the direction of propagation.Matter in the medium is periodically displaced by a sound wave, and thus oscillates. The energy carried by the sound wave converts back and forth between the potential energy of the extra compression (in case of longitudinal waves) or lateral displacement strain (in case of transverse waves) of the matter and the kinetic energy of the oscillations of the medium.
Sound waves are often simplified to a description in terms of sinusoidal plan waves, which are characterized by these generic properties: frequency, wavelength, wavenumber, amplitude, sound pressure, sound intensity, speed of sound, and direction. Sometimes speed and direction are combined as a velocity vector; wavenumber are direction combined as a wave vector.
The speed of sound depends on the medium the waves pass through, and is a fundamental property of the material. In general, the speed of sound is proportional to the square root of the ratio of the elastic modulus (stiffness) of the medium to its density. Those physical properties and the speed of sound change with ambient conditions. For example, the speed of sound in gases depends on temperature. In 20 degrees Celsius (68 degrees Farenheit) air at sea level, the speed of sound is approximately 343 m/s (767 mph). In fresh water, also at 20 degrees Celsius, the speed of sound is approximately 1,482 m/s (3,315 mph).
Questions & Answers:
1. Does sound travel in a straight line?
When a person is talking and you stand behind them, are you still able to hear their voice and the words they are saying? Yes, we are able to. This tells us that sound waves do not travel in one straight line and direction, but it is like a ripple in a water. Refer to the videos in the bottom of the page.
2. Why does a person's voice seem to change when you are further away from the person or at a different angle?
Some frequencies of sound waves are able to travel further than other frequencies. For example, higher frequencies travel at a quicker rate while lower frequencies take longer to travel the same difference. The energy of the sound wave is able to carry the lower frequencies further, making the person's voice sound deeper. Actually, you are hearing the lower frequencies of their voice.
3. Through what property of matter (solid, liquid, gas) can you hear sound better? Why?
Sound waves can be heard best when the sound waves travel through solids because of the condensed and compact area of the object. When sound waves travel through the atmosphere (gas), it must travel the vast space of molecules in the atmosphere. However when sound waves travel through a solid, the sound waves travel through the whole object, then creating a vibration.
Applications to Everyday Life:
1. How can you hear things approaching you?
2. Make your own speakers.
3. Freeway Walls
People who lived on the Great Plains in the early days of the United States put an ear on the ground to tell if buffalo or horses were coming. What may be their reason to do this? As seen in the Lion King video, we can see the rocks rumble on the ground before Simba hears the stampeded through the canyon.
DIY: Make your own iPod speaker
You can use household items to reflect sound waves in a narrower space and direct the sound waves so it sounds louder. From personal experience, I place my iPhone in my car cup holder and am able to hear the person on the other line louder because the sound waves reflect in a narrow space and moves air towards a specific direction.
Why are there walls present on a freeway when it cuts through a neighborhood? It is to help alleviate the noise (excessive sound) from cars that will leak into the neighborhoods. For neighborhoods near airport, there have been many issues with the noise of airplanes flying overhead.
Apple Applications:
The following applications are free at the Apple Store:
Decibel - This is an application that can measure the decibel levels of the current environment.
Signal Generator - This is an application that can generate different sound signals at different frequencies and ranges.
Videos:
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