I decided to start this year with the Balanced Forces Unit after discussions with Frank Noschese and Kelly O’Shea. Today I introduced the Slinky Drop problem as a preview of a phenomenon we’d be able to predict after this unit. After we discussed it a bit, I showed them the Veritasium Science Trailer which includes a slow motion clip of the slinky falling during the last few seconds.

We then followed Kelly’s Common Types of Forces sequence to talk about different types of forces. Gravity was pretty straightforward, but the students were not entirely convinced about the existence of normal force. Without the Pasco Matter Model or students’ familiarity with the idea that atoms can be thought of in that way, the development was more difficult.

Below you’ll see a picture of a setup to demonstrate normal force from Preconceptions in Mechanics that I used in class today. It seems to me that the explanations for the existence of the normal force hinge on the relationship between deformation and a force. Because the books bend the ruler, the ruler must be exerting a force upward on the books. The reason that deformation is indicative of the existence of a force makes sense to me, but I don’t know how to effectively help my students understand it. We did pass around springs and foam for students to feel that when they deformed those objects they experienced a force, but I don’t think they were convinced about the general case.

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In Algebra I started the day with Estimation 180 and followed that with the Ages of Three Children Puzzle. I really like that puzzle, because it seems like there isn’t enough information to solve the problem, but once you start working on it and listing the factors of 72, the solution starts to become clear. I wanted to emphasize to them that it can be effective to start working on a problem even if you’re not sure how you’ll get to the answer. Once they started working I regretted not using the version of the problem where the product of the children’s age is 36 rather than 72 which would have made the factoring a bit easier and quicker.

Thanks for reading! I’ll be back on Monday after our second day of school…