Physics 11 – Students conducted a lab on Hooke’s Law today. They were prompted to model the relationship between an external force and how it affects a spring it is acting on. Data collection went pretty well and I strongly suggested that students use Excel to produce their graphs. Several groups opted to hand graph their data, which was very surprising to me. However, after pointing out a few things that they could do to improve their graphs, most of these groups eventually realized that re-doing it in Excel would be a lot of faster and probably more accurate.
Physics 11 – Oops, no photo today. I was pretty busy helping kids collect data for constant acceleration. Photos would be just like the ones from this post.
Data collection went pretty well and most students were able to finish plotting their position-time graphs.
Physics 11 – Today we continued with our investigation into mirrors. Students found the focal length of a mirror by projecting an image from a distant object. Next they were asked to find the image distance for a given object distance, using three different methods: direct measurement, calculation using the focal length, and doing a scaled ray diagram.
As I noted from last day in physics, I hoped that students could use a cooperative learning environment to successfully solve mirror problems. It turned out that the substitute felt that kids should work quietly and independently. Uh huh.
Science 8 – Following from last day, a few kids designed an experiment where they wondered what would happen to the pouring rate if the temperature was changed. That’s fantastic, because there is another lab in the textbook that covers this.
Today’s lab focus is data collection and graphing. They’ve already worked on experimental design and the procedure for this test isn’t very obvious. The graphing is a bit difficult though, because after the temperature of corn syrup reaches 55C, the data gets unreliable. They are measuring the time it takes for a steel BB to drop through 200 mL of heated corn syrup, and after 55 C the viscosity is so low that the time is less than 1 s. This makes timing very unreliable and inaccurate.
I looked over the Smarter Science sheets that the kids made and it was pretty good. The most difficult part of this process seems to be picking the dependent variable. What can the observe or measure that will determine if there is an effect or not? Many kids could not identify this, or also included independent variables.
Science 8 – In science 8 we continue to use the Smarter Science framework for developing experimental design. For today’s class, I started out by pouring some corn syrup into a beaker of water. The idea was to stimulate kid’s observations and wonderment about viscosity. By having a beaker with water in it, the students are reminded that corn syrup and water are probably different.
I had the students fill out a level 2 Smarter Science experimental sheet, which I plan to take home and give feedback.
For today though, I took the idea that several kids had which was to test pouring rate. This is close to a lab that is in the science 8 textbook. So while the kids followed a set experimental procedure, I think many will have come up with the overall design of the experiment by themselves with correct dependent variable, independent variable, and control variables.
Science 9 – Having previously viewed yeast budding under a microscope, students worked with me to design a new lab based on their observations.
Students noted the following observations: colour was tan, a gas was given off, there was budding, the yeast moved around (on the slide due to fluid flow).
Students then agreed that they could vary the following: amount of yeast, amount of sugar, amount of water, temperature of water, type of water/liquid, type of sugar.
From this, the experiment was designed. I had to help with the what we would use to measure or observe: by putting balloons on the flasks, the amount of gas can be compared. Students agreed to test the type of liquid (pH) and amount of sugar. This fit nicely with a lab that is written up in our textbook. Of course I was guiding them towards this 🙂
One problem with this is lab is that we have only two electronic balances for measure yeast and sugar, and our triple beam balances are not calibrated (they won’t zero properly). Measuring mass is a major time pitfall in carrying this lab out.
Physics 11 – Today we finally debriefed the lab results. There wasn’t a lot to say at this point because we had spent so much time talking about things just to get here. I really wish I could see how other modellers handle this kind of thing, I wonder what their whiteboard meetings look like?
A few things I would do next year, if I do this again:
- Force all groups to graph F vs a. While we agreed that a vs F made more sense with acceleration being the input, the analysis for realizing a general model from this is not obvious. By graphing F vs a, it’s easier to see that the slope is the system mass
- Have each group explicitly write down their system mass in kg while collecting data.
- Have a clearer discussion on how Fg = Fnet. I mentioned it, but I don’t think it resonated with the students.
Would I do this lab again?
There are three major problems with this lab. First, it took a heck of a long time. Second, not all the kids seemed to get the big picture. They got some data, calculated numbers that Mr. Smith told them to, and graphed them like Mr. Smith told them to. Some kids don’t fully appreciate the thought they put into their work. When they ask me questions like “what do I graph?”, I’ll answer with things like “well, what relationship are you trying to find? What should you graph? What should your independent variable be?”
My last statement above highlights the third problem. If they kids graph a vs F, which makes sense, then there is no obvious physical explanation for the slope. I have to explicitly tell them to change their equation to a =… (why?) or to purposely graph F vs a.
On the positive side, 2 of my 3 classes categorically thought the lab was good and recommended for next year’s class to do it. Several kids did have a solid A ha! moment, which is always good. Others said that playing with the video and analyzing the data made them appreciate how forces have a direct affect on acceleration.
I wonder if a more qualitative lab could replace this one? Something like what Josh Gates wrote about in the Physics Teacher (2014). I currently can not do exactly what he does because I don’t have the sensors, but it could be something to aim for.
Physics 11 – It was a long road, but today the students finally finished their unbalanced forces lab analysis. This took a lot more time than I had expected, and I would say that the work ethic has been pretty good. Lots of kids were getting a bit mixed up with their data and calculations, so there were several times where I would grab their data tables and quickly calculate acceleration and graph in Excel. I had thought about showing kids how to use Excel, Desmos or Plotly, but opted to stick with pencil and paper. Learning to use this kind of software would take another day of time. Heck, I even find Plotly and Desmos confusing at times.
I’m really wondering if it is worth all of this time to do a lab on unbalanced forces….
Physics 11 – Having become familiar with DMV for direct measurement, today I had the students analyze unbalanced forces as a substitute for the modified Atwood machine lab. The modified Atwood machine poses a few obstacles for understanding. First, it’s kind of hard to set up unless you have several sets of cart tracks and pulleys (we don’t). You also have to instruct students to keep the system mass the same (hand waving). You also need some decent technology to for measuring time and position (ie motion sensors or motion encoders), or your results go a bit sideways. I think ticker tape timers work quite ok for this type of lab, but only if the students have played and experimented with the timers before.
This year I wanted another try at doing the unbalanced forces lab so I went the direct measurement video path. The lab instructions were posted as seen above, and I introduced the DMV to them. To my surprise, many students continued to have problems finding the acceleration of the cart, they started collecting all sorts of data about position and time. We worked through it and by the end of the class all the groups had data, some groups had calculated acceleration and Fnet for each case, and some students even started graphing.
Science 9 – Today’s lab was to extract DNA from strawberries. What a wonderful activity to do. It’s easily accomplished with minimal expenditures, and while the students would not be able to devise the procedure themselves, the steps are somewhat understandable. Smash the strawberries to break cell walls and membrane. Soap further breaks down the cells and releases the DNA from the nucleus. Ethanol makes the DNA percipitate out of the solution. Heck, I wouldn’t even come up with the procedure.
There were lots of smiles going around the classroom today and there was a good amount of learning. It was good day at school.