Experimental design and analysis (LAB)

Measuring g with a pendulum

Unit 7
10 points
About 27 minutes

You can use a calculator on this question, just like on exam day.

A two-part lab question. First you design an experiment to answer a question: what you change, what you measure, the equipment and how you would analyze the data. Then you get a data table from a similar experiment, choose what to graph (often so the points fall on a straight line), plot it and use the slope, the intercept or the graph's shape to answer a question. On the exam: Question 3 of 4. Section II has 4 questions in 95 minutes (50% of the exam score), one of each type in this order; calculator allowed. The CED suggests 25–30 minutes.

The question and its sources

Students want to determine the acceleration due to gravity, g, at their school using a simple pendulum.

Part A: Available equipment

A long piece of string, a set of small metal bobs of different masses, a stand and clamp to hang the pendulum, a meterstick, a protractor, and a stopwatch.

Source: Hypothetical lab setup

Part B: Table 1. Another group's data (small amplitude, same bob)

Pendulum length L (m)	Time for 10 complete oscillations (s)
0.20	9.0
0.40	12.6
0.60	15.6
0.80	17.9
1.00	20.1

Source: Hypothetical data

Suggested time: 27 minutes

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Part (A(i))

3 points

Describe an experimental procedure you could use, with only the equipment listed, to collect data that would allow you to determine g. Include what you would measure, what you would change, and any steps you would take to reduce experimental uncertainty.

Your answer to part (A(i))

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Part (A(ii))

2 points

Describe how you would use your data to determine g. Include what you would graph and how the graph would give you g.

Your answer to part (A(ii))

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Part (B(i))

1 point

Using the data in Table 1, indicate which quantities you would graph to produce a straight line that could be used to determine g. Calculate the values you would plot.

Your answer to part (B(i))

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Part (B(ii))

2 points

Plot the quantities you chose and draw a best-fit line. You can't draw here, so describe the graph you would draw: what goes on each axis (with units), the scale, the points you would plot (list their values), and the best-fit line.

Your answer to part (B(ii))

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Part (B(iii))

2 points

Use your best-fit line to calculate an experimental value for g.

Your answer to part (B(iii))

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