Misc. Can anyone suggest a suitable material for a Foucault pendulum platform?

[Charles Link]

1. The intent of the assignment is surely not "ask some people on the internet to do the research for you". This makes me crabby.
2. Spamming the forum with multiple requests for us to do #1 also makes me crabby.
3. Some of your questions can be answered by building a regular pendulum. I would recommend that as a starting point.

I think it could be very useful for 3 or 4 people to try to make this a group effort. The project is difficult enough, that there are many who have said that it can't be done.
And for a good book on this topic, see https://www.amazon.com/dp/0743464796/?tag=pfamazon01- years 20 I read this book about 10 years ago. It is very good reading, and it even has the derivation of Foucault's equation for the period as a function of latitude in the appendix. If I remember correctly, it is $T=\frac{T_o}{\sin{\theta}}$, where $T_o=24$ hours. I believe in the book, it said Foucault simply had an M.S. degree, and other famous mathematicians and physicists of that time did not have an answer for the period of his pendulum.

 

[Charles Link]

[Moderator note: A second thread on this same topic was started yesterday. Posts in that thread were merged into this one.]

The first one on the do-it-yourself Foucault pendulum began May 15, 2018. It seems to be a very good idea to merge the two threads. It looks like the previous participants are very happy to share their experiences.

 

[JBA]

Depending on the size of the surface you need you might consider one of the below sapphire discs. in smaller diameters they are very inexpensive .ie. the example : .250 in diameter shown is $7.60 for 1 pc. Both ruby and sapphire have a hardness of 90 on the mohs scale.

https://www.swissjewel.com/product/sapphire-windows/w6-30/

 

[lesaid]

Just discovered the recent posts here! I've been away from this project for some months (studying other things) and will be returning to continue my efforts some time in June or July. In the meantime, I am happy to exchange ideas and experiences with others engaged in the same kind of thing.

One of the recent posts suggested building a regular pendulum as a starting point. I started by using household string tied to a hook in the ceiling to suspend a bag full of nuts, bolts and other metallic scraps, including a small reel of solder if I remember right. Anything I could find to make a decent weight! Of course it was useless as a Foucault pendulum but it was a good starting point, and taught me a lot about how free pendulums swing (and how string 'unwinds' under tension!). Then proceeded to improve the pendulum, one component at a time until I arrived at the one described earlier in this thread.

Next step will be to rebuild the suspension platform to be much more rigid and finely adjustable for level, and explore using an off-the-shelf ruby bearing as the pivot support platform (if it is available at a sensible cost). Along with trying to develop a better mathematical model of how the pivot should behave on a sloping platform, and on a ruby bearing with a concave supporting surface. I'm a bit nervous as to how much force I can apply to a hard ruby ball 1 mm in diameter resting on an equally hard ruby surface without the ball cracking, but not sure how to calculate it so I'll have to try it and see!