G-force diagram on a roller coaster?

  • Thread starter eri139
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  • #1
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Homework Statement:
So for my physics class, we rode on a roller coaster with our phones to record g-force data in the x, y, and z directions. We recorded the moment we were going up, a moment at the top of the coaster when it was just flat (no change in height, but the coaster was still moving around in a semi-circle shape), and a moment as we were going down. We have to draw the g-force diagram for the roller coaster for all 3 moments. I get force diagrams for 2-d diagrams, with the force of gravity and the normal force and all that, but for 3-d I'm so lost. It also doesn't help that I don't know what the x, y, and z directions are, since I've seen xyz graphs online with the z pointing upwards and others with the y. I used the app Physics Toolbox, by the way.
Relevant Equations:
F = ma?
So, while we were going up the track, the z-direction gforce seemed to go up. It went from -1 to about -0.6. The x-direction seemed to be around 0, more or less? All x values were under 0.177. The y-direction decreased, more or less, from -0.4 to -0.9.

I think if I understand how the force diagram while going up I might be able to handle the rest of the moments we recorded.

I think the x direction is supposed to be the roller coaster going directly left or right, which would make the g-force 0, as shown in the data.

And I think the force of gravity should decrease with increasing altitude. So would that match up with the y-direction being the upwards direction, since it decreases? Or the z-direction, since it technically increases but the values are negative?

And, how would I draw the force diagram? Are there any forces that I would include besides gravitational and the force making the coaster go up? And which directions would all of my forces be acting? Should I draw in Fg with the two different components?

How do I do this??? Please help, I'm so confused!
 

Answers and Replies

  • #2
haruspex
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And I think the force of gravity should decrease with increasing altitude.
Just how high is this roller coaster? Were you equipped with space suits?!
Your meter measured forces exerted on it. Other than gravity, those forces would be associated with accelerations - not height, not velocity, just accelerations.
 
  • #3
BvU
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We recorded the moment we were going up
was there only one such moment ?

Describe your ride, clearly indicate how you held the phone all the time.
Best make a graph that represents the ride, with the recording periods indicated.
Do you still have the phone, so you can try to sort out which is up/down and which is forward ?
 
  • #4
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Just how high is this roller coaster? Were you equipped with space suits?!
Your meter measured forces exerted on it. Other than gravity, those forces would be associated with accelerations - not height, not velocity, just accelerations.
Ooh, okay. So the gravitational force wouldn't change with such a small difference in height?
But I can't think of any other accelerations that would be acting on the roller coaster besides the mechanisms that are making it move forward. Unless that acceleration was divided up into the z and y components, which is what the meter is measuring? And the x is just in a totally different direction and there's no forces acting that way?

Sorry, I'm just still a little bit confused by this.
 
  • #5
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was there only one such moment ?

Describe your ride, clearly indicate how you held the phone all the time.
Best make a graph that represents the ride, with the recording periods indicated.
Do you still have the phone, so you can try to sort out which is up/down and which is forward ?

The ride started with the roller coaster going up on a steady incline. Then, at a higher height, it just stayed parallel to the ground as it moved on a flat track in a semicircular shape. Then, it went down. We just held the phone close to our laps so they wouldn't fall off the ride.

So we just made a graph (my lab partner finally finished it so I only saw it now). The time spans about 5 seconds. The x is hovering around 0, as I said. But the y starts at -0.4 and then starts hovering around -0.75. The z starts at -1 and starts hovering around -0.8.

I've tried playing around with the phone but it's not really giving me any clear results.
 
  • #6
haruspex
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But I can't think of any other accelerations that would be acting on the roller coaster besides the mechanisms that are making it move forward. Unless that acceleration was divided up into the z and y components,
Certainly it is divided into those components by your recording device, but I am guessing those directions are not fixed in the ground frame. So the z component is normal to the incline of the track , right?
And it isn't just a question of moving forward.
The ride started with the roller coaster going up on a steady incline
If that's a straight line at a steady speed it should only record gravity, but because of the angle of the device it will be as z and y components.
If it is going faster then there will be some extra y component.
at a higher height, it just stayed parallel to the ground as it moved on a flat track in a semicircular shape.
So that’s a semicircle in a horizontal plane? If that is at constant speed, which way do you think the acceleration is?
 

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