Posted by RSVP on Sunday, September 30, 2007 at 5:38pm.
see below, but be certain to read this.
http://www.batesville.k12.in.us/physics/PhyNet/Mechanics/Circular%20Motion/labs/cf_and_speed.htm
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.
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!
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.