physics observation

This weekend I was in the car driving to the store when I suddenly saw a speed limit sing that said 25 m. p. h. because of the construction that was going on in there. Since I was at a higher velocity I had to decrease the velocity of the car and stay constant at 25 m. p. h. I knew I was at a constant velocity because I was not going faster or slower. I also noticed that a car that was next to me was pulling ahead of me which meant that it was going at a faster velocity than me. Later on, I saw a stop sing and I had some books on the seat that was next me, at the moment when I stopped the car the books moved and dropped. I knew the explication of that was acceleration, because since I was going at a constant speed and then I suddenly stopped, the change of velocity and acceleration made the books go down to the floor of my car. This relates of what I've learned in class because now we are learning how the constant velocity affects an object to move.