Hi Daw
This is probably another "information overload" discussions for most coaches, but I think you may appreciate it.
Most coaches think that it is momentum attained during the stride (forward weight shift) that causes the lead-leg to support the body's weight during the swing. This is actually not the case. There is no forward, or linear, body momentum when the batter rotates about a stationary axis. The reason weight on the back-foot becomes lighter and is no longer needed to keep the body from falling rearward as the body rotates is due to the gravity-defying properties of gyroscopic motion.
Here is a video that illustrates that principle.
Gyro "Precession" demo
Jack Mankin