Hi In my textbook they were doing a derivation of the acceleration of a projectile flying on Earth. Although they used the center of the Earth as the frame of reference, they ended up with the linear combination of 3 quantities for the acceleration of the projectile, one of which they said was coriolis acceleration. However, I thought that coriolis force only exists in non-inertial frames and the center of the Earth should be an inertial frame shouldn't it? Another question I have is that my physics text states that Earth is considered approximately an inertial frame because it's centripetal acceleration around the Sun is insignificant compared to Earth's gravity (almost direct quote). I don't really get this statement, can someone explain this? Thanks.