TERRESTRIAL S Noise Barriers

Transcription

1 TERRESTRIAL S Noise Barriers INTRODUCTION Materials have different rates of absorbing or reflecting sound. Typically flat, hard, or high density surfaces reflect sound where soft, fluffy, and low density materials absorb sound - like the bark of a redwood tree in Muir Woods National Park. Hard, flat, dense surfaces like rock will block sound, but it can also reflect the sound into another area or back in the direction it came, impacting the area again. Low frequency or low pitch sounds have longer wavelengths and can be heard over a much longer distance than high frequency, short wave sounds. High pitch sound is absorbed by small things like leaves, grass, etc. There are fewer objects or natural life forms (i.e., trees, plants, etc.) large enough to absorb long wavelengths. Sound absorption converts the energy of sound into heat. The heat generated is so small that people cannot feel it. Air temperature and wind speeds also affect sound. Humans can hear as low as 0 db (db = decibels). A normal speaking voice is under 60 db. Vacuum cleaner is ~70 db. Rock concerts are ~125 db which is also the human pain threshold. A typical suburban area is 50 to 60 db. The crater of Haleakala National Park is 10 db. Grand Canyon National Park is 20 db (softer than a whisper) except when aircraft noise intrudes. People and animals begin to have hearing loss, raised stress hormone levels, and hypertension at db. Traffic noise commonly ranges from 70 to 80 db 50 feet (15 m) from a highway (federal highway administration publications/publicroads/03jul/06.cfm) The image below illustrates the concepts of frequency and amplitude. The magenta wave has one half the amplitude of the black wave and produces a quieter sound. The green wave completes half as many cycles as the black wave, meaning its frequency is one half the black wave and has a lower pitch. OBJECTIVES To design a noise barrier to reduce the impact of noise on the environment. To utilize scientific method to test materials and design for the best solution to reduce noise. To gain an experiential understanding of sound waves and energy transfer NEXT GENERATION SCIENCE STANDARDS Kindergarten K-ESS-1, K-ESS3-3 Grade 1 K-2-ETS1-1, K-2-ETS1-2, K-2-ETS1-3 Grade 2 2-PS1-1, 2-PS1-2, 2-PS1-3, K-2-ETS1-1,K-2-ETS1-2, K-2-ETS1-3 Grade 3 3-LS4-4, 3-5-ETS1-1, 3-5-ETS1-2, 3-5-ETS1-3 Grade 4 4-PS3-1, 4-PS3-3, 4-PS3-4, 4-ESS3-1 Grade 5 5-ESS3-1, 3-5-ETS1-1, 3-5-ETS1-2, 3-5-ETS1-3 Middle School MS-PS2-5, MS-PS3-3, MS-PS4-1, MS-PS4-2, MS-LS1-5, MS-LS1-2, MS-LS2-4, MS-LS2-5, MS-LS4-5, MS-ESS3-3, MS-ESS3-4, MS-ETS1-1, MS-ETS1-2, MS-ETS1-3, MS-ETS1-4

2 TERRESTRIAL S Noise Barriers N ACTIVITY INTRODUCTION When a barrier quiets a loud noise or reduces the loudness or amplitude, the barrier is absorbing the sound s energy. In this exercise, we will experiment with different materials and test to see if natural or man-made materials are more effective in absorbing sound. Depending on what materials you have available, you can have one group use only natural materials, another group use only man made, and another can use both. If you are wanting to reduce the impacts of noise, determine if it is better to absorb or reflect the energy. One type of barrier that can be done with natural materials and a lot of elbow grease is called a hugelkulture. Builders often plant a garden or native plants to hold the soil together. KEY DEFINITIONS Amplitude: the relative strength of sound waves (transmitted vibrations) and can be detected by hearing organs, which we perceive as loudness or volume. Decibels: (db) refers to the sound pressure level or intensity; amplitude is measured in db. Frequency (pitch): defined as the number of times per second that a sound pressure wave repeats itself and is expressed in terms of hertz (Hz).

3 TERRESTRIAL SO N Activity - Noise Barriers ACTIVITY INSTRUCTIONS Location Materials Outside Natural materials (found outdoors) Recyclables (egg cartons, cardboard, etc.) Other possible materials: cloth Noise meter Preparation Have students research materials used to reduce noise before they design their barrier. Instructions The students will have a contest to make the best noise barrier. Use the noise meter app to record the effectiveness of the noise barrier by measuring decibels of the same sound on both sides of the barrier. Do this with different noise makers of varying pitch. For best results, do multiple tests for each noise maker. Results and Discussion Which materials do you think worked best? Did the noise barriers work the same with different pitches? If you could do it again, with unlimited materials, what would you create? Also, would your noise barrier reduce the impact of noise for wildlife? Would animals that avoided the noise return? How would this affect wildlife's offspring? Gas powered machines like cars, lawn mowers, airplanes and boats are a major source of today's noise pollution. How else does oil and gas consumption affect the Earth and you? What are the pros and cons of the noise barrier you created? Benefit Examples Reduces noise Easy to make ustainable materials Inexpensive turdy to withstand the elements an be used by animals (i.e. tree branches) ultiple purpose use (i.e. If the barrier is made of wood, you could paint a community mural on it.) ecycling materials that would otherwise go in the trash Con Examples ot effective in reducing noise E pensive Toxins would potentially leak into ground (plastics, tires) Will degrade quickly Not visually appealing Unsustainable materials Barrier needs to be large to be effective

4 TERRESTRIAL SOUND Noise Barriers Worksheet Page 1 Instrument Making Noise (hands, metal, whistle, etc.) Type of Noise Created (low pitch, high pitch, etc.) Hypothesis: (Example: The barrier made from stone will reduce the noise more than the barrier made from paper.) Describe your noise barrier. Draw your noise barrier in the space below.

5 TERRESTRIAL S Noise Barriers Worksheet Page 2 When the barrier makes a loud noise quieter or reduces the loudness or amplitude, the barrier is absorbing the sound s energy. A tiny amount of heat is transferred to the barrier that is too small for us to feel. Test 1: Distance between noise makers and barrier weather Instrument(s) used Results: Decibels in front of barrier for each instrument and rate the sound (loud, medium, quiet): Decibels behind barrier for each instrument and rate the sound (loud, medium, quiet): Either alter Barrier #1 OR make and test another barrier. Test 2: Distance between noise makers and barrier weather Instrument(s) used Results: Decibels in front of barrier for each instrument and rate the sound (loud, medium, quiet): Decibels behind barrier for each instrument and rate the sound (loud, medium, quiet): Either alter Barrier #2 OR make and test another barrier. Test 3: Distance between noise makers and barrier weather Instrument(s) used Results: Decibels in front of barrier for each instrument and rate the sound (loud, medium, quiet): Decibels behind barrier for each instrument and rate the sound (loud, medium, quiet):

6 TERRESTRIAL S s Worksheet 3 Summarize your results and state your conclusion. (Example: The lowest db was behind barrier #1. I think it was most effective because of its thick wood wall.) Would your noise barrier successfully reduce the impact of noise for wildlife? Would the animals that avoided the noise return? How would this affect wildlife offspring? Gas powered machines like cars, lawn mowers, airplanes and boats are a major source of today's noise pollution. How else does oil and gas consumption affect the Earth and you? If you reduce noise from gas powered machines, what else would benefit?