Why does rocking a baby make the baby go to sleep?

Just a theory: While in the womb mom walks and moves all the time rocking the baby all the time. Baby is more active a night when mom is still. Baby's like the motion!

Bad idea that works: This re-created the motion of the womb.Years ago an engineer developed and sold a device that gently rocked the bed. It can teach the baby to need this to fall asleep, every time they wake at any time of night.I encourage parents to avoid setting this pattern.