Unit five opened up with Newton's Laws of motion. I no longer print out the slides and post them on the covered sidewalk posts. Instead I share a Google Slides presentation of Newton's Laws ahead of class. The students can then follow along on their own device. The presentation of Newton's first law, done using a RipStik and a four square ball, is plagued by the external force of friction, which provides a segue to laboratory five and the investigation of the force of kinetic friction.
Cordny and Ivan explore the impact of surface area on kinetic friction with a stack of eight glass sleds.
Mike's students join the class to have a look at the periodic table.
Cordny working with Ivan.
A-ann and Marmayon investigated the impact of grit. Their data was perhaps some of the most consistent grit data in the history of this laboratory. The result has always statistically been no effect, with a possible exception of an increase in friction for the glass sleds on the 1500 grade sandpaper.
This term I had them use a wood sled with a 200 gram weight on top of the sled.
The 200 gram weight allowed them to work with the green spring scale, freeing up blue scales for the weight groups. Each term I tend to forget one detail. This term the detail was that the group working grit needed the grit conversion data sheet. As the course is paper free, this would mean sharing the grit conversion data digitally.
The current complication is that the grit data is in a Google Sheets data collection document, but the students are working in Desmos. App switching Sheets to Desmos is a suboptimal solution for obtaining the grit sizes. Perhaps pre-marking the grit sizes on the sandpaper would work. The grade is problematic as the grade is a measure of grit per area, and the values are non-linearly related grit size. This is a laboratory that would still benefit from a reference sheet showing the relationship between grade and grit size.
One possible solution is that the grit size in micrometers is essentially equal to 13800 ÷ (grade - 9.3) for grades 36 to 1500.
The wood block sled, weight, and spring scale combination proved propitious in that their results were very consistent.
Data for the new material, a block of PVC board seen in the background. The students often enter data directly into Desmos.
The students can see the linearity of the data develop as they take the data.
Desmos is also available as an app. The app has the advantage of working off line.
Joanalynn enters data while Benalyne takes measurements of the effect of weight on the force of kinetic friction for a moving wood block. Three groups worked on weight, each with a different material.
The PVC board is essentially a chunk of plastic.
A third group measured the effect of weight on force of kinetic friction for a glass sled. The sled is a piece of a glass louver.
L-Jane records weight data.
Marmayon pulls the wood block while A-ann holds the sandpaper. The equipment for this laboratory is locally available with the exception of the spring scales.
Darx recording measurements made by L-Jane
Piruno makes measurements of the force of friction on the PVC board
Holding the sandpaper is necessary. The students are attempting to measure kinetic friction - the friction opposing motion at a constant velocity. This rig is not useful for measuring static friction. Explorations of static friction often involve the use of a inclined plane to determine the angle at which a block starts to slide. This is then translated to the force of friction using trigonometry. For students who have not had trigonometry the mathematics is opaque. This laboratory generates data that can analyzed using the mathematical techniques the students have been using since the first laboratory - the use of
Desmos.
The grit data gathered by A-Ann and Marmayon would yield a consistent 250 gram force for all grits.
Benalyne checking data recorded by Joanalynn
Left board at class end: lab set-up.
Right board at class end: Lab wrap-up on the right. The left side is laboratory four analysis.
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