How is the net force calculated

The net force is calculated by subtracting the smaller force from the larger force. The end result will be the net force. The net force can be effected by friction which lowers the velocity and slows the acceleration or the movement forward.

Velocity- the rate of the change in an objects motion.

Friction would be like when you roll a marble across tile then it hits carpet and almost completely stops.
Or when a car brakes after going fast and the tires slide on the concrete but slow the car.