Station 3: Period of a Pendulum

Station 3: Period of a Pendulum

Learning objectives: 2, 5

You will find a pendulum and a stopwatch (your smartphone clock works fine).

This experiment may feel familiar — you measured the period of a pendulum in Physics 1. You are doing it again now, but this time you are going to pay closer attention to what your data is actually telling you.

Part A: Thinking about this measurement

  1. You are going to time the period of this pendulum using a stopwatch. Before you start, think about what could cause your measurements to vary from one trial to the next. Make a list of at least three sources of variation. Are these sources similar to the instrumental limitations you encountered at the other stations, or are they different? How?
  2. Could you reduce this variation by using a better stopwatch? Why or why not?
  3. Based on your answers, what do you think is the best way to get a reliable estimate of the period?

Part B: Making measurements

  1. Set the pendulum swinging with a small initial displacement (less than 15°). Time 10 complete oscillations and record the total time. Calculate the period T by dividing by 10. Repeat this 8 times. Record all 8 values of T.
  2. Now set the pendulum swinging with a larger initial displacement (around 30°). Repeat the same process — 8 measurements of T from timing 10 oscillations each. Record all 8 values.

Part C: Looking at your data

  1. Look at your two sets of data without doing any calculations. Describe the spread in each set. Are the values clustered tightly or spread out?
  2. Compare the two sets. Do the periods look different between the two displacements, or do the values overlap?
  3. In Physics 1 you were asked whether these two data sets were distinguishable. What was your intuition then? What is your intuition now, looking at the raw data? You will have the tools to answer this rigorously later in the activity.
  4. The variation you are seeing in your data is not due to instrumental limitations in the stop-watch — it is something else. Based on your answer to question 1, what do you think is driving the spread? How is this type of variation fundamentally different from what you encountered at the other stations?