Will the Spring Balance Reading Return to Original mg at Constant Velocity?

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    Elevator Forces
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Homework Help Overview

The discussion revolves around the behavior of a spring balance reading when a person is in an elevator that accelerates upwards, moves at constant velocity, and then decelerates. The context involves understanding forces acting on the person as they transition through these states.

Discussion Character

  • Exploratory, Conceptual clarification, Assumption checking

Approaches and Questions Raised

  • Participants explore the relationship between acceleration, constant velocity, and the reading on the spring balance. Questions are raised about whether the reading returns to the original weight (mg) at constant velocity or remains elevated until deceleration.

Discussion Status

Some participants have offered insights into the forces at play, noting that at constant velocity, the net force is zero, which suggests a balance of forces. However, there is no explicit consensus on the implications of this balance for the scale reading.

Contextual Notes

Participants are considering the scenario without external cues, such as the elevator's movement indicators, which may affect their perception of the forces involved.

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Homework Statement



You are standing on a spring balance in an elevator. Draw a graph of scale balance reading VS time. At T0 you are at rest, accelerate upwards until T1 (where you reach constant speed) then decelerate from time T2 to T3.

Homework Equations



N/A

The Attempt at a Solution



So I know that the scale reading will go up when accelerating upwards because the net force must be upward, so the normal force is greater than mg. But, once it goes at a constant speed (T1) will the reading go back to original mg, or will it remain at the higher reading until it begins to decelerate again?

Thanks.
 
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genevievelily said:

Homework Statement



You are standing on a spring balance in an elevator. Draw a graph of scale balance reading VS time. At T0 you are at rest, accelerate upwards until T1 (where you reach constant speed) then decelerate from time T2 to T3.

Homework Equations



N/A

The Attempt at a Solution



So I know that the scale reading will go up when accelerating upwards because the net force must be upward, so the normal force is greater than mg. But, once it goes at a constant speed (T1) will the reading go back to original mg, or will it remain at the higher reading until it begins to decelerate again?

Thanks.
Draw the free body diagram for the "coasting" (constant speed) case. What's the net force on you?

Hint: Suppose the elevator has a particularly smooth and noiseless mechanism, and the floor counter and button lights were masked from you. Would you be able to distinguish between coasting at some constant speed and being at rest?
 
If the scale reading remained at the higher reading between T1 and T2, the normal force would be greater than mg. What can you conclude from that?
 
ohhh so since constant velocity, the net force is zero, so they must balance out again right?
 
genevievelily said:
ohhh so since constant velocity, the net force is zero, so they must balance out again right?
Right.
 

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