Table of Contents

Inertial Frames


“What is an inertial frame?”

“Are we in one?”


Estimated Time: 10 min, including wrap-up

This SWBQ requires familiarity with Newton's Second Law. Students should first be asked to write down some properties of inertial frames. After having a few minutes to respond, but without further discussion, students should be asked whether the classroom is an inertial frame.

  • Confronts student understanding of inertial frames.
  • Sets the stage for the rest of the course.
  • (Newtonian) Inertial frames are precisely those in which Newton's laws are valid.

Wrap Up

  • What is a noninertial frame in special relativity?
  • Do the laws of physics apply in noninertial reference frames?
  • What is a “law” of physics?
  • Inertial frames are “not accelerating”.
  • The Earth is not an inertial frame.

Discuss student answers, emphasizing that the notion of inertial frame is context dependent: The classroom works fine for the Newtonian mechanics of small objects, with gravity viewed as an external force, but is noninertial due to rotational acceleration.

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