Physlet Illustration: Riding Down in an Elevator

a = m/s2
A 50-kg box is riding in an elevator that accelerates downward at a constant rate. (Its velocity vector is shown in green.) The box rests on a digital scale that records its apparent weight in Newtons. Adjust the value of the acceleration (a < 9.8 m/s2) and see how it affects the apparent weight. How can the box become apparently "weightless"?

Hints

  1. Can you draw a free-body diagram for the box?
  2. What force is recorded on the scale?
  3. How does Newton's 3rd Law apply to this example?
  4. Apply Newton's 2nd Law to the box's motion, and determine the value of its acceleration that would make that force vanish.

Reference

See Walker, Section 5-6

Illustration written by Steve Mellema