Posted by RSVP on Sunday, September 30, 2007 at 5:38pm.
I have 2 questions...one can someone please read my question posted around noon today called Lab for physics? Thanks..and secondly, I have to derive some equation. I am supposed to show a=gtantheta and find this from m (mass) L (length). The question also mentions the verical axis..nothing really helpful! Any ideas on how to do this derivation?

Physics  bobpursley, Sunday, September 30, 2007 at 5:47pm
see below, but be certain to read this.
http://www.batesville.k12.in.us/physics/PhyNet/Mechanics/Circular%20Motion/labs/cf_and_speed.htm 
Physics  bobpursley, Sunday, September 30, 2007 at 5:51pm
Consider the bob spinning: centripetal force is outward, and gravity is downward.
Then the string makes the angle theta with
tan theta= mg/m*a =g/a where a is centripetal acceleration (v^2/r)
If you measure the other angle, then tan theta is a/g, so it depends on which angle you are measuring. Normally, we measure the first, string angle from horizontal. 
Physics  RSVP, Sunday, September 30, 2007 at 7:09pm
So I understand the lab thing now completely! Thanks so much..and I sort of understand what you are doing for this derivation, but can you give some more of an explanation for where you are getting the equations from? Thanks a million!

Physics  bobpursley, Sunday, September 30, 2007 at 7:23pm
centripetalforce= m*v^2/r where m is the mass of the spinning mass
gravity force holding it= mg where m is the washer weights
If r is constant, the two forces are equal, set them equal.
sometimes centripetal force is written as mw^2 r where w is angular velocity, but it is easily shown as above.
You measured period to go around, so
v=2PI r/Period
The rest is math, and critiquing error.