# Escape velocity and formulas for circular orbits

In my class, we developed a list of formulas for circular orbits. One of them is E/m=1/2v2-GM/r=constant. To derive escape velocity we find for what v does E=0. But an orbit of this nature is certainly not circular! How can we apply the formula?

chroot
Staff Emeritus
Gold Member
Bound orbits are those with E < 0.

- Warren

Janus
Staff Emeritus
Gold Member
The formula given is true for all orbits; whether they be circular, eliptical, parabolic or hyperbolic.

As Warren pointed out, circular or eliptical orbits will have E<0

A parabolic orbit (the one followed by an object traveling exactly at escape velocity) E=0

For E > 0, you get a hyperbolic orbit.