Increasing the value of acceleration via elevator.

[chaser0]

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When you Accelerate upwards with an elevator, you increase the value of g.

Can someone help me understand this? Because g is downwards, and you are accelerating upwards, shouldnt the final acceleration be (g-a)? Which would be a smaller value...

 

[hellocubed]

hmmm I am not quite sure.
When you are standing on a scale in an elevator and you go upwards, you do become heavier. I think that much is naturally easy to conceptualize, but I am not exactly sure why.

Perhaps it has something to do with action, reaction?

 

[Barato]

When you Accelerate upwards with an elevator, you increase the value of g.

Can someone help me understand this? Because g is downwards, and you are accelerating upwards, shouldnt the final acceleration be (g-a)? Which would be a smaller value...

In order to visualize what is happening it is best to first draw a free body diagram of the entire system in question (the elevator and the observer, individual in the elevator).

When you have an acceleration in the positive y direction (upwards), you take the sum of the forces in the y direction:

(Sum) Forces_y-direction = (mass of individual)(acceleration in y direction)

After drawing the diagram it can be seen that:

Normal Force (Elevator on Person) - Weight (Person) = Mass_person*Acceleration_y

or

N - mg = ma_y

Since the weight of a scale measures the normal force of the individual on the elevator, solving for the Normal force N yields:

N = m(g+a)

Thus, a positive y (upward) acceleration yields a "greater weight" of the individual.

Hopefully that makes sense. I am not near a scanner or else I would have drawn it out on paper and uploaded it for you.

 

[hellocubed]

N = m(g+a)

Thus, a positive y (upward) acceleration yields a "greater weight" of the individual.

Wait could you explain the sign conventions?

N=m(g+a)

But if gravity is acceleration downwards, and the elevator is accelerating upwards, it would be:

N=m(-g+a)

Meaning, the more you accelerate up, the less you weight?




I understand you are correct, but a, wanting to wrap my brain around this. It should be intuitive but for some reason it's not for me...

 

[Morsetlis]

The elevator exerts an upward force on the scale, which exerts an upward force on you.

You exert a downward force on the elevator, and the scale on which you are standing.

Thus, you are accelerating upward with the same acceleration was the elevator, relative to the Earth.

If you were accelerating upward faster than the elevator, you would float in the air Inception-style.