Inertia Newton's 1st Law of Motion, aka the Law of Inertia, states that an object at rest will tend to remain at rest, and a moving body keeps moving in a straight line at a constant speed. Well - as long as any forces acting on it are balanced. If they're not, then there is a "net force" which willl change the velocity of the object - changing its speed, direction, or both. Friction often seems to deny Inertia's truth. Friction always opposes motion between surfaces, causing them to stop - or even to START - moving, just as long as the motion is not between the surfaces with friction. Tools See a list of terms used in these activities. Matching Flashcards (Java / non-Java) Concentration Activities created by: Sandy Schuman This activity was created by a Quia Web subscriber. To learn how to make your own, just like this, click here.