1. The problem statement, all variables and given/known data Imagine another planet with an acceleration of 10.00 m/s^2 at its equator when ignoring the rotation of the planet. The radius is 6.2 x10^6 m. An object dropped at the equator yields an acceleration of 9.70 m/s^2. Determine the length of 1 day on this planet. 2. Relevant equations 3. The attempt at a solution My teacher taught me how to solve this question, but there is just one step I don't understand 10.00m/s^2 - 9.70m/s^2 = 0.3m/s^2 (centripetal acceleration) why does subtracting these two values give us the centripetal acceleration?? On a test, if I get a similar question I know I have to subtract the two values, but I really want to learn the reason behind it.