A bridge can start to vibrate for many reasons: wind loading and vehicle or even foot traffic. Do you know these vibrations can totally destroy a bridge?
Have you ever wondered why strong bass music is so exciting? You feel like your whole body is shaking with it. Is it because of the magic of the music?
It turns out it’s not magic that wind can make a bridge fail or that a talented musician can create music that moves you so strongly. The trick here is resonance. Every object, whether it’s a bridge or the human body, has its own series of natural frequencies. Once an external excitation matches a natural frequency of an object, resonance will occur. When the wind loading frequency reaches the natural frequency of the bridge, it breaks. When the subwoofer speaker produces music that matches the natural frequency of a human lung, people feel the vibration in their chests. That’s the magic of bass music.
The question becomes how can we find the natural frequencies of an object so that we can create or avoid resonance? In solid mechanics, 99% of the time we want to avoid resonance to protect the structure. Modal analysis is the answer here.
Here are the accompanying handout slides for this lesson.