This states that as a body moves around its orbit during a fixed amount of time, the line from the barycenter to the body sweeps a constant area of the orbital plane, regardless of which part of its orbit the body traces during that period of time. The transverse orbital speed is inversely proportional to the distance to the central body because of the law of conservation of angular momentum, or equivalently, Kepler's second law. Planets have bound orbits around the Sun. See radial elliptic trajectory, free-fall time. The motion will be on an ellipse with one focus at the other body.
![equation for average speed equation for average speed](http://www.wikihow.com/images/5/5a/Calculate-Instantaneous-Velocity-Step-11-Version-4.jpg)
In gravitationally bound systems, the orbital speed of an astronomical body or object (e.g.