earthquake

[jacklyn.le2472]

A building in an earthquake sway back and forth with gradually increasing amplitude until a collapse finally occurs. This is an example of:
a) destructive interference
b)the Doppler effect
c) resonance
d) Young's modulus.


answer is (c).


I get why it's not b and d. I thought it would be a, but why resonance?!?!?!?

[mcat_premed3832]

That was a well designed multiple choice question because answer choice A made you think about "destructive" as relating to the building and the earthquake. However, destructive interference would have quite the opposite effect!

For example, complete destructive interference is when waves that are exactly out of phase sum to create no waves at all. So you can imagine a system (similar things exist) that has noise coming from one speaker at a loud volume and another speaker screaming back noise at a loud volume but opposite phase: what do you hear? Nothing. Noise cancellation.

One of the legends engineers tell about their graduation ring is that it was forged from a huge bridge that collapsed generations ago due to a resonant signal (either generated from wind notes created through the bridge or a smoke stack down the river). It is the reason for massive testing of superstructures (wind tunnels, using different materials with different resonance instead, like the bridge at that time, being made of just one pure material).

Anyway, you could have thought of the opera singer hitting a note, resonates, and shatters the crystal glass. Resonance, amplitude and energy are related as described in PHY 7.1.4 in the GS text. Or if you don't have a physics background, you can go to the following link which goes step by step: www.cpo.com/ipcres/pdfs/unit4/ch12sec3.pdf