Snow Physics, cont.

After a wonderful spell of blessed warmth, we are again in the grips of the demon snow. Here is another reason why I hate snow. Walking dogs in snow is a task best left to the experts. Even on a flat, horizontal surface, the danger of slipping is large, but when you have to dodge cars that have blocked the sidewalk, this puts an extra measure of danger into the situation. You must now walk on the sloping driveways and this is a three-way problem, from a physics standpoint.

1. Snow and ice have a lower coefficient of friction with shoes than does cement, brick or asphalt. The coefficient of friction can be thought of as a way of telling how large a frictional force will be encountered when one object is in contact with another. A lower coefficient of friction, means less frictional resistance. When you walk, the static friction is greater than your force applied against the sidewalk, so you don’t slide. With snow and ice, however, you meet far less resistance and it is more likely that friction won’t be able to keep you in place.




2. When you walk across a flat, horizontal surface none of your weight is directed in the direction of your motion. Your weight points towards the center of the earth and you are moving forward. On an in incline, however, that changes. Even though the direction of your weight does not change, the angle of the surface has and it sets up a situation where a component of your weight is directed downwards along the slope. Without trying, you have now set up a force that is pulling you down the slope. The steeper the slope, the greater the proportion of your weight that is acting to pull you down the incline.




3. Your center of gravity is positioned roughly in the middle of your gut. As long as that point stays above your base of support (the area bounded by your feet), you stay upright. If that center of gravity finds itself away from your base of support, you fall. Walking on a flat surface, your center of gravity stays happily above your feet, on an incline, the chance is greater that your support base will get away from your center of gravity (your body leans out away from your feet). This makes your position very unstable.

Taken in sum, all of this means that I had to endure the indignity of landing at the bottom of a neighbor’s driveway, backside down, with two dogs licking my face to make sure that I was still alive to fill their food bowl. Happy New Year….