Determine g from a pendulum by linearizing the data
Three steps, the way the exam actually works: work through the lab, write down your own measurements, then answer a 6-point free response. What you recorded goes to the grader with your writing, so a conclusion that does not follow from your own numbers will cost you the point — exactly as it would with a real reader.
Predict before you look
- T = 2π√(L/g). Square both sides: what is T² proportional to, and what quantity plays the role of the slope?
- List every quantity you believe the period of a pendulum depends on, before you take any data. Step 5 checks one of them directly.
Nothing to submit here — these are to think through, so the prediction below is an informed one rather than a guess.
Commit to an answer now. It is not graded and being wrong costs nothing — the point is to have something specific to reconcile against once you have the data.
Answer every prediction to unlock the lab. A sentence is enough.
Run the investigation
Predictions first
The procedure and the simulation unlock once you have committed above. Observing before predicting is how a wrong intuition survives a lab intact.
Record what you measured
These are your numbers, not ours. The grader sees them, so your conclusions have to follow from what you actually recorded.
| Period at L = 0.50 m | s |
|---|---|
| Period at L = 1.00 m | s |
| Period at L = 1.50 m | s |
| Period at L = 2.50 m | s |
| Period at L = 1.00 m after changing the bob mass | s |
Answer the free response
You are asked to determine the local gravitational field strength from pendulum measurements. (a) This simulation reports the period exactly, but in a real laboratory you would start a stopwatch and time ten oscillations rather than one. Explain why, and identify which type of experimental error that technique reduces. (b) A classmate plots period against length and gets a curve. Explain what you should plot instead to obtain a straight line, and derive the expression for the slope of that line. (c) Using your data, calculate a value for g. Show your work and give appropriate units. (d) Using your mass measurement, state whether the period depends on the mass of the bob and justify your answer with both your data and the governing equation.
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