## Day 88 – Lab Practicum

Physics 11 – I divided the class into  random groups and each group was given a bucket with three masses, two Newton scales, and a wooden block.  Their task is to determine the coefficient of friction between the floor and the wooden block.

Most groups were content to take one measurement and use that to calculate the coefficient. I stepped in a bit and suggested that they get more data. I did this by asking them what their independent and dependent variables could be, which helped.  Some students even showed understanding of how they could use a graph to help determine the coefficient, while others were happy to average a range of numbers.

Overall the activity went ok.  They were asked to hand in a good lab report, which will then be graded. They previously handed in a lab report which I gave them feedback on. Hopefully they will take my feedback and use it to do a good job on this one.

## Day 84 – Friction

Physics 11 – Today’s lesson is typically one of my favorites for the year.  Students brainstorm factors that affect friction and then they test out their ideas.  In the past I let the students have all the say in their work.  However, last year I noticed that several groups were doing pretty crazy stuff – mostly they weren’t measuring forces at all. In other words, they weren’t clear on what was the dependent variable in their experiment.

So this year I gave them more structure:

This helped with the experimental design but there was an unintended consequence.  The students gave up their agency. The day became more about me.  In general the students were asking “what do I do next?” and saying “I don’t know what to do.”

I’m not sure what I will do next year. If I had more time, I would run through the above sheet on a different experiment, and then let them figure it out for the friction inquiry.

Here is a link to the above Friction Experiment document.

## Day 79 – Friction Inquiry

Physics 11 – Today was one of my favorite lessons for the year, where students propose things that affect friction and then carry out their own experiments to answer the question “what things affect the force of friction?”

This group’s work was pretty good, I especially like their force diagram. Yes, surface materials affect friction.

Here’s another group’s results. Check out the sweet bar graph.

One of the more surprising results: velocity does not affect friction. This group did a good job in carrying out an efficient test. They knew that they didn’t have to measure velocity, they only needed to use two buggies that clearly had different velocities. They also were clear that what they really had to measure was force.

Two groups working on surface area had different hypothesis. The above group is the first time that I’ve had a student predict that surface area would not affect friction, and he managed to convince his group of this prior to them carrying out their test. That was pretty cool.

Mass affects friction. I drew points on their bar graph to emphasize what looks to be a linear relationship. I had encouraged them to do an x-y graph but they went with a bar graph.

One thing that I noticed a few times was groups being confused on what to measure.  It’s possible that only 1/2 of the students were able to design the experiment while the other half listened and were convinced by their peers on what to do.

One group was supposed to see if velocity affected friction and they concluded that it did. However, we noticed that they only tested one velocity.  Other groups were correctly dealing with their experimental variable, but were measuring time or distance instead of force. I will spend a day working through Smarter Science with them…

## Day 72: Friction Lab

Physics 11 – Ok, they’re not the greatest photos in the world, but you get the idea!

Today students conducted the experiments that they designed last class.  A few groups still did not see that they should be measuring force directly in order to find friction.  However, most groups were reasonably efficient in collecting enough information in order to determine if their test variable had any effect on friction.

One of the variables that is a bit more difficult to test is object speed.  Moving a wooden block at different speed gives some variability in measured friction.  I think this is partly due to the students’ experiments which have the blocks moving very slowly. In these cases, you can see that the blocks are moving in and out of static and kinetic friction.  It was very cool to see some groups clearly state that they thought the friction changed depending if the block was moving or not.

The students did not do a quantitative lab for finding the coefficient of friction, for this activity it was enough to see if there was an effect or not.  I think we will do a quantitative lab as an assessment for lab skills.

## Day 70: Inquiry into Friction

Physics 11 – We used most of the class to look a how friction could be modeled on the microscopic level, and the factors that affect friction.  The first class brainstormed possible factors that affect friction and then broke into groups to investigate a factor.  However, a few groups had a difficult time clearly identify friction force as the dependent variable, and a variable that they could directly measure.

I had the second class work through a more structured approach to designing their experiments, where the dependent variable was more explicitly stated and recognized as being something that could be measured. We used the Smarter Science framework to assist with this.  We didn’t have time to carry out the experiments, so that will be done the next day.