Go Back   Steve's Digicams Forums > Post Your Photos > Biweekly Shoot Out

Reply
 
Thread Tools Search this Thread
Old Mar 3, 2006, 9:16 AM   #1
Moderator
 
calr's Avatar
 
Join Date: Sep 2003
Location: Beaverton, OR
Posts: 8,466
Default

Here is a clock at the Portland Convention Center. There are other similar clocks at some observatories around the country.

The large metal ball is suspended on a thin cable from a point about 40-50 feet above. It swings back and forth the width of the brass circle containing the small disks and rods. As the earth rotates, the angle of the pendulum swing relative to ring of small disks rotates and somehow the ball strikes each of the small disks in succession and tips it over. This causes the rod below it to swing up parallel to the floor and point to the center of the circle. The circle of disks represents one full day. I don't know how the disks are reset or exactly how the ball contacts the disks. Maybe some astrophysicist out there can explain it better.

Here are two views of the "device", one from above and one below.





Cal

calr is offline   Reply With Quote
Sponsored Links
Old Mar 3, 2006, 11:14 AM   #2
Senior Member
 
Join Date: Jul 2005
Posts: 2,885
Default

I love things like this...how cool is that!!I wonder how someone ever came up with that idea and then actually got it to work! Very cool feat of engineering.
vsch1 is offline   Reply With Quote
Old Mar 3, 2006, 11:37 AM   #3
Senior Member
 
Join Date: Sep 2005
Posts: 1,093
Default

vsch1 wrote:
Quote:
I love things like this...how cool is that!!I wonder how someone ever came up with that idea and then actually got it to work! Very cool feat of engineering.
Since you were foolish enough to ask: it is explained here:

http://visite.artsetmetiers.free.fr/..._museum_a.html

This was a famous experiment by the renowned French physicist Foucault. As to the photo,I agree that the clock is fascinating, but would prefer to see an angle or point on the sweep of the ball that highlighted the function a bit more. Maybe it's just the benighted engineer in me...


tclune is offline   Reply With Quote
Old Mar 3, 2006, 12:33 PM   #4
Moderator
 
calr's Avatar
 
Join Date: Sep 2003
Location: Beaverton, OR
Posts: 8,466
Default

Although I have seen this pendulum clock many times, I have never seen what happens when one of the disks is flipped. I have seen it when some of the disks were flipped and the rest were upright as you see in the photos. I know there is a simular pendulum at the Grifith Park Observatory in Los Angeles. At that location, they set up wood pegs or blocks around the circle and the pendulum knocks them over. I will do some research and try to determine how this pendulum interacts with the disks and how they are reset.

Cal

calr is offline   Reply With Quote
Old Mar 3, 2006, 12:44 PM   #5
Moderator
 
selvin's Avatar
 
Join Date: Aug 2002
Posts: 7,204
Default

Undoubtedly meets the challenge.

The first example of the Foucault pendulum I saw was at the Museum of Science and Industry in Chicago. Where as a young college student in engineering I was totally fascinated by the whole concept and watched it at intervals for several hours.

I visited tclune's URL recommendation and could not get the English version to work. An english explanation of the whole principle can be found at the University of New South Wales site:

http://www.phys.unsw.edu.au/PHYSICS_..._pendulum.html

Cheers
selvin is offline   Reply With Quote
Old Mar 3, 2006, 1:01 PM   #6
Moderator
 
calr's Avatar
 
Join Date: Sep 2003
Location: Beaverton, OR
Posts: 8,466
Default

I found several references to the Portland Foucault Pendulum titled "Principia" but none of them described the interaction between the ball and the disks. The following link describes the Principia pendulum in quite a bit of detail but does not address the operation of the disks. In some of the photos on the website, you can see that some of the disks are down while others are up.

http://www.jonesginzel.com/Principia.html

Cal
calr is offline   Reply With Quote
Old Mar 3, 2006, 1:20 PM   #7
Senior Member
 
Join Date: Jul 2005
Posts: 2,885
Default

Thanks for all the links..fascinating reading.
vsch1 is offline   Reply With Quote
Old Mar 5, 2006, 11:01 AM   #8
Senior Member
 
thkn777's Avatar
 
Join Date: Jun 2004
Location: Germany
Posts: 1,831
Default

I especially like #2 - it's a candidate for a "what is this?" photo. The reflections in the big ball are well captured and the small discs on the rods remind me more of a instrument (music) than a clock.

Really nice.
thkn777 is offline   Reply With Quote
 
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off



All times are GMT -5. The time now is 8:31 AM.