The Marshmallow Challenge… Starting Physics with Equilibrium

Back in July, Mylène DiPenta shared on Twitter their twist on the Marshmallow Challenge. I had never heard of the challenge, but like many other physics teachers I was excited to try this approach, especially since it’s an excellent way to begin the conversation about Standards-Based Grading, or in my case, a portfolio-based approach to grades.*

*It’s not quite gradeless, but I’m headed that way!

My first day of physics went almost exactly as Mylène describes. After I said, “How fast can you get your marshmallow off the table?” one group immediately placed the marshmallow on the one-noodle thick layer of spaghetti and, after seeing my smile in response, another group nervously copied them after half a minute had gone by. A couple of groups went straight to trying to support the marshmallow at the top of a triangular pyramid, which worked well with a few tries. Finally, one group balanced their marshmallow on the toy airplane hanging from the ceiling above their lab table.

I congratulated them on their structures, clarified the rules a little for the group grinning sheepishly next to their airplane, then tasked my students with building as many and as tall structures as they could with the time remaining. As soon as a team finished a new structure, they wrote the time remaining and height on their whiteboard. Between the seven groups, the class constructed 24 stable structures in the time allotted.

What interested me is that nearly all the groups had similar first, second, third, and fourth structures:

It was only halfway through the building time that I realized how this activity perfectly introduces my curriculum, since I begin my AP Physics 1 class with equilibrium.* In simplest terms, this is a static equilibrium problem. In the first prototype, three sticks of spaghetti support the marshmallow such that (up forces) = (down forces), (left forces) = (right forces), and, because this is a three-dimensional problem, (front forces) = (back forces). If the students understood this, they would realize that in their following prototypes, they were effectively trying to counter the gravitational force on the marshmallow with a single stick of spaghetti, which works only when the base is sufficiently wide to account for any leaning.

*Inspired Greg Jacob’s posts on doing physics on the first day of school and starting with equilibrium and skipping vector math with a quantitative demo on day 2.

While there’s an element of torque that I won’t introduce until later in the year, there are a few facts at play that my students will learn in the next two days of class:

• The only objects exerting force on the marshmallow are those touching the marshmallow.*
• An object at equilibrium has (up forces) = (down forces), (left forces) = (right forces).
• Angled forces can be broken into vertical/horizontal components.

*With the exception of the earth, which is responsible for the only long-range force we discuss in these early days.

I promised my class that, as physics students, they are entering the ranks of those with specialized skills described by Tom Wujec. I think that after a week of class, we could easily repeat the marshmallow challenge and show that promise to be true. I’ll be back and update if we get that chance!

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Have you used the Marshmallow Challenge? How do you connect it to your curriculum? Is there something I haven’t thought of yet? Let me know in the comments!