In other words, Kepler's laws do not deal with the cause that makes the planets move that way. The force of nature that constrains planets to follow these rules was discovered by Newton. His most famous book is called Principia was published in 1687. In his book he discusses his three laws of motion as well as the law of gravity which we will discuss later. But first let's introduce Newton's 3 laws of motion.
Examples are, either a book sitting at rest, or a car moving with constant speed in a straight line.
Let's try first to understand the notion of a force. From all these examples we notice that a force creates a direct pulling or pushing effect. Also, the direction that a force acts, is important because it controls the direction the object will finally move in. We do not see forces. We see the effect they have on the objects they are applied.