# what's wrong with my basic math and/or physics? **URL:** \ **Category:** Factual Questions\ **Created:** [May 7, 2004, 6:14pm UTC](https://boards.straightdope.com/t/whats-wrong-with-my-basic-math-and-or-physics/244046 "2004-05-07T18:14:21Z")\ **Posts on this page:** 7\ **Page:** 2
**Author:** ![MonkeyMensch](https://avatars.discourse-cdn.com/v4/letter/m/82dd89/32.png) [@MonkeyMensch](https://boards.straightdope.com/u/MonkeyMensch)\ **Post date:** [May 8, 2004, 6:18pm UTC](https://boards.straightdope.com/t/whats-wrong-with-my-basic-math-and-or-physics/244046/21 "2004-05-08T18:18:52Z")
I’m going to build this thing! I remember as a child watching the Foucault pendulum at the San Diego Museum of Natural History swing back and forth and having to wait _forever_ to see it knock down the next wooden peg. The wooden pegs, of course, marked the pendulum’s progress as its plane of rotation turned underneath the Earth’s motion. So with this bad boy they’re will be no waiting! With a period of 60 seconds and an swing amplitude of say 10 degrees, not that it matters, we get to see pegs knocked over on every swing that are spaced **1 meter** apart! Granted they might have to be tall pegs, but I’m going to Home Depot right now! Who’s with me? ---
**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\ **Post date:** [May 8, 2004, 6:43pm UTC](https://boards.straightdope.com/t/whats-wrong-with-my-basic-math-and-or-physics/244046/22 "2004-05-08T18:43:25Z")
> [@MonkeyMensch](#): > > I’m going to build this thing!.. Who’s with me? You’re buying, right? 😉 ---
**Author:** ![Omphaloskeptic](https://avatars.discourse-cdn.com/v4/letter/o/bcef8e/32.png) [@Omphaloskeptic](https://boards.straightdope.com/u/Omphaloskeptic)\ **Post date:** [May 8, 2004, 8:55pm UTC](https://boards.straightdope.com/t/whats-wrong-with-my-basic-math-and-or-physics/244046/23 "2004-05-08T20:55:47Z")
If you want a long-period pendulum without building a kilometer-high building you can build a compound pendulum: a rod with weights on both ends, suspended from a point near the center of mass. These have much longer periods than a simple pendulum of the same length. ---
**Author:** ![wisernow](https://avatars.discourse-cdn.com/v4/letter/w/13edae/32.png) [@wisernow](https://boards.straightdope.com/u/wisernow)\ **Post date:** [May 8, 2004, 10:05pm UTC](https://boards.straightdope.com/t/whats-wrong-with-my-basic-math-and-or-physics/244046/24 "2004-05-08T22:05:33Z")
> [@Xema](#): > > I don’t see how 142 km comes into this. :smack: :smack: :smack: :smack: My mistake guys! I must have been drinking. I used the formula for area pi r sq instead of 2 pi r! Sorry! :smack: :smack: :smack: > [@zut](#): > > What **Xema** said. 467 meters. :smack: :smack: My apologies! :smack: :smack: ---
**Author:** ![MonkeyMensch](https://avatars.discourse-cdn.com/v4/letter/m/82dd89/32.png) [@MonkeyMensch](https://boards.straightdope.com/u/MonkeyMensch)\ **Post date:** [May 9, 2004, 10:11am UTC](https://boards.straightdope.com/t/whats-wrong-with-my-basic-math-and-or-physics/244046/25 "2004-05-09T10:11:55Z")
> [@Omphaloskeptic](#): > > If you want a long-period pendulum without building a kilometer-high building you can build a compound pendulum: a rod with weights on both ends, suspended from a point near the center of mass. These have much longer periods than a simple pendulum of the same length. I find your ideas intriguing and wish to suscribe to your newsletter. Are you describing a single rigid rod with the CM near the pivot point or a set of rods with connected pivots? Do tell… ---
**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\ **Post date:** [May 9, 2004, 1:53pm UTC](https://boards.straightdope.com/t/whats-wrong-with-my-basic-math-and-or-physics/244046/26 "2004-05-09T13:53:10Z")
> [@MonkeyMensch](#): > > IAre you describing a single rigid rod with the CM near the pivot point or a set of rods with connected pivots? Do tell… The former. If you’ve ever used a triple-beam balance and observed its motion as it settles down on a reading, you know how short the period is relative to the beam length compared to a pendulum of similar dimensions. Same idea. ---
**Author:** ![moriah](https://avatars.discourse-cdn.com/v4/letter/m/b2d939/32.png) [@moriah](https://boards.straightdope.com/u/moriah)\ **Post date:** [May 9, 2004, 10:24pm UTC](https://boards.straightdope.com/t/whats-wrong-with-my-basic-math-and-or-physics/244046/27 "2004-05-09T22:24:51Z")
Pulling back this hypothetical mass to a thirty degree declension and letting go would create a one minute period. Traveling speed would be an average of two miles/min (120 ml/hr). OK calc majors, what would it’s maximum speed actually be at the nadir of the arc? But it would also take a full minute period if you pulled the mass back just 3 inches. Imagine how painfully slowly the mass would move then (one foot/min, actually). Boggling. Peace. [Previous page](https://boards.straightdope.com/t/whats-wrong-with-my-basic-math-and-or-physics/244046.md?page=1)