Experimental Determination of “g” using an Elevator

[The Head]

Homework Statement

Experimentally determine the value of ‘g’ by measuring the displacement, velocity, time, and acceleration of an object (using LoggerPro) in an elevator.

Relevant Equations

g=(ma - Fn)/m

d=vi*t + 1/2at^2

I’m kind of stuck on this one. I don’t see how we can use the acceleration of an elevator to find anything about the value of g. We can of course get the acceleration of the elevator, but it feels like that would be independent of gravitational strength. I feel like we need the mass or the Normal Force, but those aren’t things we’re asked to measure. We are just measuring kinematical values in an elevator climbing or falling several stories. Help!

 

[berkeman]

Hmm. The only thing that comes to mind is measure the acceleration downward in the elevator that results in zero force on the scale measuring your weight in the elevator...

 

[The Head]

Hmm. The only thing that comes to mind is measure the acceleration downward in the elevator that results in zero force on the scale measuring your weight in the elevator...

Thanks for your reply— it seems like it is missing something to me too! Apparently the instructor says it can be done by continuously monitoring a, v, d, and t in the elevator. But to me, if you did this experiment on the Moon, all four of those variables could be the same as the values you get on Earth! So from that logic, it seems like whatever we measure has nothing to do with “g.”

 

[PeroK]

Thanks for your reply— it seems like it is missing something to me too! Apparently the instructor says it can be done by continuously monitoring a, v, d, and t in the elevator. But to me, if you did this experiment on the Moon, all four of those variables could be the same as the values you get on Earth! So from that logic, it seems like whatever we measure has nothing to do with “g.”

With the elevator at rest you could drop an object from known height $d$ that takes $t$ to hit the floor, and get $g = \frac{2d}{t^2}$.

 

[DEvens]

Um... What exactly does LoggerPro let you measure? What sensors have you got? If it measures the apparent weight of an object you would seem to not need the elevator, just a standard mass.