Ever read a book? Well let me rephrase that for some people.... ever read a couple pages out of a book pretendding to read the whole thing for english class? Well guess what my friend, not only have you practiced Physics, but you demoonstrated Newton's 1st Law of Motion as well!!! When you open the cover you are applying a force onto the book's cover. A force is defined as a push or pull on an object. Hence, when you pull open the cover and then push it down you are applying a force to it. When you open the cover and hold it vertically, there is a net force becuase the force from pulling the cover open is greather then the force of gravity. In other words the external forces applied to the book do not cancel eachother out. When you remove your hand, the cover of the book falls, this is because gravity is the only force acting upon it if a book sits in a locker remainig untouched for a month is there still a force upon it? Well there are forces on it but there is no net force, this is a state known as static equilibrium. In this 'locker state' all the forces are balanced. The force of the locker pushing up on the book is equal to the force of gravity pusing the book down. And as you know, if this locker were to magically disappear then the book would fall because now there is net force because there is nothing to balance out the downward force of gravity. So the book would simply fall down untill acted upon by another force such as the ground which would then again change the net force to zero by balancing out the force of gravity. let go back to the concept of reading (or 'skimming' through the book) The pages of the book do not magically turn themselves. You have to apply a force to them (because an object at rest will remain at rest until acted upon by a net force) That net force is your hand. When you flip the page (and that's hard work right there) your hand is facing inertia- the reistance from the page of this change of velocity. Or simply put the mass of that single page, is the amount or resitance you hand is facing. This just goes to show physics is everywhere