The discussion revolves around the implications of downward acceleration for an elevator that is moving upward. Participants explore the relationship between acceleration and velocity, particularly in the context of free body diagrams and coordinate system conventions.
Participants generally agree on the interpretation of downward acceleration as indicating a decrease in upward velocity. However, there is no consensus on the best convention for defining positive and negative directions in the coordinate system.
Some assumptions about the coordinate system and the definition of acceleration may not be explicitly stated, leading to potential variations in interpretation.
It means that it is going up, but slowing down. Like it is going up from the lobby and about to stop at some upper floorjwviviang said:TL;DR Summary: I just have a question (I don't know how to word this summary, sorry)
If an elevator is moving upward, what does a downward acceleration mean?
In principle you can have up be either positive or negative, whatever you prefer. However, I personally think that having up be negative is confusing, so I would recommend usually choosing up positive.jwviviang said:When applying the free body diagram, will the positive direction be upwards since the elevator is moving up?
If acceleration has a component opposite to velocity, then the object is slowing down.jwviviang said:If an elevator is moving upward, what does a downward acceleration mean?
You are free to choose the orientation of your coordinate system axes, as long you apply that convention consistently.jwviviang said:When applying the free body diagram, will the positive direction be upwards since the elevator is moving up?
A.T. said:If acceleration has a component opposite to velocity, then the object is slowing down.You are free to choose the orientation of your coordinate system axes, as long you apply that convention consistently.
I see now. So if a question says (for example) "...moving upward elevator...if the elevator has a downward acceleration a = 1.4 m/s^2..." the downward acceleration means a = -1.4 m/s^2?Dale said:It means that it is going up, but slowing down. Like it is going up from the lobby and about to stop at some upper floor
In principle you can have up be either positive or negative, whatever you prefer. However, I personally think that having up be negative is confusing, so I would recommend usually choosing up positive.
So your acceleration would be negative and your velocity would be positive.
Yes, in the usual setup with up being positive.jwviviang said:I see now. So if a question says (for example) "...moving upward elevator...if the elevator has a downward acceleration a = 1.4 m/s^2..." the downward acceleration means a = -1.4 m/s^2?