I live in an apartment near the roads on the 17th level. I put my forehead on the window and I could feel the vibrations when the traffic light turned green and the cars and motorcycles started moving. How does that work?
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You know how water ripples outward when you drop something into it?
Vibrations are the same as that, except they’re typically a much higher frequency (the ripples are closer together).
They travel through air and matter all the same, though some materials are better at reducing them than others. Rubber and foam, for instance, have insulating properties that kind of kill vibrations instead of transmitting them. Steel and stone though are very good at transmitting them.
So, your building, made of steel and brick or concrete is perfect from absorbing the vibrations from street level and carrying them to you.
The source of it all is likely the motorcycle exhausts, since bikes tend to be louder and set at a higher frequency than typical cars. Though they all contribute to it somewhat.
On a city street, the noise gets ping-ponged back and forth from building to building, so it’s more concentrated than out in the open, which makes the vibrations a bit stronger than it would be otherwise.
Zooming way in, molecules move around and bounce into each other. In air that “bouncing” makes sound waves. In a solid like, the road or walls, it’s also a wave, but because the molecules are way tighter packed, the wave travels really fast.
Car engines do a lot of vibrating. The pistons go up and down really fast. So the engine shakes when it’s running. Part of that goes up into the air (sound), and part goes down through the tires into the road. Then that shaking force is making fast little “waves” that travel through the pavement and into the road and into the building.
But probably what you’re feeling on the window is mostly from the sound. The cars are vibrating, which makes waves of sound go through the air. Those sound waves are hitting your window, and makes the window shake (very small and fast shaking, you can’t see it).
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