Basic Mechanics: Force Diagram in Elevator & Weight Calculation

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In summary, the force diagram is the same for a person in the elevator at rest or moving upwards or downwards at a constant speed. If the elevator is accelerating, the person will experience a normal force greater than what he would normally. The scale will read a higher reading.
  • #1
Leaping antalope
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Hi everyone, I am reviewing physics...and here comes a question that has confused me for a long time.

The question is about the elevator (lift) and a weighting scale...what is the force diagram on a person standing in the elevator on a weighting scale...1. when the elevator is going upwards? and 2. when the elevator is going downwards? How should i calculate the acceleration and the weight appear on the weighting scale if relative values are given?

Can anyone show me the force diagram and tell me how to do the calculatoins...thanks
 
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  • #2
Leaping antalope said:
Hi everyone, I am reviewing physics...and here comes a question that has confused me for a long time.

The question is about the elevator (lift) and a weighting scale...what is the force diagram on a person standing in the elevator on a weighting scale...1. when the elevator is going upwards? and 2. when the elevator is going downwards? How should i calculate the acceleration and the weight appear on the weighting scale if relative values are given?

Can anyone show me the force diagram and tell me how to do the calculatoins...thanks

The diagrams are the same as long as the elevator is going at constant speed, and they are the same as for a person in the elevator at rest. Did you mean to ask about upward acceleration and downward acceleration? You can have either one when the elevator is going up and when it is going down.
 
  • #3
OlderDan said:
The diagrams are the same as long as the elevator is going at constant speed, and they are the same as for a person in the elevator at rest. Did you mean to ask about upward acceleration and downward acceleration? You can have either one when the elevator is going up and when it is going down.

I know that the force diagram is the same when the elevator is at rest and when its at constant velocity. What i don't understand is that when the elevator is accelerating...when it speeds up AND when it slows down. What is the change in the normal force? and how will the weighting scale change?
 
  • #4
Well, the elevator has to provide its own acceleration to the person inside it, right?
 
  • #5
arildno said:
Well, the elevator has to provide its own acceleration to the person inside it, right?
So...the accelereation from the Earth is 10N/kg, when the elevator provides its own acceleration...can i add the two accelerations together?
What will be the force diagram?
Still don't get it!
 
  • #6
If the elevator is accelerating upwards, then the person will experience a normal force greater than what he would normally. Therefore the scale will read a higher reading.

If the elevator is descending, the person wil lexperience a normal force less than he would if he were standing on a non-accelerating platform. The scale will measure him as lighter.
 
  • #7
g' = g + a

Where g' is the observed acceleration of gravity, g is 9.8 m/s^2 and a is the acceleration of the elevator (if we define up to be the positive direction).

So if you are going down in an elevator accelerating at 2.0 m/s^2, g' is 9.8 + (-2.0) = 7.8 m/s^2. And if you are going up at the same a, g' is 9.8 + 2 = 11.8 m/s^2.

And then when you step on a scale and measure your weight F = mg, it becomes F = mg'
 
  • #8
ek said:
g' = g + a

Where g' is the observed acceleration of gravity, g is 9.8 m/s^2 and a is the acceleration of the elevator (if we define up to be the positive direction).

So if you are going down in an elevator accelerating at 2.0 m/s^2, g' is 9.8 + (-2.0) = 7.8 m/s^2. And if you are going up at the same a, g' is 9.8 + 2 = 11.8 m/s^2.

And then when you step on a scale and measure your weight F = mg, it becomes F = mg'

I see. Thanks
 
  • #9
Leaping antalope said:
Hi everyone, I am reviewing physics...and here comes a question that has confused me for a long time.

The question is about the elevator (lift) and a weighting scale...what is the force diagram on a person standing in the elevator on a weighting scale...1. when the elevator is going upwards? and 2. when the elevator is going downwards? How should i calculate the acceleration and the weight appear on the weighting scale if relative values are given?

Can anyone show me the force diagram and tell me how to do the calculatoins...thanks

Here is more on basic Newtonian Mechanics...with lots of exercises

https://www.physicsforums.com/showthread.php?t=72040


marlon
 

Related to Basic Mechanics: Force Diagram in Elevator & Weight Calculation

1. What is a force diagram in the context of elevator mechanics?

A force diagram in elevator mechanics is a visual representation of all the forces acting on an elevator. This includes the weight of the elevator itself, the tension in the elevator cables, and any external forces such as air resistance or friction.

2. How is the weight of an elevator calculated?

The weight of an elevator can be calculated by multiplying its mass by the acceleration due to gravity (9.8 meters per second squared). This calculation takes into account the force of gravity acting on the elevator.

3. What is the significance of knowing the force diagram and weight of an elevator?

Understanding the force diagram and weight of an elevator is crucial for ensuring the safety and proper functioning of the elevator. It allows engineers to design and maintain elevators that can safely support their intended load capacity and operate efficiently.

4. How does the force diagram change when an elevator is in motion?

When an elevator is in motion, the force diagram will show additional forces such as the kinetic energy of the moving elevator and the force of air resistance. These forces will change in magnitude and direction as the elevator accelerates, decelerates, or moves at a constant speed.

5. What factors can affect the weight calculation of an elevator?

The weight calculation of an elevator can be affected by various factors such as the number of passengers inside the elevator, the weight of any objects being transported, and the weight of the elevator itself. External factors such as elevation, air density, and temperature can also impact the weight calculation.

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