Physics 11 – Today we moved into more quantitative analysis of conservation of energy. I was pretty pleased with the previous class and the work done using bar graphs, and kids told me that they were feeling pretty good about. Gulp, that’s often a bad sign!
I could see today that several kids were not quite making the jump from bar graphs to using the conservation of energy equation. Lots of the confusion stems from the students not knowing the beginning and end “situations.” For example, consider the question below:
A 30.0kg gun is standing on a frictionless surface. The gun fires a 50.0g bullet with a muzzle velocity of 310m/s. Calculate the kinetic energy of the bullet just after firing.
Several kids were very unsure of what the “beginning” and “end” are. They were very used to have clearly drawn diagrams given to them. This isn’t strange, research has shown that giving diagrams to students can actually impair their problem solving (I can’t find the reference just now, but I read it recently).
Physics 11 – The class had another good day today. Similar to their work on bar graphs, today the students too what they know about energy calculations and bar charts to apply them to conservation of energy questions. We had some good discussions and questions again. Overall the students competently solved problems with little intervention from me. If this is constructivism, then it isn’t always bad. Why this works in this case is that students have all the prerequisite knowledge to solve these problems and they’re ready for a new challenge. The calculations themselves are easy, and the kids are getting very good at bar graphs.
I really like this approach because it turns conservation of energy problems from applied math (Eg1 + Ek1 = Eg2 + Ek2 + Eth, solve for the unknown) to understanding energy transfers.
Physics 11 – By using the LOL diagrams, students do not need to conjure up the Work-Energy Theorem. Instead, students can use first principles: by analyzing the LOL diagram and coming up with the conservation of energy equation, students can solve for any unknown. The work-energy theorem, while concise, is one extra level of abstraction that probably isn’t needed at this point. What is more important: that a student can plug numbers into the right formula or figure out what is happening with energy in the system? These aren’t mutually exclusive, but abstractions can lead to answers with understanding. This is seen all the time in math, physics, programming, etc.
For problem solving, each step is simple and achievable but these are multi-step questions. They can be difficult for students while they learn to assimilate several ideas at the same time.
– Today my students worked on their Transfer Task for Term 2. This one was a goal-less problem. The idea for transfer tasks is as follows. The learning objectives cover the basic concepts and skills that my students should know, but this doesn’t mean they are experts. In other words, to get the very best grades in physics, up to 100%, students should do more than the basics.
With SBG, for each learning objective I ask students to answer several questions in a row with no mistakes in order to “master” an objective. For this to be a reasonable goal, I cannot ask the hardest questions. If I did, almost no one would master any objective. Coupled with this is the idea that students should have some kind of performance for each unit. Something that requires them to take what they’ve learned and do something new with it. Enter “the transfer task.”
Anyways, the video above is their homework. I’m asking them to be proficient in conservation of energy questions and we’ve already spent significant class time on this. For those that need help, I’ve made this tutorial video.
Physics 11 – This photo shows a fantastical graphical representation for energy and conservation of energy -> the energy LOL diagram.
Students get pretty good with this representation after a while, but it takes time. So my question is, how well do physics 11 students really understand conservation of energy if they skip this representation and go straight to an equation such as delta E = 0. If it takes a few days for students to really nail the LOL chart, then are other students primarily doing plug’n’chug on conservation of energy problems? How can working with an equation offer a better conceptual understanding than a simple bar chart?
Some of the thinking used with LOL diagrams is similar to force diagrams. First you need to draw and label a force diagram (or LOL chart) and from it you derive the Fnet equation (conservation of energy equation).
One thing I’ve noticed with the LOL charts is that many students have a mental block going from the graphical representation to an equation. It’s not the math that is hard or the concept, it’s that they are thinking too far ahead. If students were asked to calculate some energies in the example above, they can get roadblocked if they don’t immediately see how each item would be calculated. There is definitely some process skills that need training.
- find the conservation of energy equation, don’t worry if you don’t think you have all your values
- write down what you think you know
- see what other things you can calculate
- can you now find the thing you’re looking for?
The above process requires patience and methodical attention to detail. It’s not memorization, it’s not categorization, it’s understanding and practice.
Physics 11 – I was introduced to energy bar charts through the physics modeling program, and it is one of the best things that I’ve introduced to my students. So much of the conceptual material for energy in physics 11 is covered with these bar graphs. All that is missing is the algebra and calculations.
The students were really engaged while working through practice questions on bar charts. I think this work really hits the sweet spot for the Zone of Proximal Development for the majority of students. The charts are new, thought-provoking and manageable.
I have been following the modeling curriculum fairly closely until now. I’m not equipped to do any experiments with energy. Rather, I’ll be use direct instruction that that the area under the curve of a Force-Displacement graph is energy. This will lead into the concept of working, and the formulas for gravitational potential energy and kinetic energy.
Physics 11 – Energy has been introduced in physics 11. So far the students are focusing on the idea of energy storage systems as opposed to something “having energy.” I used a couple of quotes from Richard Feynman to stress that we have a really hard time describing exactly what energy is, but we are not bad at saying where energy is stored.
It is important to realize that in physics today, we have no knowledge what energy is.
Do not keep saying to yourself, if you can possibly avoid it, “But how can it be like that?” because you will get “down the drain,” into a blind alley from which nobody has yet escaped. Nobody knows how it can be like that.
The students were really engaged during this activity and the students demonstrated good critical thinking. Without detailing it, this work touches on both the First Law of Thermodynamics (the total amount of energy doesn’t change) and the Second Law of Thermodynamics (Dissipated energy never goes down).