# Day 42: Mass & Comet Orbits

AP Physics: Mass

Students finished the lab practical we started on Thursday where they used a modified Atwood’s machine to find an unknown mass. Today, once they had an answer, we checked their result using a spring scale. One of my goals this year is to work on hearing from every student, so I tried posting three questions about the lab (one for each group member). Then, before groups could check their result, I would roll dice to decide which group member had to answer each question. Since there are three students in each group, I was able to hear from every student. Groups did a really nice job of making sure all three group members could answer all three questions, which is exactly what I hoped would happen.

Earth Science: Comet Orbits

Students finished up yesterday’s lab contrasting Mars’ orbit with Halley’s Comet’s orbit. A lot of groups were surprised when they realized that the patterns from Kepler’s Laws worked equally well for both orbits, especially when they used mass as a proxy to compare the areas of two sections that represent equal times. Next time, I might see if I can get my hands on some card stock or other heavier paper to make it a little more convincing that the small differences are negligible. I also will probably re-work my Kepler’s Law introduction to include Halley’s Comet right off the bat, rather than waiting until we introduce comets.

# Day 40: Mass & Craters

AP Physics: Mass

Students worked on a lab practical to find the mass of an unknown object using a modified Atwood’s machine. My plan is to use spring scales to verify the mass the determined, then use this to introduce the difference between inertial mass and gravitational mass, but time got tight and most groups need a little longer to finish their calculations.

Earth Science: Craters

During yesterday’s lab, it quickly became clear that my students did not have much sense of how craters are formed. Today, I got out some trays of sand and an assortment of marbles and we explored how mass and impact speed affect the crater size. I was really excited when the groups who finished early started asking new questions, like how the depth of the sand or angle of impact changes the crater, and coming up with experiments to answer those questions. This is why I love freshmen! We also dropped a shot put into a bigger tray of sand and got some slow-motion video just because its cool.

# Day 108: Balances & Isotopes

Physics: What does a balance measure?

A couple of students turned in their work from yesterday to my sub, and I saw they pretty consistently interpreted the balance in the video as measuring mass rather than force. To help clear that up, I took a balance on the school elevator and recorded some video. We started by drawing some free-body diagrams, then connected those to changes in the reading on the balance to get at what the balance is really measuring. From there, students whiteboarded and shared their answers to yesterday’s activity.

Chemistry: Isotopic Pennies

To introduce the idea of isotopes, students got sealed jars with 10 pennies and had to determine how many of their pennies were made before 1982 without opening the jar.

# Day 17: Weight & Acceleration Practical

Physical Science: Weight

Today began with some talk about the engineering design process developed by EngrTEAMS. In particular, we placed ourselves in the “Learn” phase since students agreed they need some new science to understand crashes. I introduced forces as a tool for understanding crashes, and we dove in to a lab where students used spring scales to measure the weight of several hanging masses, then graphed the results. Tomorrow, we’ll get to the idea that the slope is the strength of gravity.

Since the lab is fairly straightforward, I had the chance to do one-on-one conferences with a few students who currently have low grades to make an action plan. I’m taking an “SBG-ish” approach in the course, which means I enter unit tests in the gradebook, rather than standards, but the tests are nearly all of the grade and I allow retakes to replace the initial score. I really liked that this freed me to talk with students about missing skills and understandings, rather than a long list of missing assignments. The students also seemed much more positive about these conferences than in the past.

Physics: Acceleration Practical

For most of the hour, students started working on a lab practical where they will roll a marble down a ramp so that it lands in a tumble buggy as it drives past. As a class, we collected the data students need to get the speed of the buggy and the acceleration of the marble, then students drew a random starting position for either the marble or buggy. I introduced the practical very clumsily in my first class, so I’ll need to do some clean up and clarification when we get back to the practical on Friday.

The first part of the lesson was finishing yesterday’s whiteboard presentations and produced one of my favorite moments of the day. When preparing their whiteboard yesterday, one group made the very common mistake of using v = d/t to find the final velocity of an accelerating object. In their quick conversation, they realized their answer didn’t make sense with the other values and were able to correct it. That group was brave enough to share that mistake, as well as how they caught it, when they presented the problem.