Waves, Sound, and Light 3차 미션

미르나래
|
2013-01-21

To be answered by 2/3 after reading chap2.2 and 2.3

Q1. An ambulance truck is heading for a wall 90m away. The sound wave of the siren bounces off the wall and comes back to the driver. The siren produces sounds at the frequency of 15/s, the truck is moving at 45m/s. What frequency of sound does the driver hear?(Aside from the wave that comes straight from the siren.)

Q2. Take a glass bowl or cup and tap it. (gently! I wouldn't be too rough with mom's special cup!) Try a little harder. Note the difference of the sounds. Try filling some water in the cup and see what happens.

annie0717
|
2013-02-03 20:40

1. This case is affected by the Doppler Effect, the theory invented by an Austrian scientist named Christian Doppler. The hypothesis is that the perceived pitch of a sound changes as the source of the sound moves toward or away from the hearer. When the source of the sound is closer to the hearer, the frequency, or the pitch, gets higher and vice versa. So I think the driver of the ambulance truck will hear a frequency of 3m/s. Since the sound bounces back, 45m/s divided by 15m/s is 3m/s.

2. The sound gets larger as we tap the glass bowl or cup harder. This is because intensity determines loudness. When the force of the sound wave is more intense, the sound grows larger. When we fill water in the bowl or cup, the pitch, or frequency of the sound will get lower. This is due to the fact that when there is water in the bowl or cup, the sound wave will not be able to travel as fast as it did when there was nothing except air, thus influencing the pitch or frequency of the sound.

alsxmthsu
|
2013-02-01 23:14

Q1)As the frequency gets higher the sound gets more louder and the contrast then the result will be it as well. When the siren comes near me then my ear will sense more louder sound and when the siren goes farther then ear will sense smaller sound and the frequecy will get loswer,

Q2)As we tap more harder the sounds gets larger and when we fill with more water then lower sound comes out compared for only a little water.

directioner
|
2013-02-01 18:39

A1. Well, the doppler effect is the change in preceived pitch that occurs when the source or the receiver of a sound is moving. So when the amblance truck is moving to the wall 90m away, and the sound waves bounces off the wall and comes to the driver, so when the truck gets closer to the wall, eventually the driver will hear more high sounds, I think. So the frequency sound that the driver hear might be 3dB?

A2. When you tap the glass a bit harder, the more energy a sound wave carries, and the intensity increases so the sound will be more loud. And if you fill some water in the cup, the more water you fill, the lower the sound gets.

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