Driving past cars at rest

[psi20]

When you drive past cars that are at rest, you hear something. It sounds as if the car is driving past you. Is that the doppler effect? Or is it something else? Why does it happen? The car isn't making any sounds but going past it you can hear a sound.

[TimeTraveler]

Here is a link: http://informationcentre.tripod.com/facts/waves.html

 

THis part should answer your question:

 

There's one last cool thing about sound waves and that is the Doppler Effect. Picture yourself in a car driving towards another car. You're each going 10 mph, but relative to you that other car is approaching at 20mph! It's the same thing with sound waves. If you are moving toward the source of some sound waves, then they are going to sound different. Why? Let's say that the waves are moving unrealistically slow. Frequency is one wave per 10 seconds. Wavelength is ten meters. That means the speed of the waves is 1 meter per second. If you start moving toward the source of the sound waves, however, relative to you the waves will be travelling 2 meters per second. Remember, speed = wavelength x frequency. If the speed doubles, but wavelength remains the same, then frequency has to double. It makes sense; the frequency you'll see is 1 wave per 5 seconds or 2 waves per 10 seconds since you're moving toward them now. Now, you see that when you move toward the sound source or the sound source moves toward you, the frequency increases. Likewise, if you move away from the source or the source moves away from you, the frequency decreases. You can test this for yourself by standing by a road. Listen to a car as it is approaching you. The pitch will be getting higher until it crescendos as it reaches you. Then the pitch will drop away as the car leaves you. This is the doppler effect. The doppler effect works for light also.

[jsatan]

your sound bouncing off the car.

[swansont]

When you drive past cars that are at rest, you hear something. It sounds as if the car is driving past you. Is that the doppler effect? Or is it something else? Why does it happen? The car isn't making any sounds but going past it you can hear a sound.

 

It's the disruption of the air as you drive by.

[mossoi]

It's the sound of your engine being reflected back off the stationary car.

[drz]

yup.

 

Now, you want a crazy expieriance, get on a 250 lb motorcycle and drive by a semi moving around 70 mph. It creates a vacuum effect that pulls you near the truck. Good fun.

 

Its much the same as when you are driving beside concrete barriers, they reflect the sound of your vehicle, the wind, etc. Also, as you are moving down the road, there is a bubble around your car (so to speak) from the displaced atmoshpere. This could also be the sound you hear as you pass by a parked car.