We use models a lot in physics, which basically means that we try to look at situations in as simple a way as possible. We will often neglect friction and/or air resistance, for instance. In many cases this is fine, but not always. As we move through the course we will discuss ways to make our models more sophisticated.

Let's start with as simple a situation as possible. An object is floating motionless in interstellar space. There are no other objects around for billions of kilometers. Draw the free-body diagram of this object.

Our object has essentially no interactions with anything, so the free-body diagram shows no forces at all. What will happen to this object?

The object should remain at rest. Its motion should not change.