Monday, February 9, 2015

Slow down to avoid disaster

Decades from now the few who have the aptitude to read and the motivation to study history will be incredulous that people used to drive individual  un-linked vehicles.

"How could that possibly be true?" they will muse. 

By then light rail will handle most transportation and "automobiles" will no longer be autonomous. They will be sensibly guided by computers that will also record locations, trips, driving habits, and other personal information.

Meanwhile, drivers have lost any knowledge they ever had about the Newtonian physics that govern how wheeled vehicles operate on snow, ice, and other low-friction surfaces.  Think back to high school:  an object in motion tends to stay in motion, an object at rest remains at rest; all of that stuff that your insane physics teacher directed at you without any context.

Sir Isaac Newton, a pretty unpleasant and strange character, and also a genius, created experimentally verifiable theories of gravity, motion, optics and even invented calculus. So independently did Gottfried Wilhelm Leibniz.  Somehow mathematicians chose Leibniz's confusing notation.

Among Newton's accomplishments were his "laws" of mechanics, such as Force equals mass times acceleration; mass times velocity equals momentum, and the idea that potential energy was converted into kinetic energy at the rate of one-half of the product of mass and the square of velocity.

Newton also linked the dropping of apples (as the story goes) with why the moon orbits Earth, and correctly described the inverse square law of gravitational attraction and calculated the gravitational constant of Earth at 32 feet per second per second. 

These relatively simple laws were sufficient  to solve artillery firing solutions and guide Apollo to the moon and back. Albert Einstein's equally revolutionary theories of relativity supplanted Newton's laws, but many engineers and scientists continue to use Newton's far simpler formulae. Einsteins ideas take over at very high speeds and enormous masses.

Fortunately, cars cannot travel at even one millionth of a percent of the speed of light, because drivers apparently do not understand or appreciate that their vehicles must conform to the laws of physics. No, driving a 2-ton sports utility vehicle does not protect the driver from losing control on ice or allow him to stop any faster than a conventional car. 

The brakes of four-wheel drive vehicles are no more resistant to "slipperiness" than a two-wheel drive car. Moreover, even if they could, a vehicle that weighs double takes correspondingly higher forces to start and stop. 

Yet light trucks glide past you insouciantly on the interstate, spraying your windshield with sand, salt and slush. The sand is spread to increase friction between tires and road surface.

There are two types of friction: static (for example) would be pushing a heavy box down the driveway, and dynamic, the friction that rotating wheels experience. 

The odd properties of water further complicate winter driving. The melting point of frozen water drops under pressure. A car's mass, or weight, melts the surface of an ice patch, reducing the frictional coefficient of the ice.

Which is to state the obvious. Driving  safely on ice or snow simply requires a slower speed. That's all, basically. Simple. 

Problems can arise if the car's brakes lock, changing dynamic friction into static, and causing a skid. To avoid a skid, drive slowly and slow down before trying to stop. 

Ultimately, to avoid accidents, collisions, injury and so on, just drive slowly