# Day 3: What does a negative acceleration mean?

We didn’t answer that question today, but we asked it a lot. Almost everyone in the class has really wondered that on their own by now. One student has proposed that it has to do with the direction of the forces, but that didn’t get much traction (yet). We will come back to that question and idea soon enough.

We worked through their findings from that first day activity (today was day 2 of Mechanics), and even though they started out in a goofy sort of mood, they got pretty serious in trying to nail down all of the features of the velocity graph and what they told us. (What does it mean if the velocity graph is above the time axis? Below? Getting closer to it? Farther? Etc.)

Part of the board above shows different ways for a velocity graph to have a (constant) positive slope and different ways for a velocity graph to show a positive velocity. It was something one student decided to draw to try and help people piece things together.

They dove into some tough TIPERs questions in the second half of class, and we will whiteboard them tomorrow.

And here are some bonus photos from other classes today (I had all of the classes). 9th graders burning steel wool (and snapchatting it, because of course), drawing particle diagrams for various experiments, and having board meetings. 9th graders wearing lab coats to make whiteboards (the coats are “comfy!”). Relativity kids making a “river” and a “motorboat” out of buggies and butcher paper.

A conversation with Donghong and Alan after school helped me realize a point or two that I missed in the whiteboard discussion so far (which we can pick up in our next class on Friday) and reflect on some things that have gone well in these first two days of Chemistry 9. I love how quickly they are ready to use evidence to support their ideas, to reference earlier experiments as part of that evidence, and to use diagrams as sensemaking tools. We’re already having real scientific discourse, even if we are just beginning to learn how to do that together.

Great student quote of the day: “Oh! That’s why they call this relativity.”