|MLA Citation:||Bloomfield, Louis A. "Question 1544: What does it mean to coast?"|
How Everything Works 11 Dec 2017. 11 Dec 2017 <http://howeverythingworks.org/print1.php?QNum=1544>.
To clarify the term "net force," note that when an object is experiencing several separate forces, it doesn't accelerate in response to each one individually. Instead, it accelerates in response to the sum of all the forces acting on it: the net force. Remember that forces have directions associated with them (forces are vector quantities), so when you sum them you must consider their directions carefully. The proper force to consider in Newton's second law is actually the net force on the object. If you know both the net force on the object and the object's mass, you can predict the object's acceleration. And if the net force is zero, then the object doesn't accelerate at all — it coasts.