[JoeAltmaier]

My favorite wrong fact was the simple model of friction we were taught - that force was proportional to surface area and weight. In middle school we were given force gauges and wood blocks. Pull them stacked or linked and graph the force vs weight X area. I got a weird curve. Looking around, I saw everybody else fudging their data to make a straight line. Confusing.

Decades later I heard on the radio "The traditional model of friction has been proven incorrect for many materials" and I thought, I knew that in middle school.

[JupiterMoon]

I think you may have misunderstood something here. The high school static fiction model is:

  frictional force = normal force X coefficient of friction

i.e. frictional force is independent of surface area according to this model.

[JoeAltmaier]

What are the units of that coefficient? Per square? And are we talking force or pressure. Hm.

The experiment used blocks with hook-and-eye screws. You dragged them across the surface linked in a chain, then again stacked, in twos and threes. The result came out nothing like a linear relationship.

[marcosdumay]

The coefficient has no unity. It's N/N. And we are talking about force, not pressure.

By an ideal linear friction, you should have measured the same force on all experiments. But reality is way more complex, and sometimes the ideal model won't give you even a first order approximation.

Your teacher shouldn't have used wood blocks (unless he wanted to make a point), metal ones would give better results.

[JupiterMoon]

I'm sorry you've got totally the wrong end of the concept here.

Check out https://en.wikipedia.org/wiki/Friction#Dry_friction