Basic relationships between speed, radius, period, acceleration and force
Here is a demonstration of the relationships between orbital speed, radius, period, centripetal acceleration, and gravitational centripetal force for an object of mass m2 in orbit around an object of mass m1.
A polar orbit is one that goes over the top of each of the north and south poles. They are often used for surveying: to understand why, it is worth looking at this video of a polar orbit in Kerbal Space Program or this one from EUMETSAT.
Not every circular polar orbit will cover the whole surface of a planet. If you have a globe, or a good imagination, it is worth trying to work out what happens with polar orbits whose period is some exact multiple of the planet’s day.