B Elevator Question -- What does a downward acceleration mean?

AI Thread Summary
A downward acceleration in an upward-moving elevator indicates that the elevator is ascending but decelerating, preparing to stop at a higher floor. When applying a free body diagram, the positive direction can be defined as upwards, which is recommended for clarity. In this context, the upward velocity remains positive while the downward acceleration is negative. It is crucial to maintain consistency in the chosen coordinate system for accurate calculations. Thus, a downward acceleration of 1.4 m/s² would be represented as -1.4 m/s² when up is defined as positive.
jwviviang
Messages
2
Reaction score
0
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? When applying the free body diagram, will the positive direction be upwards since the elevator is moving up?
 
Physics news on Phys.org
jwviviang 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?
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

jwviviang said:
When applying the free body diagram, will the positive direction be upwards since the elevator is moving up?
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.
 
Last edited:
Reply
  • Like
Likes Chestermiller, vanhees71 and russ_watters
jwviviang said:
If an elevator is moving upward, what does a downward acceleration mean?
If acceleration has a component opposite to velocity, then the object is slowing down.

jwviviang said:
When applying the free body diagram, will the positive direction be upwards since the elevator is moving up?
You are free to choose the orientation of your coordinate system axes, as long you apply that convention consistently.
 
Reply
  • Like
Likes jwviviang and vanhees71
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.

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.
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?
 
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?
Yes, in the usual setup with up being positive.
 
Thread 'Gauss' law seems to imply instantaneous electric field propagation'

Thread 'Gauss' law seems to imply instantaneous electric field propagation'

Imagine a charged sphere at the origin connected through an open switch to a vertical grounded wire. We wish to find an expression for the horizontal component of the electric field at a distance ##\mathbf{r}## from the sphere as it discharges. By using the Lorenz gauge condition: $$\nabla \cdot \mathbf{A} + \frac{1}{c^2}\frac{\partial \phi}{\partial t}=0\tag{1}$$ we find the following retarded solutions to the Maxwell equations If we assume that...
View full post »

Thread 'Simple thought experiment with Stefan-Boltzmann law: energy'

Dear all, in an encounter of an infamous claim by Gerlich and Tscheuschner that the Greenhouse effect is inconsistent with the 2nd law of thermodynamics I came to a simple thought experiment which I wanted to share with you to check my understanding and brush up my knowledge. The thought experiment I tried to calculate through is as follows. I have a sphere (1) with radius ##r##, acting like a black body at a temperature of exactly ##T_1 = 500 K##. With Stefan-Boltzmann you can calculate...
View full post »
Thread 'A scenario of non-uniform circular motion'

Thread 'A scenario of non-uniform circular motion'

(All the needed diagrams are posted below) My friend came up with the following scenario. Imagine a fixed point and a perfectly rigid rod of a certain length extending radially outwards from this fixed point(it is attached to the fixed point). To the free end of the fixed rod, an object is present and it is capable of changing it's speed(by thruster say or any convenient method. And ignore any resistance). It starts with a certain speed but say it's speed continuously increases as it goes...
View full post »

Similar threads

I Calculating your weight in an elevator
Replies
24
Views
3K
B Forces inside a moving elevator
Replies
10
Views
2K
B How does an object gain potential energy?
2
Replies
54
Views
6K
B Maximum velocity for projectile motion?
Replies
25
Views
4K
B Understanding Newton's Third Law and the Net Force on Objects
Replies
10
Views
318
Mechanics: Elevator Accelerating Downward
Replies
10
Views
4K
B Fundamental Problems With Exam Question: Moving Truck & Acceleration
Replies
8
Views
2K
I Mass of Backpack in Moving Elevator
Replies
10
Views
2K
B What forces act on a bar when you do pull-ups?
Replies
5
Views
2K
Why Does a Balloon Fall Up in an Elevator?
Replies
5
Views
2K

Hot Threads

Recent Insights

Back
Top