*Physics 11* – A couple of oops in the pictures above… First, the dreaded twisted slinky. This is annoying but I sort of get why it can happen. The quiz however is much harder to understand. What is it about my teaching which allows even one student to have such little understanding to make the mistakes shown above? Sometimes teaching can be frustrating. It’s a constant puzzle to figure out what went wrong. I guess this is the intellectual challenge that keeps it interesting.

# Tag Archives: energy

# Day 106 – Energy Transfer and Bar Charts

*Physics 11* – Having sorted through pie charts, played with the Phet Energy Skateboard Park, and given a worked example, students were put into groups and each group was given a different situation to analyze in terms of energy transfer. We then got together for whole class discussion and exhibition of worked solutions.

Some great observations by students

“Since there’s friction, shouldn’t some of the kinetic energy transfer to thermal energy?”

“On the left side you have 5 bars but on the right side you only have four.”

All in all, very good classes today.

# Day 104 – Energy Skateboard Park

*Physics 11* – After a two year hiatus, I returned to the Phet Energy Skateboard Park. This was the student’s first exposure to energy bar charts, after having spent a class on discussing energy as storage systems, and representing energy storage in pie charts.

The handout in the picture above has some leading questions for the kids to use while exploring the simulation. They didn’t hand in the worksheet. Instead, I used some plicker questions to check their understanding.

# Day 112 – LOL Instead of Work-Energy

*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.

# Day 104 – Calculating Energy

*Physics 11* – Today I was away from class again so a TOC came in to cover. The main task for the day was for the physics students to learn how to calculate kinetic and gravitational energy.

Ideally I would like students to work through this by doing two experiments, having already learned that Es = 1/2 k x^2

- launch a spring loaded cart using different springs and measure the speed that results
- launch a spring loaded cart up a ramp using different springs and see how high it goes

Both of these activities really require a decent cart with spring (ie little friction) and a motion sensor for the speed. Especially for task #1 we would need a decent computer for quickly graphing the data and manipulating the graphs.

This kind of activity would take at least two classes and probably three. The question I wonder is whether it’s worth it. Research says yes but it’s also about value systems. We can spend a lot of time going deep on topics and using good process skills, or we can move through the topics quickly and maybe work on some interesting and creative (engineering) projects.

# Day 98 – Energy LOL Diagrams

*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.*

# Day 89: Working on Work

*Physics 11* – Working on Work was the topic for the day. We had discussed in class how working is the idea of transferring energy into a system. As well, I had introduced the idea that energy is the area under a Force-displacement graph. From this, it was relatively easy for the students to grasp that W=Fd.

The formula itself is easy to grapple with. However, the nuances need clarification. So went through 4 examples to illustrate 4 main points:

- Work is calculated from applied forces, not a net force
- Something has to move in order for there to be work. I briefly explained that even a transfer of heat is a type of work, where the “thing” that moves are all of the particles (as per the Kinetic Molecular Theory).
- We only need to consider the component of the force that is in the same direction as the movement
- Work, while being a scalar, can be represented as a negative quantity which refers to a transfer of energy out of a system.

After going through the examples, the class then did some Peer Instruction with Plicker cards. One class went from 50% correct to 98% correct. The second class improved but still need an intervention – it went from 40% correct to about 60% correct.

I won’t use this question again, though. There is in fact a small bit of horizontal force acting on the mass equal to the force of friction between the mass and the hand. If μ = 0.1, then Ffr = 0.2 N, and the work done would be 0.4 J. Only a few students asked about this, so I guess for one more year I avoided confusing too many people.