The term momentum is from the 1690s in the scientific use in mechanics, "product of the mass and velocity of a body; quantity of motion of a moving body," from Latin momentum "movement, moving power." Figurative use, "force gained by movement, an impulse, impelling force," dates from 1782.
Move forward consistently no matter how fast or slow. Do something tiny every day. Seek progress, not perfection. No matter what happens, keep swimming.
Momentum in time, velocity of motion, slow and fast and slow