Under normal driving conditions, which type of friction helps to slow your vehicle?

• A. Kinetic
• B. Rolling
• C. Static
• D. Fluid

Answer: (C)

The decelerating force during normal braking comes from static friction between the tire tread and the road. When you brake, the wheel slows but the tire stays in contact with the road without slipping, so static friction resists that motion and provides the stopping force up to its maximum value. This is why you feel the car slow smoothly as long as the tires maintain grip. If you brake so hard that the tire slides, you’d get kinetic friction, which is weaker and slows the car less efficiently. Rolling friction or air drag are much smaller contributors to braking under normal conditions.