The Physics of Hydroplaning

             Like many of my fellow Colgate students, the recent torrential downpour caused me to freak out a bit. The water has surrounded my apartment, soaked my backpack and ruined my shoes on my walk back from the library. What I found most worrying about the rainstorm was, however, the impact it could have on my car. I had to move my car from its original parked location, because the parking lot was flooding. While I was moving my car, I started to wonder whether or not I was at risk for hydroplaning.

           

           Hydroplaning occurs when a car’s tires are prevented from making contact with the ground due to the presence of a layer of water. Thus, hydroplaning only occurs when there is a significant amount of water on the ground. The speed of the car, however, plays a critical role in hydroplaning as well for cars typically only hydroplane if they are traveling at a speed of over 50 mph. Why is this?

           A car that is moving fast provides less time for the tire to dissipate the water underneath it causing a greater accumulation of water around the tire. As more water starts to collect under the tire, the force of the water on the tire increases to the point where the force of water is greater than the downward force of the car and the car is lifted off the road onto the water. This lift causes the tires to be unable to make contact with the road.

           The loss of contact will the road eliminates the frictional force between the car and the road. This force of friction between the car and road is the force that allows the car to move forward on the road. Thus, the complete loss of this frictional force will cause the car to slide uncontrollably. The coefficient of friction between a tire and a wet road is 0.4. My car, a Prius, has an average weight of 1325 kg so a complete loss in the friction between the tires and the road would cause a rapid loss in force of (1325 kg) (9.8 m/s2)(0.4) around 5194 N! Luckily, I was driving at a speed of 20 mph so I was not at a great risk for hydroplaning. To stop a car from hydroplaning, drivers should slow down and avoid driving on super slick roads.