Background
Isaac Newton is generally regarded as one of the greatest scientific minds of all time. He ushered in the modern age of physics and mathematics - having both formulated laws of motion and gravity correctly for the first time, and having invented calculus to use and test those laws. Those two topics are only a small part of his life's work. Besides his innumerable contributions to mathematics and science, he wrote more on religious topics than on the other two combined. Consider this the next time you want to make an excuse about not having had time to finish your homework! For a biographical sketch, see the Wikipedia site below.
Motivation
Take note that this is really our first discussion of physics. All the kinematics we did is really just establishing definitions between kinematic variables while getting practice doing the associated math. Physics is, however, ultimately concerned with investigating the laws of nature, and this is our first discussion of the laws.
Isaac Newton wrote three laws of motion in his 1687 work titled Philosophiæ Naturalis Principia Mathematica (a Latin title meaning Mathematical Principles of Natural Philosophy), and yet you'll notice that he really only needed two laws and not three. The first law is ultimately a specific case of the second as you'll see soon. This was likely done so that the less mathematically inclined readers of his work would not escape the revolutionary implications of his new laws.
I might note here how I think it would be nice if physics were still called natural philosophy. If you don't care much for etymology (the study of word origins), realize that philosophy literally means the love of knowledge. Therefore natural philosophy would be the love of knowledge about nature. I hope that at least at moments during this course that you love filling your mind with knowledge about nature.
If you ever feel discouraged while trying to understand any of the knowledge that man has amassed over the past few millenia about nature and mathmatics, consider a quote from one of my favorite professors who passed away too young at Purdue University where I studied. One day he was walking past the physics lounge area and saw my good friend and me looking discouraged while studying for exams. He looked at my friend and simply said this: "Mr Abdullah, the vast sea of knowledge that lies before you is indeed finite." After many years of doing physics I have often gotten a glimpse of the edge of that finite sea. In the area of my specialization (theoretical biological physics), I even made it to shore and rested on the beach for a moment. Nature has endless mysteries waiting to be solved, and man in this respect knows little. I maintain that keeping your pride in check is always a healthy practice, and this perspective should help you do so.
Motivation
Forces
Newton's laws of motion are a description of motion related to forces that act on objects. We will now move on to discussion of forces in nature.