And even to the bad ones.

People in this area generally don’t know how to drive in the snow. The generally slow clearing of snowy conditions definitely does not help, but folks just aren’t helping things by sucking at driving. Between the time I was excavating my car and the recent trudge over to a local fast-food restaurant (I won’t blatantly advertise the chain — for free — but according to Concrete Blonde, their iconic spokesperson is going to die tomorrow), I have seen and heard dozens of people slip and slide their tires over the snow and ice.

Today’s public service lesson is Friction.

The details of friction on the microscopic level are quite complicated, but the general idea is this: the frictional force is proportional to the normal force (N) on an object. The normal force is that force the surface exerts on it, so for an object which is not accelerating vertically, the normal force and weight (W) cancel (the net force being zero). The proportionality constant for the frictional force (f) is the greek letter mu; I’ll just use u since I don’t want to muck around with LaTex. f = uN (Who said physics isn’t fun? It says it is, right there!)

It turns out that there are two categories of friction: static friction, for when an object is moving, and kinetic, or sliding friction, for when two surfaces are moving over one another. Generally speaking, the coefficient of kinetic friction is smaller than that of static friction, and the implication of this is that (all things being equal) once two surfaces start to slide over each other, they will continue to slide. They won’t suddenly “catch,” unless there is a change in the surface conditions.

So when your tire starts to slide on the snow or ice, or any other surface for that matter, it is going to continue to slide. This is the concept behind pumping your brakes when you start to skid, and the reason that anti-lock brakes are a popular safety feature. Once you start to slide, continuing that action is the wrong thing to do, much less gunning your engine to make the wheels spin really fast (coefficients of friction can decrease with speed, and melting the snow makes for a slipperier surface). Your best bet is easing up off the gas and starting over. Rock back and forth a little so there’s some momentum, and you don’t need quite as much force to get going faster. Once you start to skid, you’ve lost.