Tesla must be testing me. First there was this failed Armor Glass demo at last week’s unveiling of the company’s Cybertruck prototype. Now it's this tug-of-war between the Cybertruck and a Ford F-150. An uphill tug-of-war!

It looks impressive. But this isn't a battle of horsepower or torque—it’s a battle of mass. As long as both vehicles have sufficiently powerful engines, the heavier one will win. Why? Because it's all about friction, where the rubber hits the road. The Tesla Cybertruck, with its steel shell, is probably more massive than an F-150—and, for environmental and other reasons, that's not necessarily a good thing.

To keep from getting fooled by stunts like this, you gotta know the physics. Let's see what's really going on.

Here's the Rub

Friction is pretty complicated. You have all of these atoms on the surfaces of two objects that are interacting with each other—that's not so simple. But don't worry, there's a fairly easy way to model this interaction. Here is an expression for the magnitude of a frictional force between two non-sliding (or "static friction") surfaces.

Illustration: Rhett Allain

I'm going to go over each part of this model, but first how about a demo? Take a book or block or something similar and put it on a flat table. Now push on it from the side—but not so hard that it moves. Here, like this: