Popcorn Picker

Today in grade 9 we did a task that connects what we’ve been working on lately. We have been exploring volume calculations, and how changing a radius or changing a height will affect the volume of a cylinder.

We watched the video of popcorn picker act 1

Students were wondering about how much popcorn would fit in the tubes made by curling a letter sized piece of paper one way or the other.

They got the dimensions 8.5×11 inches, and then set off to calculate the volume of the resulting cylinders. Usually in a class someone will hypothesize that they are the same volume, but nobody in this class thought that. They had a good intuitive sense that one would be larger than the other.

There was a big misconception that rose to the surface. Some groups decided that the radius of the cylinder would be half of the circumference, instead of half of the diameter. other groups thought that the diameter would be half of the circumference. We cleared up the relationship between circumference and diameter, and circumference and radius.

I was impressed that students were trying things, and showing their work. I was very glad to see them using their strategies like multiplying decimals using the area model.

This was one of those days where it’s nice to have an air popper and some popcorn kernels! We made popcorn and filled tubes and then counted the result to verify that our answer was correct.

The taller tube had 222 popcorn pieces and the wider tube had 263 popcorn pieces.

The big takeaway of today is that a change in the radius will bring a bigger change to the volume because the radius is squared in the volume calculation. A change in height will change the volume but by a lesser amount.