Hi Guys,
Yes Nomad, that's right. With a large number of troops, or people, their combined steps could coincide with the resonant frequency of the bridge, causing it to sway, and eventually collapse!
See here, the Tacoma bridge
{Edit...} Hmmm, my Youtube input didn't work, so here is the link instead! Okay, it didn't, but putting the link in seems to do the same thing! I give up!
This was caused by the wind, but the principle is just the same.
Basically, resonance is the production of maximum amplitude by a short, minimum force.
There! Physics lessons do have some use!
Hope that helped,
James
CP Officer, and now Physics enthusiast! My teacher would be so proud!