Our car slows down due to its interaction with the surrounding road. In the absence of interactions with the environment, object do keep on going forever. Also, an object at rest will stay at rest unless its environment exerts a net force on it . This statement is known as Newton's First Law . It took people from 350BC to about 1600AD in order to figure it out.
Objects tend to resist changes in their motion.
And such interactions are described by forces. Newton's Second Law Galileo and Newton realized that an object's velocity does not change unless its interactions with its environment result in a net force. Forces cause acceleration. All that matters is how strong is the net force and in what direction it acts. We know from experience that the answer depends on the object.