The propagation time is from short to long 520m/s 1497m/s 340m/s ☆When the 100-meter race is held at the Games, the finish referee should keep track of the time when he sees the smoke from the gun. Exercise: ☆ There is a section of steel pipe with water in it, long L, knock it at one end and hear the sound 3 times at the other end. Under normal circumstances, the propagation speed of VM>V>V>V_ sound in air at 15☌ is 340m/s or 224km /h, the propagation speed in vacuum is 0m/s. The propagation speed of sound in the medium is referred to as the speed of sound. Exercise: (1) The experiment shown in P14 Figure 1-4 can conclude that vacuum cannot transmit sound, and there is no air on the moon, so astronauts who land on the moon must rely on wireless telephone conversations even if they are very close, because radio waves can also propagate in a vacuum, and the propagation speed of radio waves is 3x108m/s。 (2) "Wind, rain, reading, sound into the ears" description: gas, liquid, solid can make sound, air can transmit sound. In the air, sound propagates in the form of invisible sound waves, which reach the human ear, causing the eardrum to vibrate, and the person hears the sound. The transmission of sound requires a medium, and vacuum cannot transmit sound. (3) Knocking on the table, hearing the sound, but not seeing the vibration of the table, what way can you come up to prove the vibration of the table? Sprinkle scraps of paper on the table, which will jump when you hit the table. (2) In the lyrics of the "Yellow River Cantata", "the wind is roaring, the horse is howling, and the Yellow River is roaring", the sound sources of "roar", "call" and "roar" here are air, horses, and Yellow River water. Exercises: (1) People speak, sing by the vibration of the vocal cords, gentle birdsong by the vibration of the song membrane, crisp cricket calls by the vibration of wing friction, the vibration frequency must be between 20-20,000 times / second. A vibrating object is called a sound source. When you press and hold the pronounced tuning fork with your hand, the pronunciation stops, indicating that the vibration stops and the sound stops. The phenomenon of Figure 1-1 of textbook P13 shows that all sounding objects are vibrating.
"Sound Phenomena" test volume First, the occurrence and propagation of sound 1.
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