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 -
**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.

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