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September 18, 2014

September 18, 2014

Posted by **RSVP** on Sunday, September 30, 2007 at 5:38pm.

- Physics -
**bobpursley**, Sunday, September 30, 2007 at 5:47pmsee 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 5:51pmConsider 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 7:09pmSo 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 -
- Physics -
**bobpursley**, Sunday, September 30, 2007 at 7:23pmcentripetalforce= 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.

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