Introduction: It's hard to imagine, without careful thought, what causes a vehicle to remain moving without flipping over while traveling on a road that has a lot of friction. That is, unless free-body diagrams are used. Free-body diagrams are diagrams that visualize the forces acting on a given object. These forces can include, but are certainly not limited to, frictional forces that act horizontally, the weight of the object that acts vertically downward, and the normal force 

that acts vertically upward.

Frictional force can be calculated using the following equation: [math]F_f=µF_N[/math], where [math]F_f[/math]=frictional force, [math]F_N[/math]=normal force, and [math]µ[/math]=coefficient of friction

In problems that involve friction, it is important to understand that a car slowing down could be represented by a balance between the normal and gravitational forces, while the length of the arrow representing friction would be greater than that of the force relating to the acceleration of the car over time. Therefore, in this case, the net force on the car would be directed opposite to the direction of motion, implying that the net force was negative and hence, the car had a negative acceleration. In this case, the car would be decelerating, or slowing down. This example shows one of many applications of free-body diagrams to understanding the forces acting on an object.