why does the sound of an ambulance lower a tone when passing the house?

Question

speed of sound

Answer 1

It's because of the Doppler Effect. Sound is caused by waves in the air, and the shorter the waves, the higher the sound is. So imagine the ambulance sitting still behind your house and emitting waves. Now, picture what happens to the waves when the ambulance starts moving. It's still emitting the sound waves, but now the peaks are closer together because the ambulance has moved slightly closer to you between waves. The waves are getting pushed together.

Now, when the ambulance passes you, instead of moving toward you, now it's moving away. The waves appear longer, because the ambulance has moved a little farther away from you with each wave. They get pulled apart, creating longer wavelengths and lower sounds.

Answer 2

The Doppler effect. Coming towards you the sound is compressed by the speed of the vehicle,once the vehicle passes the sound is now "stretched out" due to the movement of the sound source away from you. The further apart the waves the lower the frequency or tone.

Answer 3

It is to do with the Doppler effect of perceived frequencies, and is also responsible for 'red shift' and 'blue shift' on planets, which is how we know whether they are travelling away from or towards the earth.

The best analysis is on Wikipedia (link below) "It is important to realize that the frequency of the sounds that the source emits does not actually change. To understand what happens, consider the following analogy. Someone throws one ball every second in a man's direction. Assume that balls travel with constant velocity. If the thrower is stationary, the man will receive one ball every second. However, if the thrower is moving towards the man, he will receive balls more frequently because the balls will be less spaced out. The converse is true if the thrower is moving away from the man. So it is actually the wavelength which is affected; as a consequence, the perceived frequency is also affected."

Answer 4

It's not a secrete that humans can not hear lower tones like other animals. For instants, An Elephant can be heard for 4 miles when they talk (not trumpeting) but the tones are so low, us humans can't hear the sounds without special equipment. When a siren is sounding off a mile away, we here the high tones of the siren, when it gets closer, we start to hear the lower tones thus, changing the tone and sounds of the siren when it approaches us.

Answer 5

It is based on the length of the sound wave that you here. As with a sub frequency sound you can't necessarily hear it at a close distance but you sure can feel it. You are actually hearing more of a blend of sound as the vehicle approaches and leaves. This is due to the different wave lengths of different sounds. Low frequencies have longer wave lengths and high frequencies have shorter wave lengths.

Answer 6

It's called the Doppler effect. Because you are listening to the sound from your "Fixed" point as it travels. If you were chasing the ambulance the sound would not change!!!

Answer 7

as the ambulance moves towards you the sound waves between you and the ambulence are getting squashed, so the wavelength changes (pitch). it is called the doppler effect, and is used to work out if and how fast planets are moving away from us.

Answer 8

The Doppler effect

Answer 9

Coming towards you the sound is compressed by the speed of the vehicle,once the vehicle passes the effect of the travel of the vehicle drags the sound wave

Answer 10

The Doppler effect.