When it comes to Newton's 1st Law, the two situations it describes are not equally understandable by many beginning Physics students. One part (an object at rest stays at rest) seems straight forward enough. If an object is just "sitting there" and I do not disturb it in any way, it is not going to suddenly start moving (i.e., suddenly accelerate from rest).

However, the second part of the 1st Law (any object in constant motion stays in constant motion) can sometimes be tricky to grasp. Don't all objects "left alone" eventually slow to rest? Or, are such objects actually being "left alone"? The key is to consider the NET FORCE (the sum of all forces) on an object rather than any single acting force.

IN THIS THREAD: Please give an example in your personal experience of an object in constant motion (i.e., moving but NOT accelerating in any way). Give a description of all the forces acting on it as it moves, and explain why, despite having forces act on it, it still does NOT accelerate. As before, no two examples given below can be identical.