Does weight change in an elevator?

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Discussion Overview

The discussion revolves around whether a person experiences a change in weight when in an accelerating elevator, particularly as it ascends. Participants explore the definitions of weight, the effects of acceleration, and the implications of different physical frameworks.

Discussion Character

  • Debate/contested
  • Conceptual clarification
  • Mathematical reasoning

Main Points Raised

  • Some participants question whether an object gains weight in an elevator, noting that while mass remains constant, the variable "g" may be affected by acceleration.
  • There is a distinction made between defining weight as gravitational force (mg) versus the reading on a scale, leading to differing conclusions about weight change in an accelerating elevator.
  • One participant asserts that 'g' does not change in an accelerating elevator, but the normal reaction force, or apparent weight, does change.
  • Another participant introduces the concept of apparent weight in relation to inertia, suggesting that it may feel like weight increases at the start of ascent.
  • A participant references general relativity, indicating that in a coordinate system attached to the elevator, weight would appear to increase.
  • There is a mathematical proposal that apparent weight can be expressed as W=mg+ma, reflecting the effects of acceleration.
  • Discussion includes a note on how exam questions might frame the scenario, emphasizing the importance of definitions and the context of weight measurement in an elevator.

Areas of Agreement / Disagreement

Participants do not reach a consensus on whether weight changes in an elevator, as differing definitions and frameworks lead to multiple competing views.

Contextual Notes

Participants highlight that the definition of weight is crucial to the discussion, and the implications of acceleration and reference frames are not fully resolved. The discussion also notes that exam questions may require nuanced understanding rather than straightforward answers.

pb23me
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Does an object gain weight?

When a person is in an elevator and the elevator begins to go up...Does the person actually gain weight? I know mass will not change obviously, but does the variable "g" vary due to acceleration?
 
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It depends on your definition of "weight." Most physics textbooks define "weight" as "gravitational force" (which equals mg near the surface of the earth). In this case your weight doesn't change in an accelerating elevator.

Some sources (including Hewitt's "Conceptual Physics") define "weight" as "what a bathroom scale (or other similar device) reads." In this case, your weight does change in an accelerating elevator.
 


'g' is the acceleration due to gravity, which doesn't change when a person is in an accelerating elevator. What changes is the normal reaction, sometimes referred to as the apparent weight.

Note: posted simultaneously with jt
 


apparent weight as in inertia ? Making your weight increase in the in the beginning of ascend .
 


Classically, no, as pointed out. But in the GR framework, if your coordinate system is attached to the elevator, yes, the weight increases.
 


Should it be W=mg+ma?
 


Champdx said:
Should it be W=mg+ma?

That would be the "apparent" weight mentioned by Gokul and jtbell.
 


In an exam question, they are unlikely to ask you, "When a person is in an elevator and the elevator begins to go up, does the person gain weight?" because this depends on your definition of weight.

They are more like to ask you, "If a person is standing on some weighing scales inside an elevator. The elevator starts from rest, goes upwards, stops, and comes back down, and stops again. Describe, at different stages, the readings on the scale (giving reasons for your answer)."
 

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