I would say that velocity is constantly changing when sitting in a chair on a rotating earth . Velocity is a vector quantity , it has magnitude and direction . But we never sense this acceleration , which itself must be constantly changing . Doesn't make sense to me .
Yes, on a rotating planet there will be a force created by the rotation. However, this is minuscule. Only about .034 m/(s ^2) at the equator and in the direction directly opposite to gravity, and it's constant. Less than 1/3 of one percent the gravitational force at the equator, and less elsewhere. So how would you feel it? As for the force of acceleration due to our orbit around the sun, which actually does change as the earth rotates, that is less than 0.0059m/(s^2) at a maximum and changing slowly over 24 hours. Do you honestly think you could feel that?
UA on flat earth , the force acts down towards the plane - this is measured quite easily and its effects can be predicted using kinetics and ballistics. I might be wrong here because I've not really looked into it but that's a much better fit than the gravity ( through attraction of mass by unknown means ) theory .
So, we are all okay with the problem of the energy involved? If the entire universe was only the mass of the RE, then it would take about 8x10^19 kilowatt hours of energy
every second. That is about
4 billion times the total energy used on the earth
every year. So, acceleration due to insane amounts of energy from unknown means.