Circular orbit
A circular orbit is the orbit at a fixed distance around any point by an object rotating around a fixed axis.
Below we consider a circular orbit in astrodynamics or celestial mechanics under standard assumptions. Here the centripetal force is the gravitational force, and the axis mentioned above is the line through the center of the central mass perpendicular to the plane of motion.
In this case not only the distance, but also the speed, angular speed, potential and kinetic energy are constant. There is no periapsis or apoapsis. This orbit has no radial version.
Circular acceleration
Transverse acceleration (perpendicular to velocity) causes change in direction. If it is constant in magnitude and changing in direction with the velocity, we get a circular motion. For this centripetal acceleration we have
where:
is orbital velocity of orbiting body,
is radius of the circle
is angular speed, measured in radians per unit time.
The formula is dimensionless, describing a ratio true for all units of measure applied uniformly across the formula. If the numerical value of is measured in meters per second per second, then the numerical values for will be in meters per second, in meters, and in radians per second.