Hurrah, we come to the end of the module! We started with a very simple situation. We said that there is a book on a table, and the book is not moving. We asked if there are no interactions at all.

We now know that there are lots of forces that are acting on the book! The forces are acting in opposite directions and cancel each other.

For example, the Earth is trying to pull the book down. At the same time, the table is pushing the back up. As these forces are balanced, the book doesn't move.