Re: Midterm Question - Sort of

[Leigh Palmer <palmer@SFU.CA>]

> My gut feel is that you can't look at this as anything but impulse
> excitation, because you're not providing a sinusoidal or even a square wave
> input at all. To do so, you'd have to pull on the swing as well.

Fourier's theorem would say you're wrong. There is a DC term
if you only push, of course, but that doesn't matter.

On a related topic: It always bothers me when the Tacoma
Narrows Bridge collapse is cited as an example of resonance.
It's not. The wind was steady, more or less, and there was
no significant component at the bridge's resonant frequency.
It is a case of nearly pure DC excitation.

It's a great film, but it's an example of aeolian excitation,
like blowing on a taut piece of grass between your thumbs.
I have many good demonstrations of resonance. Using the
Tacoma Narrows Bridge as an "example" can only obscure the
concept in the mind of a student.

Leigh