EPI-simple pendulum

[jono88]

Hi has anyone done this EPI for physics before? If so could someone explain it. Thanks

[Chazef]

The simple pendulum is where you get a bob on a string, attached to a pivot point (usually where the string is tied to a bar between two retort stands) and pull it back to a certain angle then release, timing the period (well you'd be more likely to time 10 periods and then divide the results by ten because that decreases your error by a factor of 10). anyway the idea of an EPI is to determine the effect of a number of independent variables (usually 2) on an independent variable (which I assume in this case can only be the period). Possible independent variables you might choose are mass, starting angle, length of string and maybe even air resistance. The idea is that you decide to get about 6-8 measurements for each variable at regular intervals. For example you might choose mass and length, so you get a 10g ball and test that with string lengths going from 10cm-70cm at 10cm intervals. then get a heavier ball of 20g and test with each of the strings again. Then an even heavier ball and so on. If you do enough trials, you'll get a load of results (I got 192 on the EPI I'm doing, and DAYUM do repeated trials pay off, DAT accuracy). then do some number crunching (e.g. convert the time for 10 periods into the time for 1 period by dividing by ten, then average the results of your trials). Then make a family of graphs where you have pendulum period on the y-axis and e.g. mass on the x-axis with one curve for each length of string. btw I don't recommend making a 3d graph, it looks awesome but it's too complicated to analyse as easily as a family of graphs. Alright so after you get some graphs (regardless of the variables you chose), talk about the trends you see between the independent variable and the dependent variable (e.g. you might notice that as length increases, the period increases) and then bring in some theoretical stuff and compare your results to the theory. there's loads more like your standard procedure, aim, conclusion, uncertainties, but the general idea is to choose which variables to change, which one to measure, and which ones to keep fixed, then do a load of tests and talk about those tests. I'm doing a stopped pendulum, which, if you have the time, allows for deeper analysis than a simple pendulum EPI and is less boring imo. BTW major physics spoiler: the mass doesn't affect the period of the pendulum (ignoring air resistance) so if you're planning on using it as an independent variable, you're not going to have much to talk about. Good luck Oh and another tip, if you're working in pairs I recommend that both you and your partner use a stopwatch, because that effectively doubles the amount of trials and thus doubles your precision

[Alwin]

I'd just like to add, my mate also did a simple pendulum but since he goes to the crazy school (JMSS) they also analysed motion using calculus (outside of the course). The main point that he inspected was at what angle the harmonic motion 'breaks down', as well as the others that Chazef mentioned.

If you want some extra theory of simple harmonic motion (SHM) without having to resort to wikipedia, I can send you the notes I gave my mate to help him with his pendulums. It's a mathematical breakdown of the motion as well as angle approximations of when the simple pendulum SHM stops, etc (ie some uni stuff in there) but explained in laymans terms

Good luck with your EPI