Science Buddies: "Ask an Expert"

Hi there,
As I was looking through the "Grow Plants in Microgravity with an Arduino Clinostat" science project I was completely intrigued in doing it for my local science fair, but I had one question in mind. I was wondering how Ben Finio came up with the formula to calculate the gravity of lunar and other celestial bodies by only adjusting the incline of the petri dish. He mentioned the formula of sin^-1(x) in order to calculate the degrees of incline in which the petri dish should pose, but I didn't understand how that formula worked. I hope someone can tell me and educate me on how that formula derived and was used in this expierement.
Thanks,
ani_gudi

Hi - this might be difficult to understand if you haven't taken trigonometry yet. In this case, the angle is the angle between the petri dish's axis of rotation and the horizontal direction. You multiply the sine of this angle by Earth's gravity to get the effective gravity experienced by the plants:

clinostat gravity = earth gravity x sin(angle)

If the petri dish is perfectly vertical, then its axis of rotation is perfectly horizontal, so the angle is zero. Since sin(0) = 0, then the effective gravity is zero. If the petri dish was horizontal, then the angle between its axis of rotation and the horizontal would be 90 degrees, so the plants would experience full earth gravity since sin(90) = 1.

You can rearrange this equation to calculate the required angle to get a certain relative amount of gravity:

angle = sin^-1(clinostat gravity/earth gravity)

Hope that helps! We would love to hear how this project goes if you try it out.