Calculating G: Simple Pendulum Experiment, problems?

[SimonChen]

I need to experimentally calculate gravity (g) with an extreme precision (+/-0,005). We thought about trying an Atwood Machine but too many problems were related to it so we've decided to switch to an Simple Pendulum (with a very long L). What are the problems related to the Simple Pendulum experiment?

Thanks!

 

[LawrenceC]

1. You should not give it a large displacement because you'll be affected by drag on the bob and string.

2. Inherent in the sqrt(l/g) equation is the assumption that sin(theta)=theta for small angles.

3. Measure the length to the CG with the bob attached and in vertical position so that any elongation (due to load) on the string will be noted. This should be done at the start in case there are temperature changes affecting the length if tests are not done all in one session.