Science Buddies: "Ask an Expert"

Hi I am doing the Physics of Artificial Gravity Project and I am using the Arduino Science Journal accelerometer app on my phone. I am hoping you can explain which measurement I should use. The x, y, z are separate sensors on this accelerometer. Should I be using z (angular speed of angular velocity)? If I use that, it is measuring gravity plus any force from spinning the box, right?
If I use the linear accelerometer (it is the one that looks like a play button) it starts at 0 so I assume it is subtracting gravity and will just show the force of centripetal acceleration? There is a screenshot of recorded accelerometer data and it looks like the z was used?
Thanks!

Hi - if you haven't seen it, we have a detailed explanation of the differences between the XYZ and "linear" accelerometers on this page: https://www.sciencebuddies.org/science- ... elerometer

In this case, you are really only interested in the phone's acceleration in the horizontal plane (the plane that contains the circle where you're swinging the phone), which is where you're creating "artificial" gravity. You don't care about Earth's gravity pointing downward or any other small up and down wobbles of the phone.

So, assuming the phone is oriented such that the screen is facing in towards you or out away from you when you're twirling the phone around (not up at the sky or at the ground), then you would just use the Z accelerometer. This gives you the best measure of centripetal acceleration for this experiment. The linear accelerometer, although it cancels out Earth's gravity, will also detect any tangential acceleration or out-of-plane (up and down) acceleration, which isn't what you're interested in measuring.

Hope that helps!

It did help, thanks! Now I am wondering about the numbers I got. I spun my phone on a 2 m string at a speed of 1.76 s per revolution and I got a Centripetal Acceleration of 9.6? When I do the mathematical calculation 4 * pi^2r / T^2 I get 25.43 m/s^2
Thanks!

Hi - are you sure you were recording acceleration on the correct axis? 9.6 is very close to the acceleration of gravity (9.8m/s^2), which makes me think you were recording in the vertical direction instead of the horizontal direction pointing in toward the center of the circle. If you look at Figure 8 in the project, the recordings seem closer to what you got in your calculation.

Thanks for all the help! That's what I thought, but it gets really confusing (especially after all that spinning!)

No problem! Please don't hesitate to write back if you have more questions.