Pendulum Lab

This week I’ve had one and a half Algebra II classes to “kill” because I’m ahead of the other teacher and we need to sync up again. Since we’re working on parabolas, I thought we could do something fun.

A while ago, I watched this video:

And I decided, perfect! I’m going do the pendulum thing in class. I got some string and washers, and put masking tape on the string every 6 inches. And I had student calculate the period of the pendulum when the length of the string was 6 inches, 12 inches, 18 inches, … , 60 inches.

To minimize the error generated by a student not exactly stopping the stopwatch when pendulum swung back and forth, I had students have the pendulum swing three times. That way any reaction time error of the person operating the stopwatch gets reduced by a third! And I had students do 3 trials for each length of string, to further minimize error.

It took all 50 minutes for students to collect all their data, plot it on a graph, and enter the data in their calculators.

Tomorrow we get to have fun. To warm up, we’re going to talk about sources of error. Then each group will get to share their graphs and talk about their findings. Then we’re going to perform a quadratic regression on our calculators, talk about if we have a good or bad model and ways to decide, and then use our model to make some predictions. (If we know the period, can we find the length of the pendulum, and vice versa.) Then, I’m going to conclude by showing students the theoretical formula for the period of a pendulum (T=2\pi\sqrt{\frac{L}{g}}) and we’re going to see if their collected data matches up with the theoretical predictions.

The best part about this is that all the groups data seems in line with each other, and in fact, they are all really close to the theoretical predictions. I can’t wait to see if there are oohs and aahs about how accurate these data points they got are to the theoretical predictions.

I’m excited for tomorrow!

UPDATE: my data collection sheet (PDF), my lab debrief sheet (PDF).



  1. all the groups data seems in line with each other, and in fact, they are all really close to the theoretical predictions.

    You really should have this tshirt to wear for this lesson.

  2. That’s a creepy video.. I did this when I was in school and it actually…
    wasn’t fun at all. (by the way, I thought in the experiment your suppose to shorten the sting.. not lengthen it, oh well it can be done either way it’s just showing you about graphs and recording data ect. ) *shrug*

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