Little Red School House
and Elisabeth Irwin High School

A Pre-K-12 Progressive Education

Our Mission in Action

Interaction Stations in Physics

High School Science Teacher Kelly O'Shea

Earlier in the trimester was the start of some important changes in how I am viewing and structuring my intro physics class. We were just into our second day of the Balanced Forces Particle Model. On the first day, we built Newton's First Law — that unbalanced interactions mean changing velocity and balanced interactions mean constant velocity. We then spent time working in groups and making rounds through six stations (a thank you to Brian Frank for the inspiration) to observe interactions. Here is the page from the packet:

Before they started, we had already defined and focused our idea about force as an interaction between two objects. To give context to this activity, I told students that there were three pieces of evidence they could look for to notice a contact interaction: compression, stretch, and shearing. We made sure everyone knew what all three meant (almost everyone knew the first two, almost no one knew the third, but they got it from a quick sketch and recognized it when they saw it later).

So at each station, they had to identify one interaction (there were usually multiple obvious ones and they could choose any) and think through which objects were interacting and what evidence they had for that contact interaction.

After they finished the stations, I spent way less than half the time I have spent in the past on the process of giving some vocabulary to the forces (tension force, normal force, friction force, gravitational force) and in that amount of time, we also put together our first three system schemas and FBDs using examples from our first two days of the unit.

The coolest thing was how big of an effect the shift to the interaction stations seemed to have already. (Of course, time will tell more.) As we worked through the three situations, students kept using the language of compression, stretch, and shearing. I really wondered about delaying the Fn/Ft/Ff language once I saw that they felt so comfortable with what they had observed themselves, but it was already too late. It’s great to have these interchangeable terms.

Can’t wait for tomorrow when we start thinking about pushing a box on a concrete floor! (Anyone who has been through my class knows this actually is pretty exciting even though it sounds boring!)

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