Egg Carton Friction MOdel

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The Premise

For years, I struggled to help students visualize friction in a way that supported their understanding on a microscopic level and led to a deeper understanding of why static and dynamic/kinetic friction are different.

Then I saw this awesome idea posted by Bree BarnettDreyfuss (@BarnettDreyfuss) about using packing foam as a model for surface contact. I love that this is both tactile and visual but I didn't have any of that sweet foam on hand so I improvised and realized that I had tons of egg cartons! :) Basically a cheap knock off on a much cooler set up...

One of my favorite visuals for talking about microscopic surface contact for friction. You see lots of head nodding and invisible light bulbs going off.□□ pic.twitter.com/6zoK8poimM

— Bree BarnettDreyfuss (@BarnettDreyfuss) September 20, 2019

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The Set Up

The set up for this model is really cheap and easy so it's possible to use as a demo in the front of the class or a manipulative for each group in the room. Basically all you need is two empty egg cartons. I like one of them to be an 18-egg carton because it's wider and does a nice job of representing the table or the floor but this would work with two 6-egg cartons as well

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The Model

After a short discussion about how models can help us better conceptualized topics but may not be perfect in every way, I have my students imagine that they are able to zoom in on the contact boundary between an object and the table. 

When the object is at rest, the microscopic features of both surfaces "settle in" to each other kind of like the nesting of the two egg cartons. Overcoming this microscopic interlocking requires a certain amount of force but once the object has "risen above the grooves", as long as it keeps moving it is able to skirt along with less resistance than that initial scenario. This is analogous to static and dynamic/kinetic friction and is a nice conceptual starting point before collecting data and quantifying this properties with numbers.

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CLICK HERE FOR MORE DEMOS!

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