# Physics

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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 -

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 -

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 -

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 -

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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