Newton's Laws and Inertial Reference Frames
Why bodies keep moving, how force changes motion, and the frames in which the laws hold
Big Idea: A body left alone does not slow down by itself — it keeps its velocity. To change velocity you need a net force, and the change is described by F = ma. Forces always come in pairs. But all three of Newton's laws are only valid in a special class of reference frames called inertial frames; in an accelerating (non-inertial) frame they appear to break unless we invent extra "fictitious" forces.
By the end you will be able to:
- state and use Newton's three laws quantitatively,
- tell an inertial frame from a non-inertial one,
- explain inertia and why mass measures it,
- draw a free-body diagram and find the net force,
- solve numeric problems with F = ma in SI units.