# Measuring the Velocity of a Marble or How to have a Rockin’ Math Lesson

As I was finishing up on my computer one morning last week, I was reflecting on what type of family math lesson we’d have for the day when I heard the kids in our playroom having a good time building and testing a marble roller coaster. The roller coaster rocks because you can watch the marble the whole time. It rides on top of a track. How is that not fun?

That’s when it came to me…so I shouted downstairs…do you want to find out how fast that marble is going?

The reply came quickly and loudly, “YEAH!!!”

So, we gathered at the school table and did some brainstorming. The first thing I asked them is what they thought we might need in order to find out the speed. We quickly determined we did not have any equipment that could just measure speed. E11 remembered from our Explorers unit last spring (He read Carry On Mr. Bowditch) that we just needed to measure the time it took the marble to go a particular distance. Woohoo!

So we talked about how we might measure the distance of the track. They had a lot of really good ideas. R9 suggested that the distance between the rails of the track were the same and we could measure one and then count how many there are and multiply to get the length of the track. Then they thought instead of the individual rectangles, they could measure track spans and add them up. Of course allowances and special measurements would need to be addressed at the curved track pieces.

They came up with using a sewing tape measure which could bend and finally using yarn to mimic the track and then measuring the yarn length which is ultimately what they chose. Very interesting to watch this process. We did discuss later on which would be the most efficient and perhaps the most accurate method, but I let them explore because that’s what it’s all about.

The start of the track- it began high on the toy shelf and made a drop to a loop-d-loop.

This track ended in the “kitchen oven” where the marbles collected on cookie trays.
There was a problem with the track at the turn. Sometimes it’s hard to get the marble to negotiate the turn in the track. In the end, we had to have two ways to write down our time- one for runs of the full track and one for runs only to the curve.
I had the kids take turns writing on the chalkboard the things we’d be measuring or finding out- in the case of the speed of the marble.

In the end they decided to go with using yarn to determine the length of the track.

In the next post, I will share the results and how the kids determined the speed of the marble. We had some good discussions about the realities of being a good scientist.

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