"In motion" describes something moving or actively happening, not still. It can be physical movement or a process that has started and is progressing.
An angel is an intelligent essence, always in motion. It has free will, is incorporeal, serves God, and has been bestowed with immortality. Only the Creator understands its true nature. John of Damascus
Sex is emotion in motion. Mae West
I realized what you could do in motion pictures by surrounding yourself with geniuses. Richard Donner
The force which a body at rest exercises on a body in motion impinging upon it. Latin Proverb
Fireflies shine only when in motion. American Proverb
The force which a body at rest exercises on a body in motion impinging upon it. [Stolid immobility or masterly inactivity.]. Latin Proverb