Momentum is "strength or force gained by motion or by a series of events" 
- The company has had a successful year and hopes to maintain its momentum by introducing new products.
- The movie loses momentum toward the end. 
Mason Currey writes about
- . . . the importance of momentum. When I get straight down to something really important early in the morning, before checking email, before interruptions from others, it beneficially alters the feel of the whole day: once interruptions do arise, they're never quite so problematic.
There's something about starting and continuing a project: the mental energy you get when you keep going. It sustains you. Every bit of work you do provides feedback that makes you want to do some more.
Getting an early start can help. Also, beginning at the same time every day.
- Routine, in an intelligent man, is a sign of ambition. -- Auden