ABSTRACT
As we discussed in the introductory chapter of this book, friction played an important role in ancient and medieval physics, somewhat similar to the force of inertia. These two forces-inertia and friction-cannot exist without each other. To put it simply, if friction existed without inertia, nothing could move, whereas if inertia existed without friction, nothing could stop. However, Aristotle’s Physics lacked a correct understanding of both friction and inertia. Aristotle believed that a body keeps moving only when a force is applied and that velocity is proportional to the applied force. He also believed that straightforward and circular motion are two unrelated types of motion, as well as terrestrial and celestial motion, and that motion and rest are two unrelated states, leading to numerous contradictions in his concepts.
