![]() ![]() Vertical temperature gradients can cause sound to either refract away from the ground (when warm air near the ground is beneath cooler air above) or towards the ground (when cool air near the ground is trapped by a layer of warm air above, i.e., an inversion). Wind may cause sounds to be louder downwind, since the molecules through which sound waves propagate are being moved downwind, instead of spreading out equally in all three dimensions. More importantly, wind and temperature can significantly affect how sound waves travel. A substantial change in atmospheric pressure, equivalent to thousands of feet of elevation gain, has a small influence on noise level for most sources, but substantially affects the received levels of those sounds. Lower humidity absorbs more sound, especially at higher frequencies, because of "molecular relaxation" in the gases in the air (a level of 10% humidity absorbs the most). Effects of Atmospheric ConditionsĪtmospheric absorption of sound varies with environmental conditions such as relative humidity, atmospheric pressure, temperature, and wind. Noise levels of 50 dB at night increase cortisol (a stress hormone) production which causes arteries to constrict and elevates blood pressure. Road noise has been shown to constrict arteries and elevate blood pressure. Other complications include possible immune system changes and birth defects. Loud or prolonged sounds have been shown to cause hearing impairment, hypertension, sleep disturbance, annoyance, and ischemic heart disease (heart disease linked to reduced blood flow to the heart). Studies have also shown that low frequency noise in the oceans, largely related to increased commercial shipping, has increased by as much as 10 dB since the 1960s. Sound travels much faster and farther underwater, which means a noise source can have a much greater radius of impact than it would have on land. Noise definitely affects aquatic environments. Noise also "stresses" wildlife making them less resistant to disease. Gleaning bats (those that pluck insects from leaves) will not hunt in noisy areas. Chinese frogs have even shifted their calls to the ultrasonic range (above the frequencies humans can hear) so they can locate each other during mating season. Other birds may just sing louder in noisy areas. Because female birds of certain species prefer males singing at a lower pitch since it denotes maturity, this may lead to reduced bird populations. Some birds sing at a higher pitch in noisier areas. For example, extra sounds cause "auditory masking" which reduces an animal's ability to detect communications and predators. "Noise" is any unwanted sound or extraneous sounds (sound without any function). It is also better adapted to measuring hearing damage and speech interference in humans. The dBA scale has a filter so the sound level meter is less sensitive to low and high frequency sounds just like human hearing. Humans are particularly sensitive to sounds ranging in frequency between 20 Hertz. A whisper is between 20 and 30 dB, noisy conversation is about 50 dB, a vacuum cleaner is about 70 dB, a lawn mower is about 90 dB and a car horn at 1 m is about 110 dB. The threshold of pain for humans is 1 Watt per meter squared and corresponds to 120 dB. 0000000000001 watts per meter squared and corresponds to 0 decibels. The threshold of human hearing has an intensity of about. The loudness of a sound relates the intensity of any given sound to the intensity at the threshold of hearing. The intensity of a sound is the power of the sound in Watts divided by the area the sound covers in square meters. Classroom teacher Lynette Cummings developed the activities as part of the Teacher to Ranger to Teacher Program. Using data like intensity readings and spectrograms, and simple techniques like listening to and identifying sounds, students research how sounds affect people and the environment. They learn how to measure intensity and loudness, the difference between sound and noise, and when a sound is considered noise pollution. Through this multi-part activity, students learn about the properties of sound waves, particularly sound intensity and loudness. Grade Level: High School: Ninth Grade through Twelfth Grade Subject: Science State Standards: Iowa Core: SS.9–12.H.1, 21.9–12.TL.3, 21.9–12.TL.4, 21.9–12.TL.5 Next Generation Science Standards: PS4 Wave Properties ![]()
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