Question

In terms of vectors why does an object slow down? (physics question)

Answer 1

An object will slow down if a force vector suddenly appears in the opposite direction to that of the movement of the object.

Answer 2

The force of friction opposes the motion of an object, causing moving objects to lose energy and slow down. When objects move through a fluid, such as air or water, the fluid exerts a frictional force on the moving object. The frictional force from a fluid is called a drag force.