Gravity Makes Friction Possible

• When one drives a car, the traction of the car's tires on the road is what allows the car to move forward, make turns and stop. The less traction the tires have, the more prone they will be to skid on turns, spin while accelerating or slide across the ground when putting on the breaks. Traction is influenced by two main factors: gravity and friction. In many ways, gravity is the most important factor for traction, since without gravity there would be little or no friction. Basically, gravity gives objects weight, and the more weight that is put on a tire, the more traction it has. In the absence of gravity, tires would not be able to grip the surface of the road to propel the car forward. In such an environment, the tires would spin, but the car wouldn't move.
  
  

Friction Gives Cars Traction

• The more mass a car has being acted upon by gravity, the more weight it has and therefore the more potential exists for friction. Friction is a force that resists horizontal movement of two surfaces that are in contact with one another. In the operation of a tire, friction is the amount of force that the tire can exert onto the surface of the road when rotating. Since a tire is in contact with the ground due to gravity, it resists moving or slipping due to friction. If the torque of an engine is too powerful however, the force can cause the surface of the tire to spin relative the road, decreasing friction, and therefore traction.
  
  

Factors That Affect Traction

• Many factors can influence friction between a car's tires and the surface of a road. Changes to the amount of weight exerted on a tire alter friction and hence, traction. For instance, going around a sharp turn may shift a car's weight in a certain direction, which can increase traction on some tires while decreasing it on others. Loading a car with passengers or cargo also increases traction due to the additional weight. The surface of the tires and road also play an important role in determining traction. A normal road and rubber tires tend to grip each other well and resist sliding more strongly, meaning there is more friction and better traction. Tires have less traction on roads covered in ice, mud or water. Good traction is achieved when the road is made of a rigid material with an irregular surface which has a large amount of exposed surface area for a softer tire to make contact with and grip, such as concrete or blacktop. On the other hand, surfaces that are not rigid enough, such as mud, sand or snow, have bad traction since they can easily deform, which reduces the amount of friction.