On page 94, there's a diagram with a cart on the top of a loop. At the bottom of the page it says:
Example 6.5: In the previous example, if the net force on the car at its topmost point is straight down, why doesn't the car fall straight down?
Solution: Remember that force tells an object how to accelerate. if the car had zero velocity at this point, then it would certainly fall straight down, but the car has a nonzero velocity (to the left) at this point. The fact that acceleration is downward means that, at the next moment v will point down to the left at a slight angle, ensuring that the car remains on a circular path, in contact with the track.
In the last statement, should't it be down to the right at a slight angle because acceleration is directed toward the center of the circle the entire time?
In case you don't have this book, the cart enters the loop from the left to the right.