The start to the Balanced Forces Unit was one of the highlights last year. I loved how at the end, you could see things click as they made the connections between balanced forces and constant velocity and Newton’s First Law (“Hey we remember him!”)
I borrowed my demo and introduction of this from Kelly O’Shea (if you haven’t already, check out her Physics! Blog! – it is great!).
Although this year, the air puck I would normally use is in a cabinet that is under a waterfall that is part of a museum exhibit (don’t ask!), so I had to resort to using some stand-ins. Unfortunately the dry ice I wanted to use for the situations where the air puck would be on, didn’t move as smoothly as I had hoped. The dry ice did not really move on the tile floor except for pieces about the size of a fingernail. The counter top worked better, but several spots were too rough. We meet again tomorrow - maybe using a whiteboard under it will work better?
I started today trying to gauge where students’ were in understanding mole calculations. We had our last class just over a week ago and due to disruptions have been having difficulty getting focused on mole calculations.
Some of my students are there, some are coming along, some are showing up to class with nothing to write on or with and no chemistry binders…
After walking through the basic mole calculations, I felt that 75% of the students had enough of a background to move on. So I gave them definitions of empirical and molecular formulas, then started a few example problems.
For our next class, five day from now, they will do problems 1-3 on Worksheet 3. Let’s hope it goes well!
Today we WB the lab with my other class… the previous class spent most of the period writing their conclusions. I am trying to get them back together due to my absence last week… but I think writing conclusions together is really valuable, so perhaps they will just have to stay a day off.
yesterday’s class didn’t quite finish WB, we have a bit more to wrap up tomorrow. I especially liked this board – this group used the rolling chair and a big spring scale in the hallway. I love how this one will clearly show the mass as the slope, and the y-intercept as Ff. I am saving this one to discuss tomorrow as the wrap-up. (and to fix the backwards slope explanation…)
I am currently writing the “re-take” for my unit 4 exam, which I mostly despise. I have a few kids who have asked to do it – some are legit kids who just need more time to process, but some are those who just slacked off the first time around, and man, that angers me. I really want to move to SBG next year so the process is easier – although they will always be retaking, but it will feel more “right” to me. I can almost guarantee that most taking the re-take will do worse this time – I can see that they are not putting in the effort. But I have to let that go, I do not have control over their study habits (or lack of).
I wrote a pretty good phet lab over the weekend that I will try tomorrow. if it goes well, I will post it up!
In Honors Physics, students performed an activity to connect the graphical model for simple harmonic motion to the mathematical model and to the physical apparatus. I posted about this lab in the fall when my AP Physics B class did it. This year we are “piloting” the AP Physics 1 curriculum with Honors Physics; so, the Honors Physics classes are doing some of the same labs as my AP Physics B class. It is odd to have two different classes do the same lab at two different times in the same school year. Regardless, I love this lab as it really helps students make connections among the multiple representations for simple harmonic motion.
We whiteboarded the lab today and I thought it went really well. In retrospect, I wish I had made everyone graph F vs. a (of those that chose to keep mass constant) – instead of a vs. F… it’s so much easier to see the concepts when the slope is the mass and the y-intercept is (likely) Ff.
Now, what next? I need to come up with some net force type activity/discussion… I need to hit this conceptually again since this part was a bomb on the Unit 4 test. I guess that is today’s task!
Dr. Brett Moudling, who was a contribution to the Framework for K-12 Science Education, which is the foundation for Next Generation Science Standards, was the keynote speaker at today’s county-wide institute day. I liked how he groups the cross-cutting concepts into three related categories:
He also categorized the science and engineering practices into three categories: Gathering, Reasoning, and Communicating.
I also attended a break-out session led by Dr. Moudling. Part of the session was to make observations and build explanations for the observed phenomenon of ice cubes in isopropanol. It was a fascinating activity as so many different phenomena were observed. My group focused on density effects, index of refraction, and melting characteristics. The entire session had a long discussion about where the ice cube floats between the alcohol and water boundary. I quickly calculated the buoyancy and I’m fairly confident that 40% of the cube would be in the alcohol and 60% in the water. I don’t think I convinced the session of this as we had contradicting observations. After the session, my group added more ice and we’re pretty sure of the 40/60 split. Maybe that was confirmation bias, however. I think this would be a great activity for AP Physics 2 next year.
The final session was by Dr. Pete Ludovice from Georgia Tech. He is a chemical engineering professor and a stand-up comedian. His topic was “Making Science Fun – Humor in the Classroom.” It was a very entertaining session and a great way to end the day.
College-Prep Physics: This actually happened a few days ago, but it’s too awesome not to share.
In an attempt to differentiate acceleration practice, I gave students a few choices. They could work on practice problems, work on graph interpretations, or do an acceleration challenge. Only one group of students from all 3 of my sections decided to go with the challenge. The goal of the challenge is to determine how far up the ramp to release a free-rolling cart so that it collides with a constant speed buggy at the bottom of the ramp. Students were not allowed to attempt any collisions, but could take data in order to determine the speed of the buggy and the acceleration of the cart down the ramp.
There are several ways to determine the cart’s acceleration:
- Collect position-time data by hand and calculate acceleration using kinematics.
- Film it and use Logger Pro or Tracker video analysis
- Use a motion detector and get the slope of the velocity-time graph
This time, the group decided to try the Ubersense app to take video and use the frame-by-frame feature to extract position-time data rather than using a stopwatch. They marked off 1 meter distances and videoed the cart rolling down the ramp. No need for the whole trip to be visible within the entire video frame — we can follow along with the cart and use the frame-by-frame playback to extract position-time data from the video:
Analysis in Ubersense: The cart reached the 1 meter mark at t = 2.72 seconds
Then they input the data into Desmos and tried to find a parabola of best fit to model the cart’s position as a function of time.
Next, they found the speed of the constant velocity buggy. Then I told them how far away from the crash point (X) the buggy would start. They then calculated the time it would take the buggy to travel to the X. Then they used that time and the Desmos graph to determine the distance the cart would travel down the ramp in the same time (e.g., the starting position of the cart).
As you can see at the beginning of the post, they nailed it!