Check Out This Huge Earthworm!

You can see what the worm looks like compared to my hand and my foot. I am a grown-up, but I am a very small grown up. How long do you think the worm is? More than 1 inch? More than 6 inches? More than a foot? Why do you think that?

Depending on how old they are, children are likely to have had different experiences with measurement units like inches and feet. Very young children probably won't have a good sense of how long an inch is, while older children might have used rulers to measure in inches, feet, yards, centimeters, and meters. They will be able to think about their experiences measuring objects to estimate the lengths of other things (like this worm) that they have not yet measured.

What do you notice about this ruler?
A ruler is a tool we use to measure how long something is. This ruler has markings and numbers we can use to measure how many inches long something is.

Look at the different ways we lined the ruler up with the worm to measure it. How many inches long do you think worm is? Why do you think that?
If you line the worm up with the end of the ruler, you can use the number at the other end of the worm to see how many inches long it is. If you don't, you need to think more carefully about how many inches (an inch is the distance between two numbers on the ruler) are equal to the length of the worm.

In the first picture, the worm starts at 0 inches and extends to 7 inches. It appears to be 7 inches long. In the second picture, the worm more than spans the distance between 4 and 11 inches marked on the ruler: it appears to be a little more than 7 inches long (the 7 inches between 4 and 11, plus a little more on either end).

When students are new to measuring, the idea that something (like this worm) needs to be laid out straight (as it is in the second picture) is a big idea. So is the idea that that each labeled interval on the ruler represents an entire inch. Students who have little experience with measuring will look at the second picture of the worm and report that the length is about 11 inches. It takes time and experience for children to understand that the numbers represent the number of whole inches from the 0 end of the ruler and that it's the spans between those number that represent an acual inch.

What fraction of a whole foot is the worm?
The worm measures about 7 inches. That's 7/12 foot (because a whole foot is 12 inches). The worm is a little more than half a foot long.

Check out this picture ... the worm looks longer! In the pictures above the worm appears to be about 7 inches long. How long does it appear to be here?
The worm, which is stretched out nice and straight appears to be about 10 inches long. That's 3 more inches than it appears to be above.

As we watched the worm, we noticed that it moves by stretching itself out and then contracting. If it wasn't on the move, it was just kind of relaxed, neither stretched out nor contracted. Depending on where the worm was in its stretching and contracting, it measured longer or shorter. If someone asked you, "Whoah! How long is that worm?!" what do you think a reasonable answer would be?
There's no right answer. You could report the range "between 7 and 10 inches long" or the midpoint between the maximum and minimum "about 8 and a half inches long."
You could report the length relative to some benchmarks: "It's more than half a foot, but less than a whole foot" or "Between half a foot and a foot."

We were really excited about this worm because it was way longer than most worms we've ever seen. (So exciting!) But then we wondered, "Is this as big worms get? Could there be worms even longer than this one?"

You bet! Check out this video of the inimitable Sir David Attenborough gently and carefully introducing us to the largest earthworms on the planet.

How many times longer is David's worm than ours? How many of our worms would we have to line up to equal the length of David's giant earthworm?

Can we find more worms to measure? If we collected data about worm length, how could we ensure that our measurements were good for comparing the worms? Would we measure them in a relaxed state, all stretched out, or all scrunched up? How many times would we measure each worm? ...