Teach lesson
Pendulum: how length affects the period
Lower-secondary (4 ESO) activity that uses the Pendulum remote lab to measure real periods and decide how the period changes when the pendulum is made shorter or longer.
Learning Outcomes
Tell apart period, oscillation, amplitude, length, and the variables of an investigation.
Use the Pendulum remote lab to measure the period of a standard pendulum and a short pendulum at the same initial angle.
Calculate mean periods and plot a graph of period against pendulum length.
Write a conclusion with claim, evidence, reasoning, and uncertainty.
Student activity preview
Activity Content
Preview only. In a class session, students can fill in responses and submit their work to the teacher.
Before you open the lab
10 min
In this activity you will investigate one specific question:
What happens to the period of a pendulum when its effective length changes?
You will use data from the remote lab, not a memorised answer. In a real experiment the measurements never come out perfectly: two groups can get slightly different periods if they pick different points on the graph or count a different number of oscillations. What matters is that your method is clear, that you keep the other variables under control, and that your conclusion uses your own data.
Vocabulary you need before you measure:
- Oscillation: one complete back-and-forth movement. For example, from one side, across to the other side, and back to the starting side.
- Period, T: the time for one complete oscillation. It is measured in seconds (s).
- Amplitude: how far the pendulum starts from the vertical. In this lab you control it with the initial angle.
- Effective length: the distance that makes the pendulum behave as if it were longer or shorter. In this activity you compare it using the standard and short configurations.
- Independent variable: what you change on purpose. Here it is the effective length: standard versus short.
- Dependent variable: what you measure to see the effect. Here it is the period T.
- Control variables: what you keep the same so the comparison is fair. Here they are the initial angle, the measuring method, and the number of oscillations used in each calculation.
Configurations you need for this investigation
For this activity use only the standard and short configurations. The soda-can images appear because they exist in the lab, but you do not need them to answer the question about length.
Identify the variables of the experiment. Answer with three short sentences or a list: one sentence for the independent variable, one for the dependent variable, and one for at least two control variables.
Before you measure, write your prediction. Answer in 2 or 3 sentences: say whether you expect the short pendulum to have a smaller, equal, or larger period than the standard one, and explain your reason using the idea of length.
Measure in the remote lab
15 min
You will measure the period with the initial angle fixed at 15 degrees. That angle is inside the lab's visible range and lets you compare lengths without mixing in the effect of amplitude.
How to measure a period on the graph
For each configuration, take three period measurements. For each measurement:
1. Open an observation with the configuration shown.
2. Use the initial angle of 15 degrees.
3. Look at the graph of angle against time.
4. Pick an easy-to-recognise point, such as a peak, a trough, or a crossing of the centre line always in the same direction.
5. Count at least 3 complete oscillations from that point to another equivalent point.
6. Write down the start time and the end time in seconds.
7. Calculate interval = end time - start time.
8. Calculate period = interval / number of oscillations.
You do not need to download CSV, XLSX, or PNG to complete the activity. If the lab lets you download data and you want to use it, you can, but your main evidence will be your table and your explanation of the method.
Open the Pendulum lab
Open the Pendulum lab from Teach.
Select the standard configuration.
Set the initial angle to 15 degrees.
Start the observation, use the graph or the chronometer, and complete three measurements.
Repeat the process with the short configuration, keeping the angle at 15 degrees.
If your session only allows demo mode, record that you could only open the standard pendulum at 15 degrees, and use the data your teacher provides for the short configuration. Do not write that you measured a row you could not observe.
Choose one option. Which comparison is fairer for investigating the effect of length?
Record and calculate data
14 min
First complete the measurements table. Each row is one period measurement: three measurements for the standard pendulum and three for the short pendulum. Copy the configuration and trial already shown. In initial angle, write 15. In complete oscillations, write how many complete oscillations you counted, for example 3, 4, or 5. In start time and end time, copy the times you read from the graph or chronometer. Calculate interval = end time - start time and period = interval / number of oscillations. In evidence used, write something like graph peaks, zero crossings, video chronometer, or teacher data because of access limit.
Period measurements at 15 degrees
Complete six rows: three trials of the standard pendulum and three of the short pendulum. Use seconds. The interval is end time minus start time. The period is the interval divided by the number of complete oscillations counted.
| Configuration / length | Trial | Initial angle degrees | Complete oscillations | Start time s | End time s | Calculated interval s | Calculated period s | Evidence used |
|---|---|---|---|---|---|---|---|---|
Now summarise your results by length. The table has two rows: one for standard and one for short. In periods used, copy the three periods from the table above. In mean period, calculate the mean of those three periods. In range, subtract the smallest period from the largest period of that same configuration; use it as a simple sign of uncertainty. In graph label, write the label you will use on the horizontal axis: short or standard.
Summary for the graph
Complete two rows, one for each length. Calculate the mean of the three periods and the spread (range). Do not look for an exact match with a textbook value: use your own data and keep a sensible number of figures.
| Length compared | Periods used s | Mean period s | Range between measurements s | Point for the graph |
|---|---|---|---|---|
Enter a numeric period value in seconds and explain the calculation in 2 or 3 lines. Use one specific row from your first table: state the interval, the number of oscillations, and the division you did.
Compare your three measurements of the same configuration. Answer in 2 or 3 sentences: say whether they came out very similar or spread out, quote the range of one configuration, and explain one possible cause of that difference.
Plot and interpret the relationship
9 min
You will build a simple graph of mean period against compared length. On the horizontal axis put two points: short and standard. On the vertical axis put the mean period in seconds. If you use a spreadsheet, create two columns: compared length and mean period (s). If you do it on paper, plot the two points and draw a smooth line only to help see the trend; do not use it as an exact proof.
Period-length graph
Submit evidence of your graph: an image or screenshot, a link to a spreadsheet, or a graph checked by your teacher. The graph must show at least the two points short and standard, with the mean period in seconds. If you cannot upload a file, write a description complete enough for the teacher to know which points you plotted.
Interpret your graph. Answer in 3 or 4 sentences: say which point has the larger period, which point has the smaller period, roughly how much the mean period changes between the two lengths, and whether that change is larger than your uncertainty range.
Scientific conclusion
7 min
Choose one option. Which statement is the most scientific for this activity?
Write your conclusion using the structure claim, evidence, reasoning, and limitation. Write a paragraph of 6 to 8 lines:
- Claim: what effect making the pendulum shorter had.
- Evidence: quote the mean periods of the short and the standard, and the approximate difference.
- Reasoning: connect the pattern to effective length and the time of one oscillation.
- Limitation: mention the uncertainty, the limited number of lengths, or an access limitation in the lab.