How do I handle uncertainties in pendulum length for my physics lab?

[JoshuaA]

I’m really stuck on how to approach my physics lab report on pendulum motion. I’ve plotted the period against the length, but I’m not sure how to properly discuss the systematic uncertainties in my measurement of the string length.

[ZoeyIM]

I did the same, measured from the pivot to the bob’s center with a ruler. The pivot mark isn’t fixed and the stand tilts, so the measured L shifts. The string also sags under gravity, so the effective length is a bit longer than the reading. Parallax from eye level reading ruins repeatability.

[BenjaminJR]

I tried a vertical reference line on the stand and used a tape to read to the bob center, taking several trials from different sides. The big systematic errors were where you define the pivot and whether you measure to the bob’s center or the end of the string, plus the path of the string when it’s not taut.

[GaryM]

I wondered if the bigger issue is that the angle wasn't small. If the amplitude was a few degrees, the period shifts a bit, which can look like a length error. So distinguishing L error from amplitude effects is tricky.

[Dennis.B]

I did one thing different: marked both ends of the string and recomputed length from those marks, still saw that small changes in distance changed T. Do you think the problem is really length or something else?