One of our first tasks has been to collect some data on an object known as a “simple pendulum.” There’s no perfect simple pendulum, but instead this term is used to describe something that swings back and forth with all of its mass stuck to the end that’s swinging. A yo-yo swinging back and forth is a good example, or maybe a tetherball at the end of its cord; but lots of things are really close to a perfect simple pendulum. In fact, I was counting on the fact that you could find something that would work, likely right there in front of you.

Here are the instructions I gave for setting this up:

Then, you each collected data from your own objects: keys at the end of a lanyard, the adapter at the end of an electrical cord, a weight at tied to the end of a string, etc. These all work — though you might wonder if it’s okay to all be using different things if we’re going to share the data with one another. That’s a good question, and we’ll get to this.

After everyone reported data for the length of their pendulum and the time it took to swing 10 times, I took all of that and made a graph. Here’s an example:

I love this graph for a few reasons. First and foremost, you each collected ONE piece of data, and that single piece of information didn’t tell you very much. But now we have it in the context of all the other data. You can see how yours compared to others. More important, you can see if there are any patterns in these data. To me, it looks like there are. I tried to sketch some of what I’m seeing right on the graph:

MOST of the data show that the shorter strings take the least amount of time to swing, and the longest strings take the greatest amount of time. In addition, it looks like those times change most drastically when we change the shortest strings, and they change less for the longer strings. This makes a kind of curve that seems to be getting flatter and flatter as you go from left to right (shorter to longer strings). There’s a pattern here, and your data likely fits right into it. But we needed lots of these experiments in order to see the bigger picture. In fact, now we can even imagine that this curve could be described mathematically. Nature actually abides by this mathematical relationship — or maybe it even invents the mathematical relationship for which we needed to invent the mathematics!

For now, I’ll leave you with a few questions:

• Seeing that there’s a pattern here, what do you think a shorter pendulum would do? A longer pendulum? In other words, does this graph/pattern tell us about other pendulums we didn’t collect data for?
• I never told you to use a specific kind of object, so people probably used objects that had different masses (or weights). They probably also had bigger and smaller swings. Since we didn’t account for those variations, what might that mean?
• Not everything fits the pattern perfectly, and there are definitely a few outliers. Why? What do you think happened? What does this tell us about collecting data, conducting experiments, and creating investigations? Or, maybe more broadly, what does this tell us about science? Can we trust it?