WASHINGTON, November 28, 2014 — With winter weather back in the forecast, it is important to know how to drive on slippery roads. Drivers can benefit from understanding more about what happens with their vehicles in winter weather.
A physicist would start such explanation by modeling a vehicle as a simple cube experiencing rolling friction due to its wheels. This cube encounters varying friction as it makes its way down the road, slowing the vehicle and requiring the driver to periodically accelerate and decelerate. When encountering an uneven change in the surface of the road, one side of the cube accelerates differently than the other, so the vehicle is pulled to one side of the road.
The vehicle is essentially a dumbbell-shaped object, where the two sets of tires are joined together by a “bar,” i.e. the car body. The vehicle can be also be modeled after a dumbbell-shaped object to help better explain what is happening when the car is turning.
If a driver wants to speed up or slow down, the driver pushes on a pedal to add or subtract, rotational force, torque, to the tires. With this torque comes another “force” that “pushes” the vehicle left if the car is acceleration, and right if the vehicle is decelerating.
When the tire surface is flattened against the road, the rubbing of the tire against the road creates friction. The rotating surface of the tires encounters rolling friction from the road which causes the vehicle to slow,and sliding friction helps the vehicle stay on the road. Sliding friction is what prevents a tire from sliding right or left.
With the addition or subtraction of torque, as well as changes in direction due to steering or the vehicle going around a curve, the “pushing force” of the torque on the tires can become greater than the sliding friction of the road. If the road lacks enough sliding friction to keep the vehicle on the road, the dumbbell-shaped vehicle starts to slide and spin instead of going straight.
In other words, improper acceleration in its various forms is what causes accidents when the roads are slippery. Drivers, therefore, need to go slowly when there are slippery road conditions, because it gives them more time to properly accelerate, especially around a curve.
That said, going up a hill too slowly in the winter can also throw a vehicle off the road since drivers must add extra torque to their tires to push the vehicle up the hill and maintain their speed. Consequently, driving on slippery roads requires a constant effort to consider how fast the vehicle is accelerating.
For those who live in areas where winter weather is common, a high quality set of snow tires should be considered a necessity as they boost sliding, as well as rolling, friction. For these individuals and all others, driving safely on a slippery surface means becoming aware of how quickly they accelerate.