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Posted by 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 - , 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 - , 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 - , 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 - , 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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